chemistry igcse notes

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Planet Earth Natural cycles and resources The earth is distinctive in the solar system because it contains all three states of water on the surface. The water cycle takes place in the earth's surface. The energy for the water cycle comes from the sun Water evaporates from the sea and other areas of water and enters the atmosphere As it cools, it changes back into liquid water and forms clouds (tiny water droplet) As the water droplets stick together, rain clouds are formed and the water falls back to the surface as rain, snow or hail. Water then either flows back to the sea or is taken in by plants, which put it back into the atmosphere through their leaves. We use the water by trapping it on its way back to the sea. Carbon is the twelfth most common element in the earth, making up less than 1% of the crust. Without carbon, life would not exist. The source of carbon in the carbon cycle is carbon dioxide in the atmosphere. Only about 0.04% of the atmosphere is carbon dioxide. Green plants take carbon dioxide and water, combining them together to form glucose and oxygen. This process uses energy from the sun and is called photosynthesis. The word equation for photosynthesis is carbon dioxide + water → glucose + oxygen Carbon dioxide dissolves in water (mainly seawater), where it is used by animals ( to make their shells) and plants (in photosynthesis). The plants are eaten by animals, in which they gain the carbon from. Animal and plants die and rot away, or are buried, and slowly (over millions of years) are fossilised Tiny sea creatures die and their bodies fall to the bottom of the sea, where they slowly (over millions of years) change to limestone. Animals and plants breath out carbon dioxide when they respire food. The process of respiration uses oxygen from the air, and releases carbon dioxide. The word equation for respiration is oxygen + glucose →carbon dioxide + water When plants and animals decay after death, carbon dioxide is produced. Wood can be burnt. This combustion produces carbon dioxide. The word equation for combustion is carbon + oxygen → carbon dioxide Fossilised plants and animals form fossil fuels (coal, oil and gas). These produce carbon dioxide when they are burnt. Limestone produces carbon dioxide when it is heated in industry and when it moves back below the earth's crust. Carbon dioxide leaves the atmosphere by photosynthesis and by dissolving in water.

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Page 1: Chemistry IGCSE Notes

Planet Earth 

Natural cycles and resources The earth is distinctive in the solar system because it contains all three states of water on the surface. The water cycle takes place in the earth's surface. The energy for the water cycle comes from the sun Water evaporates from the sea and other areas of water and enters the atmosphere As it cools, it changes back into liquid water and forms clouds (tiny water droplet) As the water droplets stick together, rain clouds are formed and the water falls back to the surface as rain, snow

or hail. Water then either flows back to the sea or is taken in by plants, which put it back into the atmosphere through

their leaves. We use the water by trapping it on its way back to the sea.

Carbon is the twelfth most common element in the earth, making up less than 1% of the crust. Without carbon, life would not exist. The source of carbon in the carbon cycle is carbon dioxide in the atmosphere. Only about 0.04% of the atmosphere is carbon dioxide. Green plants take carbon dioxide and water, combining them together to form glucose and oxygen. This process

uses energy from the sun and is called photosynthesis. The word equation for photosynthesis is carbon dioxide + water → glucose + oxygen Carbon dioxide dissolves in water (mainly seawater), where it is used by animals ( to make their shells) and

plants (in photosynthesis). The plants are eaten by animals, in which they gain the carbon from. Animal and plants die and rot away, or are buried, and slowly (over millions of years) are fossilised Tiny sea creatures die and their bodies fall to the bottom of the sea, where they slowly (over millions of years)

change to limestone. Animals and plants breath out carbon dioxide when they respire food. The process of respiration uses oxygen from the air, and releases carbon dioxide. The word equation for respiration is oxygen + glucose →carbon dioxide + water When plants and animals decay after death, carbon dioxide is produced. Wood can be burnt. This combustion produces carbon dioxide. The word equation for combustion is carbon + oxygen → carbon dioxide Fossilised plants and animals form fossil fuels (coal, oil and gas). These produce carbon dioxide when they are

burnt. Limestone produces carbon dioxide when it is heated in industry and when it moves back below the earth's

crust. Carbon dioxide leaves the atmosphere by photosynthesis and by dissolving in water. Carbon dioxide is put back into the atmosphere by respiration and combustion. A problem we face is balancing the amount of carbon dioxide added and removed in the atmosphere.

Nitrogen is essential for plant growth and animal life. There is plenty of nitrogen in the atmosphere (78%) but is unreactive and it is difficult to get it into the soil for

plants use. Plants get their nitrogen from nitrates in the soil and animals get theirs from plants When animals and plants die and decay, their nitrogen returns to the soil as bacteria help their bodies to decay. There are bacteria that live in the roots of some plants (bean, clover etc) which can fix nitrogen from the

atmosphere so the plants can use it. The very high temperature of lightening can provide enough energy for nitrogen and oxygen in the atmosphere

to react. It then reacts with water in the atmosphere to form nitric acid. When it falls with rain, it forms nitrates in the soil.

Nitrogen is also taken from the air by chemical industry when fertilizers are made by the Haber process. The atmosphere

Page 2: Chemistry IGCSE Notes

Clean air has 79% nitrogen, 20% oxygen, 0.9% argon and 0.1% other gases (including carbon dioxide, water vapour, neon and other noble gases).

Nitrogen is used in the manufacture of ammonia and fertilizers in the Haber process. It is also used where an unreactive gas is needed to keep air away from certain products (eg: used to fill bags of chips to ensure that it does not get crushed or gets rancid )

Liquid nitrogen is used in cryogenics (storing of embryos and other types of living tissue at low temperature). Oxygen is used in the production of steel from cast iron. It is also used to make the high temperature flames

needed to cut and weld metals (oxy-acetylene torches). It is used in hospitals to aid the breathing of sick people. Argon is used to fill light bulbs to prevent the tungsten filament burning away. It does not react with tungsten

even at very high temperatures. Other noble gases are used in advertising signs, as they glow in different colours when electricity flows through

them.

Before any of the gases in the air can be used separately they have to be separated from the air in the atmosphere.

They can be separated using fractional distillation, which works because the gases have different boiling points. The fractional distillation involves two stages. First, the air must be cooled until it turns into liquid. Then the

liquid air is allowed to warm up again. The various gases boil off one at a time at different temperatures.

The main source of harmful gases is the burning of fossil fuels. Coal and oil are contaminated with sulfur, which produces sulfur dioxide when it burns. Sulfur + oxygen → sulfur dioxide Oxides of nitrogen are produced when air is heated in furnaces. Sulfur dioxide and oxides of nitrogen dissolve in rain water to produce acid rain. The effects of acid rain are limestone buildings are worn away, lakes are acidified and metals ions that are

leached out of the soil damage the gills of fish, which may die. Nutrients are leached out from the soil which the trees need and aluminum ions are freed from clays as aluminum sulfate which damage the tree roots. Trees are unable to draw up enough water through the damaged roots and it dies.

Wind can carry acid rain clouds away from the industrialised areas, causing the pollution to fall on other countries.

Lime can be added to lakes and the surrounding land, to decrease the acidity. Scrubbers can be fitted to power station furnaces. The acidic gases are passes through an alkaline substance

such as lime. This removes the acid, making the escaping gas less harmful. Sulfur is not a serious problem with motor vehicles. However, nitrogen dioxide is produced because of the high

temperature inside the engine's cylinder that causes nitrogen and oxygen in the air to react. Carbon monoxide is produced when it is not burned completely because of the lack of oxygen. Tetraethyl lead in petrol (leaded petrol) also causes pollution because it releases toxic metal lead into the environment.

The use of lead in petrol has decreased significantly.

Nitrogen dioxide causes acid rain and can combine with other gases in very hot weather to cause photochemical smog, which can cause breathing problems.

Carbon monoxide is a very toxic gas. It combines with the hemoglobin in blood and stops it from carrying oxygen. Very small amount of carbon monoxide can cause dizziness and headache. Larger quantities cause death.

Lead is a toxic metal and cause learning difficulties in children, even in small quantities. The body cannot easily get rid of lead, so small amounts can build up to dangerous levels over time.

Catalytic converters can be attached to the exhaust system of cars. They convert carbon monoxide and nitrogen dioxide into carbon dioxide and nitrogen.

If there is lead in the petrol being used, the catalyst becomes poisoned and will no longer work.

Methane, carbon dioxide, water vapour and oxides of nitrogen are causing global warming due to the greenhouse effect.

The atmosphere helps to remove the heat from the sun Global warming will cause the glaciers and polar ice to melt which will cause a rise in the sea level. The surface

temperature will increase and hurricanes and flooding will become more frequent. Carbon dioxide and methane are the two main problem gases.

Page 3: Chemistry IGCSE Notes

Carbon dioxide enter the air by respiration and burning and is removed by plants. Burning more fuel and cutting down forest increases the problem.

Methane is produced by animals. It is a by-product of digestion. It is also produced by the decay of food and other dead organic matter.

Sea and river There is plenty of water on the earth but most of it is in seas and oceans, where the salts are dissolved in it make

it unsuitable for most uses. The amount of fresh water (less than 3% of the total) is still sufficient but it is not always in the places needed.

Water from rivers and lakes, and from underground, can contain dissolved salts, solid particles and bacteria. The water purification process is used to remove the solid particles and bacteria. Water treatment involves filtering the water to removed solid particle and adding chlorine to kill bacteria which

could cause disease. Sea water can be made drinkable by desalination (taking the salt out). This can be done by distillation or by

forcing the water through special membrane using high pressure. Water is used in industries to cool down reactions, to transfer heat from one part of a factory to another or as a

solvent for other substances. 

The earth's crust The earth's crust is the top layer of solid rock of the planet. Metal ores are rocks which have a relatively high concentration of a mineral containing a certain metal. Rocks can be used for building and for the extraction of useful chemicals other then metals. The most useful of

these is limestone.

Limestone is used for making glass, building and roads, concrete, cement and mortar. It is also used in the manufacturing of steel and for neutralising acidic soils and lakes.

Limestone can be heated strongly to produce lime (quicklime, calcium oxide). A few drops of water is added to lime. The solid flakes and expands to form slaked lime. This reaction is strongly

exothermic. If more water is added to the slaked lime, an alkaline solution (limewater) is obtained. The cycle can be completed by bubbling carbon dioxide into limewater. A white precipitate of calcium carbonate

(limestone) is formed. This is called the limestone cycle.

Hydrogen gas has attractions as fuel. All that hydrogen produces on burning is water. When hydrogen burns, it produces more energy per gram than any other fuel. The problem of hydrogen being used as a fuel is that it is difficult to store and transport because of its low

density. Hydrogen is not cheap. The main method of obtaining it is by the electrolysis of water, which is not economical.

Fuel cell changes chemical energy into electrical energy. A hydrogen fuel cell can be used to power a car. Hydrogen has an efficiency of 60% compared with the 35% of petrol engine. The fuel cell supplies energy as long as the reactants are fed in to the electrodes. In the hydrogen-oxygen fuel cell, hydrogen and oxygen react together to form water. 2H₂ + O₂ → 2H₂O  

 

Page 4: Chemistry IGCSE Notes

Chemical reactions 

Chemical reaction and equation In physical change, the substance present remain chemically the same. No new substances are formed. Physical changes are often easy to reverse. Any mixtures produced are usually easy to separate.

The major feature of a chemical change, or reaction, is that new substances are made during the reaction. Many reactions are difficult to reverse. During a chemical reaction energy can be given out or taken in. When energy is given out, the reaction is exothermic When energy is taken in, the reaction is endothermic. There are more exothermic reactions than endothermic reaction 

Equations for chemical reactions. An equation includes only chemical substances involved. The law of conversation of mass states that the total mass of all the products of a chemical reaction is equal to

the total mass of all the reactants. 

Types of chemical reaction Synthesis (or direct combination) reactions occur where two or more substance react together to form just one

product. Heat is required to start synthesis reaction but, once started, it continues exothermically. Most synthesis reactions are exothermic Photosynthesis is a synthesis reaction that is endothermic. Photosynthesis takes place in green leaves of plants and requires energy from sunlight. Photosynthesis is a photochemical reaction. In photosynthesis, small molecules of carbon dioxide and water are used to make glucose. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ The green pigment chlorophyll is essential for this reaction because it traps energy from the sun.

Decomposition reaction have just one reactant, which breaks down to give two or more simpler products. Decomposition reactions are endothermic. They require heat energy. Decomposition caused by heat energy is called thermal decomposition.

A few salts can be made by synthesis reaction. But majority of the salts are made by either neutralisation or by

precipitation. Neutralisation reactions involve acids. When acids react with bases or alkalis, their acidity is destroyed. They are neutralised and a salt is produced. This is known as neutralisation reaction Precipitation reactions involve the formation of an insoluble product. Precipitation is the sudden formation of a solid either when two solutions are mixed or when a gas is bubbled

into a solution. Precipitation reactions are very useful in analysis and are also used in paint industry for making insoluble

pigments.

Displacement reactions are useful in working out the patterns of reactivity of elements of the same type. A displacement reaction occurs because a more reactive element will displace a less reactive one from a solution

of one of its compounds.

Combustion reactions are of great importance and can be very useful or destructive. Combustion of a substance involves its reaction with oxygen and the release of energy. These reactions are exothermic and often involve a flame. Combustion in which a flame is produced is described as burning Substances which undergo combustion readily and give out a large amount of energy are known as fuels.

Page 5: Chemistry IGCSE Notes

If a substance gains oxygen during a reaction, it is oxidised. If a substance loses oxygen during a reaction, it is reduced. Redox reaction is when oxidation and reduction takes place in the same reaction. A reducing agent is an element or compound that will remove oxygen from other substance. The commonest reducing agents are hydrogen, carbon and carbon monoxide. An oxidising agent is a substance that will add oxygen to another substance The commonest oxidising agents are oxygen (or air), hydrogen peroxide, potassium manganate (VII) and

potassium dichromate. Two common example of oxidation reaction in everyday lives are corrosion and rancidity. Corrosion is when the surface of a reactive metal is attacked by air, water or other substance around it. Rancidity is when food is oxidised and it is said to be rancid.

Oxidation is the loss of electrons Reduction is the gain of electrons. Oxidation is the increase in oxidation state of an atom or ion. Reduction is the decrease in oxidation state of an atom or ion.

Potassium iodide can be used as a test for any oxidising agent. When potassium iodide is added to a solution, the iodide ion is oxidised to iodine atom. The colour change is

from colourless to yellow-brown. Acidified potassium manganate(VII) can be used as a test for any reducing agent The colour change is from purple to colourless because when manganate(VII) ion is reduced, it loses its purple

colour Acidified potassium dichromate solution can also be used as a test for any reducing agent It changes from orange to green. 

Electrolysis Splitting up of ionic compound into negative and positive ions is called electrolysis Electrolytes can conduct electricity Electrolyte undergoes chemical change Carbon in the form of graphite is the only non-metallic element to conduct electricity. For a solid to conduct electricity, it must contain free electrons that are able to flow through it. There is no chemical change when an electric current is passed through a metal or graphite. An electrical conductor is a substance that conducts electricity but is not chemically changed in the process.

Many power cables are made of copper because it is a very good electrical conductor. Overhead power cables are made from aluminium because it conducts electricity well and has a low density. It is

also very resistant to corrosion. The cables then strengthened with a steel core. Leakage of power from overhead cables is prevented by using ceramic material.

Molten salts, solutions of salts in water, solution of acids and solutions of alkalis are electrolytes. The negative electrode is called the cathode and the positive electrode is called the anode. Positive ions move towards the cathode (negative electrode) and are called cations Negative ions move towards the anode (positive electrode) and are called anions The metal is always formed at the cathode The non-metal (except hydrogen) is always formed at the anode Oxidation takes place in the anode and reduction in the cathode. The apparatus in which electrolysis is carried out is known as electrolytic cell (or electro-chemical cell) A electrolytic cell has two electrodes (cathode and anode), electrolyte and an external current supply.

Electrolysis of a solution of salt has different products from those obtained by electrolysis of the molten salt. This

is because water itself produces ions. The molecule of water can split into hydrogen ions (H⁺) and hydroxide ions (OH⁻) Not enough ions are produced for pure water to conduct electricity very well. During electrolysis, the hydrogen and hydroxide are able to move to the electrode. They compete with the ions from the salt t be discharged at the electrode.

Page 6: Chemistry IGCSE Notes

The more reactive a metal, the more it tends to stay as ions and not be discharged. The hydrogen ion will accept electrons instead. Hydrogen molecule will be formed at the cathode.

The ions of less reactive a metal will accept electrons and form metal atoms at the cathode. If the ions of a halogen are present in a high concentration, they will give up electrons and molecules of the

halogens are formed at the anode. If no halogen ions are present, the hydroxide ions will give up electrons to form oxygen.

Electroplating can be used to coat one metal with another. The cathodes the object to be plated. The anode is made from the metal being used to plate the object. The electrolyte is a salt of the same metal. As the process proceeds the anode dissolves away into the solution and the object becomes thicker. The concentration of the solution remains the same. Electroplating can be used to give a protective coating to the metal underneath. During electroplating, the object must be free from impurities and it must be rotated.

  

Page 7: Chemistry IGCSE Notes

Acids , bases and salts 

Acids Vinegar, lemon juice, grapefruit juice and spoilt milk are all sour because of the presence of acids The above examples are organic acids and are present in animals and plant material Carbonic acid from CO₂ dissolved in water is present in fizzy drinks and is weak and dilute. Taste shouldn’t be a test to be tried since some acids can be dangerous to taste Some acids are corrosive. They eat their way through clothing, are dangerous to the skin, and some can attack

stonework and metals. They are called mineral acids An indicator is an easy way to detect if a solution is acidic or not. Indicators are substances that change color if put next to an acid or alkaline solution. The most common indicator is litmus paper. Most common acids are hydrochloric acid, sulfuric acid, nitric acid and ethanoic acid

Litmus Many indicators are extracted from plants. Indicators are colored substance that change color when added to an acid solution. The color change is reversed if the acid is cancelled out or neutralised. Colored extracts can be made from red cabbage or blueberries. The most used indicator is litmus, which is extracted from lichens. Litmus is purple in neutral and turns red when added to an acidic solution. The color change needs a chemical reaction. The molecules of the indicator are changed in the presence of an

acid. Substance with the opposite chemical effect to acids are needed to reverse the change and are called alkalis

which turn litmus solution blue Litmus paper can be also used which has been soaked in litmus solution and comes in blue and red form. Blue litmus paper turns red in acids and red litmus paper turns blue in alkalis. Litmus just gives a single color change. Phenolphthalein and methyl orange are other indicators that chemists find useful. They have different colour

changes from litmus. The changes are sometimes easier to see than that of litmus. 

Universal indicators Its another commonly used indicators Universal indicator is a mixture of indicator dyes. The idea of a universal indicator mixture is to imitate the colors of the rainbow when measuring acidity. It is useful because it gives a range of colors (a spectrum) depending on the strength of acid or alkali. Different acids produce different color. Same acid with different concentration will give different color. Strong acid turns universal indicator bright red. Weak acid turns it to orange-yellow. Strong alkali turns universal indicator to violet and weak turns it to blue.

pH scale pH scale is the most useful measure of the strength of an acid solution. It was worked out by the Danish biochemist Søren Sørensen who worked in the laboratories of the Carlsberg

breweries and was interested in checking the acidity of beer. The scale runs from 1-14 Acids have a pH less than 7. the more acidic a solution, the lower the pH Neutral substances have a pH of 7 Alkalis have a pH greater than 7

Acid and alkali solutions All acids contain hydrogen. Acids conduct electricity. They also conduct it better than distilled water. This conduction of electricity shows that the solution contains ions. Water contains very few ions In pure water, the concentration of hydrogen ions and hydroxide ions are equal.

Page 8: Chemistry IGCSE Notes

All acids dissolve in water to produce hydrogen ions meaning that all acid solutions contain more H⁺ ions than OH⁻ ions .

The pH scale is designed for the fact that acid solution has this excess of hydrogen ions The term pH is taken from the German 'potenz H(ydrogen)' which means the power of the hydrogen ion

concentration of a solution. Alkalis also conduct electricity better than distilled water. All alkalis dissolve in water to produce hydroxide ions and contain an excess of OH⁻ ions An indicator is affected by the presence of H⁺ or OH⁻ ions The characteristic properties of an acid and an alkali is shown when dissolved in water. Both acid and alkali can be used in concentrated or dilute solutions. When a large volume of water is added to a small amount of acid or alkali, it becomes dilute. When less amount of water is added it becomes concentrated 

Metal oxides and non-metal oxides Non-metals react/burn with oxygen to form gaseous non-metal oxides/ acidic oxides When water is added to these non-metal oxides, they dissolve and give a solution that turns blue litmus paper

red. Metals burn/react with oxygen to form solid metal oxides/ basic oxides. Some of these metal oxides dissolve in water to give a solution that turns red litmus paper to blue. Turning blue litmus paper to read shows that some of these solutions contain acids. The dissolved metal oxide reacts with acids to neutralise them. Water can be thought of as a hydrogen oxide with a pH of 7 and is therefore a neutral oxide Water is an exception to the rule that oxides of non-metals are acidic oxides. Neutral oxides does not react with either acidic oxides and basic oxides CO, NO and H₂O are neutral oxides. CO is a neutral oxide because it is poisonous An amphoteric metal oxide or hydroxide is one that reacts with both acidic oxides and basic oxides to form salt

and water (neutralisation) Zinc and aluminum are examples of amphoteric oxides Sodium hydroxide helps in the identification of amphoteric oxides When sodium hydroxide is added to zinc or aluminum, white precipitate of the metal is formed ZnCl(aq) + 2NaOH(aq) → Zn(OH)₂(s) + 2NaCl(aq)

Zn²⁺(aq) + 2OH⁻(aq) → Zn(OH)₂(s) This precipitate will re-dissolve if excess sodium hydroxide is added, because zinc is amphoteric. Zinc hydroxide + sodium hydroxide → sodium zincate + water

Zn(OH)₂(s) + 2NaOH(aq) → Na₂ZnO₂(aq) +2H₂O(l) Aluminum will give a similar reaction. Zinc and aluminum will re-dissolve because they are amphoteric They are reacting as acids with sodium hydroxide and produce a salt and water This test is used to distinguish between zinc and aluminum salts from others but not to distinguish them from

each other Ammonia solution (a weak alkali) is used to distinguish between zinc and aluminum from each other. The

precipitate of zinc will re-dissolve in excess of ammonia but aluminum's will not. Acid reactions in everyday life 

Alkalis and bases Alkalis are substances that dissolve in water to give a pH greater than 7 and turn litmus blue Alkalis contain excess of hydroxide ions (OH⁻ ) All metal oxides and hydroxides will neutralise acids, whether dissolved in water or not. Alkali is just a small part of a group of substances that neutralises acids, known as bases. All bases react in the same way with acids Alkali is just a small group from the extended family, which is the base. When bases react with acids, it forms salt. This type of reaction is known as a neutralisation reactions A base is a substance that reacts with acid to form a salt and water only Base + acid → salt + water

Page 9: Chemistry IGCSE Notes

Most bases are insoluble in water Bases which dissolve in water are known as alkalis An alkali is a base that is soluble in water. Alkalis are usually used in the laboratory as aqueous solutions Common alkalis are sodium hydroxide, potassium hydroxide, calcium hydroxide (limewater) and ammonia

(ammonium hydroxide). They contain OH⁻ ions, turn litmus blue and have a pH greater than 7. Sodium hydroxide and potassium hydroxide are the strongest compared to the others. Alkalis have a soapy feeling to the skin. They convert the oils in the skin to soap. Alkalis are used as degreasing agent because they convert oil and grease into soluble soap, which can be washed

away easily Bases neutralise acids to give a salt and water only. They are oxides and hydroxides of metals. They are mainly

insoluble in water. Alkalis are bases that dissolve in water. They feel soapy to the skin, turn litmus paper blue, give lotion with a pH

greater than 7 and give solutions than contain OH⁻ ions. Antacids are compounds that are used to neutralise acids indigestion and include magnesium oxide and

magnesium hydroxide, sodium carbonate and sodium hydrogencarbonate, and calcium carbonate and magnesium carbonate.

 Characteristic reactions of acids All acids can take part in neutralisation reactions. There are three major chemical reactions in which all acids will take part. An acid can react with a reactive metal, a base or alkali and a metal carbonate. In all three reactions, they produce a metal compound called a salt. In all three reactions, the hydrogen present in the acid is replaced by a metal to give the salt. A salt is a compound made from an acid when a metal takes the place of the hydrogen in the acid.

Metals that are quite reactive (not very reactive) can be used to displace the hydrogen from an acid safely.

Hydrogen gas is given off. Metal + acid → salt + hydrogen It is unsafe to try this reaction with very reactive metals because the reaction is too violent. No reaction occurs with less reactive metals.

When acids react with a base or an alkali, it is called neutralisation reaction Acid + base/alkali → salt + water

All carbonates give off carbon dioxide when they react with acids. Acid + metal carbonate → salt + water + carbon dioxide  

Acids and alkalis in chemical analysis All carbonate will react with acids to give off carbon dioxide. When carbon dioxide is passed into limewater (calcium hydroxide solution), it turns cloudy.

Some of the hydroxides are coloured. We can add an alkali to a salt and check the colour of the precipitate. Copper(II) salts give a light blue precipitate copper(II) hydroxide Iron(II) salts give a light green precipitate iron(II) hydroxide Iron(III) salts give a red-brown precipitate of iron(III) hydroxide

Some hydroxide precipitate are white Calcium, zinc and aluminium hydroxides are white. When excess of sodium hydroxide is added, zinc and aluminium hydroxide precipitate will re-dissolve to give a

colourless solution. Calcium hydroxide does not re-dissolve. When ammonia solution is added to zinc and aluminium salt, the form white precipitates. When excess ammonia solution is added to zinc and aluminium, only zinc hydroxide precipitate will re-dissolve.

Page 10: Chemistry IGCSE Notes

When ammonium salts react with alkali solutions, they produce ammonia gas. A damp red litmus paper turns blue when ammonia gas passes though it.

 Salts All common sodium, potassium and ammonium salts are soluble. All nitrates and ethanoate are soluble. Most chlorides and sulphates are soluble. Silver chloride and barium sulphate are insoluble. Almost all carbonates are soluble.

The crystals of some salts contain water of crystallisation. This water gives the crystals their shape and in some case it also gives them their colour. Such salts are known as hydrated salts When the hydrated salts are heated, their water of crystallisation is driven off as stream. The crystal lose their

shape an become a powder. Copper crystals are blue but when heated they are dehydrated to form a white powder. Crystals that have lost their water of crystallisation are said to be anhydrous. If water is added to anhydrous salts, the powder becomes crystals again and heat is given out. This can be used as a test for the presence of water. Preparing soluble salts Method A uses a solid metal, a solid base or a solid carbonate and an acid. An excess of the solid is added to the acid and allowed to react. Using excess of the solid makes sure that all the acid is used up. If the acid is not used up at this stage, the acid

would become concentrated when the water is evaporated later. When no more hydrogen is produced when a solid metal is used, the reaction with the acid has ended When the solution no longer turns blue litmus paper red when a solid base is used, the reaction with the acid has

ended When no more carbon dioxide is given off when a solid carbonate is used, the reaction with the acid has ended The excess solid is filtered out The filtrate (liquid part) is gently evaporated to concentrate the salt solution. This can be done on a heated

water bath. When crystals can be seen forming (crystallisation point), heating is stopped and solution is left to crystallise. The concentrated solution is cooled to let crystals form. The crystals are filtered off and washed with little distilled water. The crystals are then dried carefully between

filter papers.

Method B (titration method) involves the neutralisation of an acid with an alkali or a soluble carbonate. The acid solution is added to a burette. A burette is used to accurately measure the volume of solution added. A known volume of alkali solution is placed in a conical flask using a pipette. The pipette delivers a fixed volume accurately. A few drops of indicator (phenolphthalein or methyl orange) are added to the flask The indicator is added because both the acid and alkali are colourless. It is used to find the neutralisation point

or end-point. The acid solution is run into the flask from the burette until the indicator just changes colour. The volume of acid used is noted. The experiment can be repeated using the known volume of acid without adding the indicator or activated

charcoal can be added to remove the indicator and then the charcoal can be filtered off. The salt solution is evaporated and cooled to form crystals as in method A. Titration method is good to find the concentration of a particular acid or alkali solution. Preparing insoluble salts Some salts are insoluble in water. For example, silver chloride and barium sulphate. Precipitation is the sudden formation of a solid either when two gases are mixed or when a gas is bubbled into a

solution. For precipitation method, two aqueous solutions are used to form an insoluble salt.

Page 11: Chemistry IGCSE Notes

The aqueous solutions are added to each other and an insoluble salt is formed immediately. The insoluble salt falls to the bottom of the tube or beaker as a precipitate. The precipitate can be filtered off, washed with distilled water and then dried in a warm oven. Strong and weak acids and alkalis The higher the hydrogen ions (H⁺), the higher the acidity and the lower the pH Each pH unit means a ten-fold difference in the hydrogen ion concentration. Strong acids are completely ionised in solution in water Weak acids are partially dissociated into ions in solution in water

The higher the hydroxide ions (OH⁻), the higher the alkality and the higher the pH Strong alkalis are completely ionised in solution in water Weak alkalis are partially dissociated into ions in solution in water Strong acids and alkalis conduct electricity well.

An acid can be neutralised by an alkali to produce a salt and water only. Acid + alkali → salt + water The hydrogen ions from the acid and the hydroxide ions from the alkali combine to form water molecule. H⁺ + OH⁻ → H₂O

Hydrogen ion (H⁺) can be though of as a proton. An acid is a molecule or ion that is able to donate a proton (H⁺) to a base A base is a molecule or ion that is able to accept a proton  

Page 12: Chemistry IGCSE Notes

 

How far? How fast?Energy changes in chemical reactions Hydrocarbon molecules contain only the elements carbon and hydrogen. Methane is the simplest hydrocarbon molecule. When it burns, it reacts with oxygen. The products are carbon

dioxide and water vapour. Methane + oxygen → carbon dioxide + water CH₄ + 2O₂→ CO₂ + H₂O During this reaction, bonds are first broken and then new bonds are made. Chemical bonds are forces of attraction between atoms or ions. To break these bonds requires energy Breaking chemical bonds takes in energy from the surroundings. This is endothermic process. Making chemical bonds gives out energy to the surroundings. This is an exothermic process. When methane reacts with oxygen, the total energy given out is greater than the total energy taken in. overall,

this reaction gives out energy. It is an exothermic reaction. The overall change in energy for a reaction can be shown in an energy level diagram. Some bonds are stronger than others. They require more energy to break them, but they give out more energy

when formed. The combustion reactions of fossil fuels such as oil and gas are exothermic. Fossil fuels are useful because they easily ignite and burn and they are capable of releasing large amount of

energy as heat. Rusting reaction of iron generates heat for several hours and is used in pocket hand-warmers for cold regions.

Similar hand-warmers can be made using the heat given out by crystallisation of a solid from super-saturated solution

Endothermic reactions are far less common than exothermic ones. The reaction between nitrogen and oxygen is endothermic. It is one of the reactions that takes place when fuel is

burnt in car engines. Nitrogen + oxygen → nitrogen monoxide N₂ + O₂ → 2NO The bonding in the products is weaker than the reactant. Overall, energy is taken in by the reaction. Photosynthesis in green plants and the thermal decomposition of limestone are other important examples of

endothermic reaction.

The energy change in going from reactants to products in a chemical reaction is known as the heat of reaction. It is given the symbol ΔH. Δ means change in. the energy given out or taken in is measured in kilojoules (kJ). It is usually calculated per mole of a specific reactant or product.

If the reactant gives out heat to the surrounding, it has lost energy. It is an exothermic reaction. An exothermic reaction has a negative value of ΔH

If the reactant takes in heat to the surrounding, it has gained energy. It is an endothermic reaction. An endothermic reaction has a positive value of ΔH

Bond energy is the average value of the strength of a bond. The reactants involves breaking bonds so it is endothermic The products involves making bonds so it is exothermic The heat of reaction, ΔH, is the energy change on going from reactant to product. Heat of reactant = energy needed to break bonds - energy needed to make bonds

Although the vast majority of reactions are exothermic, only a few are totally spontaneous and begin without

help at normal temperatures. For example, sodium or potassium reacting with water. Energy is usually required to start a reaction. This is called activation energy (Eₐ). It is required because initially

some bonds must be broken before any reaction can take place. All reactions require some activation energy. For the reaction of sodium or potassium with water the activation

energy is low.

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Reactions can be thought of as the result of collisions between atoms, molecules or ions. In many collision, the colliding particles do not have enough energy to react and just bounce apart. A chemical reaction will only happen if the total energy of the colliding particles is greater than the required

activation energy of the reaction. Rates of reaction Rate of reaction = reactants consumed ÷ time taken or products used ÷ time taken Rate of reaction is the ratio of reactants consumed divided by time taken The rate of reaction depends on five things. The surface area of any solid reactant, the temperature of the

reactant, the concentration of the reactant, they use of a catalyst and the influence of light o some reactions.

The more finely powdered (or finely divided) the solid is, the greater is the rate of reaction. Reactions involving solids take place on the surface of the solid. A solid has a much larger surface area when it is powdered than when it is in larger pieces. An experiment to demonstrate this is the reaction between limestone or marble chips and dilute hydrochloric

acid. Calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ Two samples of marble chips are used. (A) has large pieces of marble chips and (B) has small pieces of marble

chips. Both the samples have the same mass. The experiment will be carried out twice. Once with A and the other with B. the volume and concentration of the

hydrochloric acid is same in both the experiments. A flask is kept on a balance. The marble chips and hydrochloric acid are added to the flask with a loose cotton

wool on top to prevent the liquid spraying out but allows carbon dioxide gas to escape. As the reaction starts, the flask will lose mass during the reaction. Balance reading are taken at regular time intervals and the loss of mass can be worked out. A mass against time graph can be plotted. Both experiments are plotted and compared. B will be more steeper

than A. this means that the gas is being produced faster in B. The total volume of gas released in the end of both experiments are the same. The rate of a reaction increases when the surface area of a solid reactant is increased

Reactions that produce gases are also very useful in studying of the effect of concentration on the reaction rate. The reaction between marble chips and acid could be adapted for this. Another reaction is the one between magnesium and excess dilute hydrochloric acid. Two experiments will be conducted. One with C and the other with D The acid is C is twice as concentrated as in experiment D Apart from the concentration of the acid, everything else is the same. The gas produced in the experiment is hydrogen and it is collected in a gas syringe. The volume of the gas produced is measure in regular time intervals. A graph can be plotted for both the experiments and it can be compared. The curve for C is steeper than for D The total volume of hydrogen at the end of both the experiments is the same. The rate of reaction increases when the concentration increases.

A reaction can be made to go faster or slower by changing the temperature of the reactants. The reaction between sodium thiosulphate and hydrochloric acid can be used. When sodium thiosulphate and hydrochloric acid reacts together, they form precipitate. The precipitate formed is used to measure the rate of reaction. A cross is marked on a piece of paper. A flask containing sodium thiosulphate is placed on top of the paper. Hydrochloric acid is quickly added. The yellow precipitate of sulphur produced is very fine and stays suspended in the liquid. With time, as more and more sulphur is formed, the liquid becomes cloudier and more difficult to see through. The time taken for the cross to disappear is measured. The faster the reaction, the shorter the length of time during which the cross is visible. The experiment is carried out several times with solutions pre-warmed to different temperatures.

Page 14: Chemistry IGCSE Notes

The solution and conditions of the experiments must remain the same, only the temperature will change. A graph can be plotted. The rate of a reaction increases when the temperature of the reaction mixture is increased.Catalysts A catalyst is a substance that increases the rate of a chemical reaction. The catalyst remains chemically

unchanged at the end of the reaction. Manganese(IV) oxide (MnO₂ ) is used as a catalyst for the decomposition of hydrogen peroxide. Hydrogen peroxide(H₂O₂) is a colourless liquid. When it decomposes, it forms water and oxygen. We can follow the rate of reaction by collecting the oxygen in a gas syringe. 0.5g of manganese(IV) oxide is added to hydrogen peroxide. The reaction is more faster with the presence of the catalyst. At the end of the reaction, the solid is filtered and dried and it's mass is check to be still 0.5g. If the amount of manganese(IV) oxide is doubled, the rate of reaction increases. If the manganese(IV) oxide is more finely divided (powdered), the rate of reaction will increase.

A small amount of catalyst can produce a large change in the rate of reaction. Since they are unchanged at the end of the reaction, they can be reused. Transition elements and their compounds make good catalysts.

Catalytic converter is used to reduce the polluting effect of a car exhaust fume. Car exhaust fumes contain gases such as carbon monoxide, nitrogen monoxide and unburnt hydrocarbons. The catalytic converter converts these gases to less harmful products such as carbon dioxide, nitrogen and

water. 2CO + O₂ → 2CO₂ 2NO + 2CO → N₂ + 2CO₂ 2NO → N₂ + O₂ Hydrocarbons + oxygen → carbon dioxide + water The converter contains a thin coating of rhodium and platinum catalysts. These catalysts have many tiny pores which provides a large surface area for reaction. The presence of lead in the petrol would poison the catalyst.

Living cells also produce catalysts called enzymes. Enzymes speed up reactions in organisms. Each enzyme works only for a particular reaction. Enzymes are protein. They are very specific They are temperature sensitive. The are denatured (inactivated) by heat. Most stop working above 45°C They are sensitive to pH. Most enzymes work best in neutral conditions around pH 7 Biological washing powders use enzymes to remove biological stains such as seat, blood and food. The enzymes in the washing powders are those which break down proteins and fats. Biological washing powders are used at a wash temperature of 40°C

Collision theory pg 213  

Page 15: Chemistry IGCSE Notes

Patterns and properties of metalsThe alkali metals Group I metals are called alkali metals They have a spectacular reaction with cold water. They don’t have many uses because they are so reactive and tarnish easily. They are stored under oil to stop them from reacting with oxygen and water vapour in the air. Sodium is used in sodium vapour lamps which are the yellow street light. The melting point of the alkali metals decreases as you go down the group They are all soft, low density metals. Lithium is the hardest but can still be cut with a knife. The metals get easier to cut going down the group. The density of the metals increases down the group. An exception is potassium which is slightly less dense than

sodium. Alkali metals are all reactive metals. They form positive ions with a single positive charge. They have similar formulae The react strongly and directly with non-metals to form salts. The salts are all white, crystalline, ionic solid that

dissolve in water

All alkalis metals react spontaneously with water to produce hydrogen gas and metal hydroxide. The reaction is exothermic. The heat produced can melt sodium and potassium as they skid over the surface of

the water. Lithium does not melt as it reacts. Lithium is the least reactive and caesium in most reactive. The reaction with water is the same for all the group I metals Metal + water → metal hydroxide + hydrogen

Aluminium Aluminium is the most common metal in the earth's crust. Aluminium is a light, strong metal and has good electrical conductivity. Aluminium is alloyed with other metals such as copper and is used in aeroplanes. It is used in overhead power lines because it has a low density ad is a good conductor of electricity. Aluminium is useful because it is protected from corrosion by a stable layer of aluminium oxide that forms in its

surface. The protective layer stops aluminium from reacting. This makes aluminium foil containers ideal for food

packaging as they resist corrosion by natural acids. Aluminium is also used for external structures such as window frames as they resist weathering.

Aluminium is used to extract metals from their ores because of its high reactivity. Aluminium can be used to produce iron form iron(III) oxide. The aluminium and iron(III) oxide are powdered and well mixed to help them react. The reaction is powerful, exothermic and produces iron in molten state. Because of this, the reaction is used to

weld together damaged railway lines. This reaction is an example of a redox reaction and is known as the thermit reaction.

Analytic test for aluminium pg 235

  

Page 16: Chemistry IGCSE Notes

Industrial inorganic chemistry The extraction of metals by carbon reduction The durability, tensile strength and low cost of steel makes it the mast widely used of all metals. Steel is used in ship-building and watch-making. Steel is mainly iron with between 0.2 and 1.5% carbon. The carbon makes the iron stronger and harder.

The main ore of iron if hematite (Fe₂O₃). Iron is obtained by reduction with carbon in a blast furnace The blast furnace is a steel tower about 30 metres high. It is lined with refractory (heat-resistant) bricks of

magnesium oxide which is cooled by water. The iron ore, coke (a form of carbon made from coal) and limestone (calcium carbonate) are added in the top of

the furnace. Blasts of hot air are sent in through holes near the bottom of the furnace. The carbon (coke) burns in the air blast and makes the furnace very hot. Coke burns with oxygen to form carbon dioxide. The carbon dioxide then burns with more coke to form carbon

monoxide C + O₂ → CO₂ CO₂ + C → 2CO The most important reaction in the furnace is the reduction of the ore by carbon monoxide. Fe₂O₃ + 3CO → 2Fe + 3CO₂ The iron produced flows to bottom of the furnace where it can be tapped off because the temperature at the

bottom is higher than the melting point of iron. One major impurity in the iron ore is sand (silica, SiO₂) The limestone added to the furnace helps to remove the sand. The limestone decomposes to lime in the furnace CaCO₃ → CaO + CO₂ The lime then reacts with silica to form calcium silicate which is molten CaO + SiO₂ → CaSiO₃ Calcium silicate is called slag. The slag will form a layer on top of the molten iron. It does not mix with iron because it is less dense than the

iron. Slag is useful because it prevents iron from reacting with oxygen The slag is tapped off separately. When solidified, the slag is used by builders and road-makers. The hot waste gases escape from the top of the furnace. They are used in heat exchangers to heat the incoming

air. This helps to reduce the energy costs of the process.

The iron produced in the blast furnace is called pig iron or cast iron and it is not pure. The iron contains about 4% carbon, and other impurities. The carbon makes the iron brittle which limits the usefulness of iron. Iron is added to a bessmer converter to remove the impurities The iron contains carbon, sulphur, silicon and phosphorus Oxygen is added and reacts with the impurities to from carbon dioxide, sulphur dioxide, silicon dioxide and

phosphorous pentoxide. This is called the basic oxygen process Carbon dioxide and sulphur dioxide being gases escape through the mouth of the vessel. Lime (calcium oxide) is added to the furnace and reacts with silicon dioxide and phosphorous pentoxide to form

slag which floats on top of the molten iron. Chromium, manganese, tungsten or other transition metals can be added to make different types of steel. These

metals prevent corrosion and make steel harder.

Page 17: Chemistry IGCSE Notes

When a metal is attacked by air, water or other surrounding substance, it corrodes. In iron and steel, the process of corrosion is called rusting Rust is a red-brown powder consisting mainly of hydrated iron(III) oxide (Fe₂O₃.xH₂O). Water and oxygen are essential for iron to rust. Seawater increases the rate of corrosion. Acid rain also increases the rate of rust. Aluminium is more reactive than iron, but does nor corrode in the damaging way that iron does. In aluminium, a very thin layer of aluminium oxide forms, which sticks strongly to the surface the metal. This

layer seals the metal and protects it from further attack. When iron corrodes, the rust forms in flakes, not a single layer. The attack on the metal can continue over time

as rust flakes come off. If chromium is alloyed with iron, a stainless steel is produced. Electroplating a layer of chromium on steel is used to protect some objects from rusting

The main ore of zinc is zinc blende (ZnS). The sulphide ore is heated very strongly in a current of air. This converts the sulphide to metal oxide. 2ZnS + 3O₂ → 2ZnO + 2SO₂ The sulphur dioxide produced can be used to make sulphuric acid. The metal oxide is heated in a blast furnace with coke. Carbon reduces the oxide to the metal ZnO + C → Zn+ CO Zinc vapour passes out of the furnace and is cooled and condensed in a condensing tray at the top of the

furnace. Zinc is used in alloys such as brass and for galvanising iron.

Copper is less reactive than iron and zinc. Most copper is extracted from copper pyrites (CuFeS₂) The copper produced from this ore is suitable for piping, boilers and cooking utensils. Then it is to be used for electrical wiring, it must be refined (purified) by electrolysis.

The extraction of metals by electrolysis Reduction by carbon does not work for more reactive metals. Extracting metals by electricity involves three stages. Mining the ore, purifying the ore and electrolysis of the

molten ore. Extraction of metals by electrolysis is expensive. Energy costs to keep the ore molten and to separate the ions

can be very high.

Bauxite is an impure form of aluminium oxide. Up to 25% of bauxite consists of the impurities iron(III) oxide and sand. The iron (III) oxide gives bauxite its red-brown colour. The Hall-Héroult electrolysis is the method for extracting aluminium. It was invented by Hall (an American) and

Héroult (a Frenchman) The bauxite is treated with sodium hydroxide to obtain pure aluminium oxide (alumina). The purified aluminium oxide (Al₂O₃) dissolves in molten cryolite (sodium aluminium fluoride, Na₃AlF₆). Cryolite is used to lower the temperature of aluminium oxide. The melting point of aluminium oxide is 2030°C

and the cryolite lowers it to 900-1000°C. The cryolite helps to reduce the energy cost. During the electrolysis of aluminium oxide, aluminium ions are attached to the cathode where they form liquid

aluminium metal. Al³⁺ + 3e⁻ → Al The oxide ions are attracted to the anode where they are discharged to form oxygen gas. 2O⁻² + 4e⁻ → O₂ The oxygen reacts with the anode (graphite) because of the high temperature and forms carbon dioxide or

carbon monoxide. C + O₂ → CO₂ 2C + O₂ → 2CO The anodes burn away and have to be replaced regularly. Ammonia and fertilisers

Page 18: Chemistry IGCSE Notes

Ammonia gas is colourless, has a distinctive smell, less dense then air and is very soluble in water to give an alkaline solution.

Ammonia is a raw material for fertilisers and explosives. Nitrogen is an unreactive gas and changing it into compounds useful for plant growth (nitrogen fixation) is

important for agriculture. Most plant cannot directly use ( or fix) nitrogen from the air. In the Haber process, nitrogen and hydrogen are directly combined to form ammonia N₂ + 3H₂ → 2NH₃ Nitrogen is obtained from air, and hydrogen from natural gas by reaction with steam. The two gases are mixed in a 1:3 ratio and compressed to 200 atmospheres. They are then passed over a series of catalyst beds containing finely divided iron. The temperature of the converter is about 450°C The reaction is reversible and does not go too a completion. A mixture of nitrogen, hydrogen and ammonia leaves the converter. The proportion of ammonia in the mixture

is about 15%. Ammonia is separated from the other gases by cooling the mixture. Ammonia has a higher boiling point than nitrogen and hydrogen, so it condenses easily. The nitrogen and hydrogen are re-circulated over the catalyst. The ammonia produced is stored as liquid under pressure. Most of the ammonia is used to manufacture fertilisers. Some of the ammonia is converted into nitric acid by oxidation.

Plants need nitrogen, which is important for health leaves. Plant need phosphorous, which is important for healthy roots. Plants need potassium, which is important for the production of flowers and fruit. Different plants need different composition of these elements. Sulphur and sulphuric acid Sulphuric acid is made from sulphur by the Contact process. Sulphur is produced by removing it from fuels such as gasoline. Sulphur can also be obtained from craters of volcanoes and is mined by pumping steam into sulphur beds

underground. The sulphur is then forced to the surface by compressed air. This is called Frasch process. Sulphur is then burned in air to form sulphur dioxide. Sulphur dioxide can also be produced by reacting a metal sulphite with an acid or by heating sulphide ores in

excess air The main reaction in the Contact process is the one in which sulphur dioxide and oxygen combine to form

sulphur trioxide. This reaction is reversible. The conditions for the production of sulphur trioxide is a temperature of 450°C and 1-2 atmospheres pressure.

Vanadium(V) oxide is used as the catalyst for the reaction. A yield of 98% sulphur trioxide is achieved. The sulphur trioxide produced is dissolved in sulphuric acid, and not water, in order to prevent environmental

problems of an acid mist which formed. The reaction with water is also highly exothermic. When sulphur trioxide and sulphuric acid react, they form oleum (H₂S₂O₇) When oleum reacts with water, it forms sulphuric acid S + O₂ → SO₂ 2SO₂ + O₂ ↔ 2SO₃ SO₃ + H₂SO₄ → H₂S₂O₇ H₂S₂O₇ + H₂O → 2H₂SO₄

Sulphur is used to vulcanise rubber, used in the manufacturing of fungicides and to produce sulphuric acid. Sulphur dioxide is used in the manufacturing of paper. It bleaches the yellow colour of the wood pulp and makes

it white. Sulphur is used instead of chlorine as it is less harmful to the environment. Sulphur dioxide is also used as a preservative in food industries. It kills the bacteria in the food to prevent it from

going bad. It is used in dried apricot and wine. Sulphuric acid is used in paints and pigments, fibres and dyes, tanning leather, soap and detergents, fertilizers

and chemicals and plastics. Sulphuric acid is used as a drying agent. It can dry gases like sulphur dioxide and hydrochloric acid, but cannot

dry a reducing gas like hydrogen sulphide or ammonia.

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Limestone Powdered limestone is used to neutralise acid soils and lakes acidified by acid rain. It is used in the blast furnace for the extraction of iron to remove impurities in the iron ore. Cement is made by heating powdered limestone with clay in a rotary kiln. It is then powdered and mixed with

gypsum (calcium sulphate, CaSO₄.2H₂O) to increase the cements setting time. Concrete is a mixture of cement and aggregate (stone chippings and gravel). The mixture is mixed with water

and can be poured into wooden moulds. It is then allowed to harden. Sodium carbonate (Na₂CO₃) is an important industrial chemical, which is manufactured from limestone. It is used

in the manufacture of glass, soaps, detergents, paper, dyes and other chemicals.

Lime (quicklime) is calcium oxide and is produced by roasting limestone in a lime kiln. The limestone decomposes by heat CaCO₃ → CaO + CO₂ Lime is used in agriculture to neutralise acid soils and to improve drainage in soils that contain a large amount of

clay. Lime is used with sodium carbonate and sand in making glass. Large amounts of lime are converted into slake lime, which is calcium hydroxide (Ca(OH)₂) Slaked lime is used in making bleaching powder, in making glass and for water purification. Slaked lime is mixed with sand to give mortar. When mixed with water and then allowed to dry, mortar sets into

a strongly bonded material to hold bricks together.  

Page 20: Chemistry IGCSE Notes

Organic chemistry The unique properties of carbon Carbon is unique in the variety of molecules it can form. Organic chemistry is the chemistry of carbon-containing compounds. Carbon atoms can join to each other to form long chains. Atoms of other elements can then attach to the chain The carbon atoms in a chain can be linked by single, double or triple covalent bonds. Carbon atoms can also arrange themselves in rings. Only carbon atoms can achieve all these different bonding arrangement to the extent that we see. There are more compounds of carbon than of all the other elements put together. Alkanes One of the simplest types of organic compound is the hydrocarbons A hydrocarbon is a compound that contains carbon and hydrogen only. Some hydrocarbons are saturated. These molecules contain only single covalent bonds between carbon atoms. Saturated hydrocarbons are known as alkanes. Alkanes are saturated hydrocarbons. Molecules of these compound contain only single bonds between the

carbon atoms in the chain. The simplest alkane contains one carbon atom and is called methane. Each molecule increases by a CH₂ The general formula for alkane is CₓH₂ₓ₊₂ (where x is the number of carbon atom) As the length of the hydrocarbon chain increases, the strength of the weak force of attraction between the

atoms is increased. The melting and boiling point of the alkanes increases as the chains become longer. The first for members of the alkane are gases, from 5 until 16 are liquids and 17 and above are waxy solids. All alkanes burn very exothermically and they make good fuels. When alkanes are burned in a good supply of air, the products are carbon dioxide and water vapour. Alkane + oxygen → carbon dioxide + water Methane forms the major part of natural. Propane and butane burn with very hot flames and are sold as liquefied petroleum gas (LPG). They are kept as

liquids under pressure but they vapourise easily when that pressure is released. Cylinders of butane (calor gas) are used in portable gas fires in the home. Butane is also used in portable

camping stoves, blow-torches and gas-lighters

The family of alkanes has similar chemical properties. Together they are an example of a homologous series of compounds.

 Alkenes The ability of carbon atoms to form double bonds give rise to the alkenes The alkenes are another family of hydrocarbons or homologous series. Alkenes are unsaturated hydrocarbons. Molecules of these compounds contain a carbon double bond

somewhere in the chain. The general formula for alkenes is CₓH₂ₓ (where x is the number of carbon atoms) Alkenes are unsaturated because it is possible to break the double bond and add extra atoms to the molecule. The simplest alkene contains two carbon atoms and is called ethene. The boiling point of the alkenes increases as the chains become longer. Alkenes are similar to other hydrocarbons when burnt. They give carbon dioxide and water vapour when they

are burnt in a good supply of air. Alkene + oxygen → carbon dioxide + water The presence of the carbon double bond in alkene makes it more reactive than alkanes. Other atoms can be

added to alkene when the double bond breaks.

Page 21: Chemistry IGCSE Notes

The carbon double bond (C=C) is the known as the functional group of the alkenes.

If an alkene is shaken with a solution of bromine in water, the bromine loses its colour. Bromine has reacted with the alkene producing a colourless compound. The double bond on the alkene breaks open and forms new bonds to the bromine atom.

When a double bond breaks open and adds two new atoms is known as an addition reaction. In addition reaction, two substances are added together to form a single product.

An alkane would give no reaction with bromine water. The solution would stay orange-brown. When alkene is added to acidified dilute solution of potassium manganate(VII), it turns from purple to colourless.

An alkane would produce no change. Hydrocarbon structure and isomerism The alkane family names all end in -ane. The alkene family names all end in -ene. The alkyne family names all end in -yne. The alcohol family names all end in -ol. The carboxylic acid family names all end in -oic acid. The prefixes to the names of the organic compounds are standard and indicate the number of carbon atoms in

the chain. When a halogen atom is introduced into a chain the name of the compound contains a prefix indicating which

halogen is present.

Molecules with the same molecular formula can have different structures. The same number of atoms can be connected together n a different way. This is known as isomerism.

The properties of compounds in isomers are quite similar. The difference shoes itself mainly in their melting and boiling points.

All alkanes and alkenes with four or more carbon atoms posses isomers. Isomers are compounds that have the same molecular formula but different structural formula.

Alkynes are a third family of hydrocarbons In alkynes, the molecules contain a triple carbon bond. The simplest alkyne contains two carbon atoms and is called ethyne. Ethyne is a highly reactive gas and is used to be known as acetylene. It is used in oxy-acetylene welding torches. Chemical reactions of the alkanes Alkanes are unreactive compounds They are saturated, so they cannot take part in addition reactions. They are unaffected by acids or alkalis. They can only take part in substitution reaction, particularly with the halogens.

Alkanes burns in a good supply of oxygen or air to form carbon dioxide and water If the air supply is limited, then the poisonous gas carbon monoxide is formed. Carbon monoxide is the product of incomplete combustion. Alkane + oxygen → carbon monoxide +water Carbon monoxide is toxic because it interferes with the transport of oxygen around our bodies by our red blood

cells. Incomplete combustion can also produce fine particles of carbon itself. These have not even reacted to produce

carbon monoxide. The fine carbon particles (or soot) which can glow yellow in the heat of a flame. They give a candle flame or the

safety flame of a Bunsen burner their characteristic yellow colour

The substitution reaction of alkane with chloride is a photochemical reaction. Alkane + chlorine → chloroalkane + hydrogen chloride Alkane and chloride react in the presence of sunlight. Ultra violet light splits chlorine molecules into separate energised atoms. These atoms then react with the

alkane.

Page 22: Chemistry IGCSE Notes

A chlorine atom replaces a hydrogen atom in an alkane molecule. The reaction can continue further as more hydrogen atoms are substituted. Compounds such as dichloroalkane, trichloroalkane and tetrachloroalkane are formed.

Trichloromethane (CHCl₃), or chloroform, was an early anaesthetic. However, a dose which can kill a patient is not much higher than the amount needed to anaesthetise a patient.

In 1956, halothane was discovered. It is a more useful anaesthetic. Its formula is CF₃CHBrCl Substituted alkanes are also good organic solvents. 1,1,1-tricholoroethane is one solvent that is used a lot, in dry

cleaning, for example. Chemical reactions of alkenes Alkenes are much more reactive than alkanes

Bromination is used as the chemical test for an unsaturated hydrocarbon. Bromine water is decolorised when shaken with an alkene. This reaction will also work with the bromine dissolved in an organic solvent such as hexane.

Hydrogenation is the addition of hydrogen to an alkene. The condition for this reaction are nickel catalyst and 150-300°C temperature. The product for this reaction is an alkane Alkene + hydrogen → alkane This reaction is also used in the manufacture of margarine from vegetable oils The vegetable oils include corn oil and sunflower oil. They are edible oil and contain long-chain organic acids

(fatty acids). The hydrocarbon chains of these acids contain one or more carbon double bond; they are unsaturated molecules.

Oils such as sunflower oil are rich in ply-unsaturated molecules. This means that the melting point is relatively low and the oil remains liquid at normal temperatures. By hydrogenating some, but not all, of the carbon double bonds, the liquid vegetable oil can be made into a solid but spreadable fat (margarine).

Animal fats tend to be more saturated than vegetable oils and fats. The animal fats in cream can be made into butter.

Many doctors now believe that unsaturated fats are healthier than saturated fats. This is why margarines are left partially unsaturated. Not all carbon double bonds are hydrogenated.

Olive oil is distinctive in having a high content of oleic acid, which is a mono-unsaturated fatty acid. Margarine can be made from olive oil without hydrogenation.

Another important addition reaction is the one used in the manufacture of ethanol. This is known as hydration. Ethanol is an important industrial chemical and solvent. It is formed when a mixture of steam and ethene is

passed over a catalyst of phosphoric(V) acid at a temperature of 300°C and a pressure of 60 atmospheres. Alkene + steam → alcohol Ethene + steam → ethanol This reaction produces the ethanol of high purity needed in industrial organic chemistry Alcohols The alcohols are a homologous series of compounds that contain -OH as the functional group. A functional group is a group of atoms in a structure that determines the characteristic reactions of a compound. The simplest alcohol contains one carbon atom and is called methanol. The general formula of the alcohols is CₓH₂ₓ₊₁OH and they be referred to as the alkanols

The industrial method of making ethanol involves the addition reaction of hydration. Ethanol is an important solvent a raw material for making other organic chemicals. Many everyday items use

ethanol as a solvent. These include paints, glues, perfumes, aftershave, etc

Ethanol and carbon dioxide are the natural waste products of yeasts when they ferment sugar. Sugar is present in all fruits and grains, and in the sap and nectar of all plants. Yeasts are found everywhere. They are single-cell, living fungi. They ferment sugar to gain energy; by anaerobic

respiration.

Page 23: Chemistry IGCSE Notes

As ethanol is toxic to yeast, fermentation is self-limiting. Once the ethanol concentration has reached about 14%, or the sugar runs out, the multiplying yeast die and fermentation ends.

The best temperature for carrying out fermentation is 37°C. The reaction is catalysed by enzymes in yeast Glucose → ethanol + carbon dioxide C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ Alcoholic drinks such as beer and wine are made on a large scale in vast quantities in copper or steel

fermentation vats. Beer is made from barley, with hops and other ingredients added to produce distinctive flavours. Beer contains

about 4% of ethanol Wine is made by fermenting grape juice. Wine contains between 8 to 14% ethanol. Stronger, more alcoholic drinks like whisky, brandy and vodka are made by distillation Fermentation can be carried out in the laboratory using a fermentation vessel. The air-lock allows gas to escape

from the vessel but prevents airborne bacteria entering The reactions of ethanol Ethanol burns with a clear flame, giving out quite a lot of heat. Ethanol + oxygen → carbon dioxide + water On a small scale, ethanol can be used as methylated spirit (ethanol mixed with methanol or other compounds) in

spirit lamps and stoves. Ethanol is a useful fuel that some countries have developed it as a fuel for cars.

Vinegar is a weak solution of ethanoic acid (previously called acetic acid). It is produced commercially from wine

by biochemical oxidation using bacteria (Acetobacter). Wine can also be vinegary if it is left open to the air. The same oxidation can be achieved quickly by powerful oxidising agents such as warm acidified potassium

manganate(VII). The colour of changes from purple to colourless Ethanol + oxygen → ethanoic acid + water C₂H₅OH + 2[O] → CH₃COOH + H₂O

Ethanol can be dehydrated to produce ethene. This is a way of preparing ethene in the laboratory. Ethanol vapour is passed over a heated catalyst. The catalyst can be aluminium oxide or broken pieces of porous

pot. Ethene is not soluble in water.

Alcohols react with organic acids to form sweet-smelling oily liquids known as ester. This is known as

esterification. Carboxylic acid + alcohol → ester + water Sulphuric acid is added to a catalyst for this esterification reaction Organic acids and ester. Carboxylic acids are another homologous series of organic compounds. The functional group of carboxylic acids are -COOH. The general formula is CₓH₂ₓ₊₁ (where x is the number of carbon atoms). Methanoic acid is HCOOH. Ethanoic acid is CH₃COOH The first two acids in the series are liquid at room temperature, though ethanoic acid will solidify if the

temperature falls only slightly. The acids dissolve in water to produce solutions that are weakly acidic. Methanoic acid is present in nettle stings and ant stings. Ethanoic acid is well known as the acid in vinegar.

Carboxylic acids will react with alcohols, in the presence of a few drops of concentrated sulphuric acid, to

produce an ester. This is known as esterification. Esters have strong and pleasant smells. Many esters occur naturally. Esters are responsible for the flavours in fruits and for scented flowers. Esters are used as food flavourings and in perfumes.

Page 24: Chemistry IGCSE Notes

The prefix in first part of the name in esters belongs to the alcohol and the prefix in the second part belongs to the carboxylic acid. Eg methanoic acid reacts with ethanol to form ethyl methanoate.

Animal fats and vegetable oils are esters. They are liquids or solids, depending on the size and shape of the molecules present. They are esters of glycerol, an alcohol with three hydroxyl (-OH) groups.

Fats and oils are an essential part of our diet and, although they are quite complex molecules, they are not polymers.

Each -OH group forms an ester with a molecule of a carboxylic acid. These acids tend to have long chains (sometimes called fatty acids).

Stearic acid (C₁₇H₃₅COOH) is one acid that occurs in animals fats. A complex molecule can be formed from glycerol and three molecules of stearic acid. This is the type of molecule

present in fats and oils. Vegetable oils tend to have long-chain acids that are more unsaturated than those in animal fats.

Soap is made by heating animals fats or vegetable oils with sodium hydroxide solution. The reaction involves

hydrolysis of ester links in the fats or oils. The esters present are broken down to glycerol and sodium salts of acids. Fat + sodium hydroxide → soap + glycerol This process is known as saponification   

Page 25: Chemistry IGCSE Notes

Petrochemicals and polymers Petroleum Fossil fuels were formed in the earth's crust from materials that was once living. Coal comes from fossil plant material. Petroleum (or crude oil) and natural gases are formed from the bodies of marine micro-organism. The formation of fossil fuels took place over geological period of time (many millions of years) These fuels are non-renewable and finite recourses. The three major fossil fuels are coal, petroleum and natural gas.

Petroleum is a mixture of many different hydrocarbon molecules. Most of the petroleum that is extracted from the ground is used to make fuel, but around 10% is used as a

feedstock, or raw material, in the chemical industry. Before it can be used, the various hydrocarbon molecules are separated by refining . This is done by fractional

distillation at an oil refinery At a refinery, petroleum is separated into different fractions; groups of hydrocarbons that have different boiling

points. These boiling points are related to the number of carbon atoms in the hydrocarbon. Separation of the hydrocarbons takes place in a fractional distillation column, or fractionating tower. At the start of the refining process, petroleum is preheated to a temperature of 350-400°C and pumped in at the

base of the tower. As it boils, the vapour passes up the tower. It passes through a series of bubble caps, and cools as it rises further

up the column. The different fractions cool and condense at different temperatures, and therefore at different heights in the

column. It is then collected on trays. Fractions at the top are called light and fractions at the bottom are heavy. Each fraction contains a number of different hydrocarbons. The individual single hydrocarbons can be obtain by

further distillation.

Larger molecules from the heavier fractions can be broken into smaller, more valuable, molecules. This process is called catalytic cracking.

Cracking takes place in huge reactor. In the reactor, particles of catalyst (example silica, alumina and zeolites) are mixed with the hydrocarbon fraction at a temperature around 500°C. the cracked vapours containing smaller molecules are separated by distillation.

All cracking reactions give either an alkane with a shorter chain than the original, and a short-chain alkene or two or more alkenes and hydrogen.

 Addition polymerisation All living things contain polymers. Protein, carbohydrates, wood and natural rubber are all polymers. Plastic is a synthetic polymer. Polymers are large organic macromolecules. Polymers are made up of small repeating units known as monomers joined together by polymerisation. Some polymers are homopolymers which contain only one monomer. Other polymers are copolymers which are made of two or different types of monomer. Alkenes take part in addition reaction where the double bond is broken and other atoms attach to the carbons to

form a large molecule. This is known as addition polymerisation. Poly(ethene) is a chemically resistant material that is very tough and durable, and a very good electrical

insulator. Poly(chloroethene) or polyvinyl chloride (PVC) is stronger and harder that poly(ethene) and is good for making

pipes for plumbing Poly(tetrafluoroethene) or polytetrafluoroethylene or Teflon or PTFE is very stable at high temperatures and

forms a very slippery surface. Poly(propene) is easy to shape by melting and moulding. It is used to make sturdy plastic objects such as crates.

It can also be drawn into long fibres for making ropes. 

Page 26: Chemistry IGCSE Notes

Condensation polymerisation Nylon is a copolymer of two different monomers, a diamine and a dicarboxylic acid. Each monomer consists of a chain of carbon atoms but they can be just drawn as boxes. At both ends of the monomer are functional group. An amine group (-NH₂) reacts with a carboxylic acid group (-COOH) to make a link between the two molecules. Each time a link is made, a water molecule is lost NH₂ + COOH → NHCO + H₂O This type of polymer is known as condensation polymerisation. Because an amide link (or peptide link) is formed during polymerisation, nylon is known as polyamide. The linkage of nylon is similar to that of proteins

Polyester are condensation copolymers made from two monomers. One monomer is has an alcohol group (-OH) and the other has a carboxylic acid group (-COOH) When the monomers react, an ester link is formed, with water being lost each time OH + COOH → COO + H₂O One polyester has the trade name Terylene.

Plastics are light, cheap and corrosion resistant and they can be easily moulded and dyed bright colours. Most plastics are not biodegradable which causes a problem because there are no micro-organisms that can

break them down. Some modern plastics are suitable for reuse.

Proteins are what cells are made of. All tissues and organs of our bodies are made up of protein. Enzymes, which are responsible for controlling the body's reactions, are proteins. Proteins are built from amino acid monomers. There are 20 different amino acids used Amino acids contain two functional groups -NH₂ and -COOH Glycine and alanine are two of the simplest amino acids. When they react together, an amide linkage or peptide

linkage is formed to produce a dipeptide. When this is repeated many times using different amino acids, a polymer is formed. Shot polymers (up to 15 amino acids) are known as peptides Chains between 15-100 amino acids are known as polypeptides. Chains involving more than 100 amino acids are called proteins. Proteins can be hydrolysed(broken down) to amino acid by heating in concentrated hydrochloric acid. This is the

reverse of the condensation process. The mixture of amino acids can be separated by chromatography. Amino acids are colourless substance so a locating agent is used. The locating agent reacts with the amino acid to produce coloured spots

Sucrose (C₁₂H₂₂O₁₁) and glucose (C₆H₁₂O₆) examples of carbohydrates. Carbohydrates are important source of energy in our bodies, and all living organisms. A carbohydrate is a compound contain carbon, hydrogen and oxygen only. The ratio of hydrogen to oxygen is

always 2:1 (as in water) All long-chain carbohydrates (polysaccharides) are long-chain condensation polymers of sugar molecules

(monosaccharides). Starch, for example, is a polysaccharide found in plants. Starch and glycogen are two different polysaccharides of glucose, a monosaccharide. Polysaccharides can be broken down in the laboratory by warming with hydrochloric acid. (acid hydrolysis) The sugar present in hydrolysis mixture can be analysed by chromatography.. A locating agent must be used to

detect the spots, because the sugars are colourless. The presence of starch can be detected by testing with iodine solution. The solution turns a deep blue colour in

the presence of starch.

Fats and oils (lipids) are an essential part of our diet. They are an energy source. Lipids provide about twice as much energy per gram as do carbohydrates They provide thermal insulation for the body. Lipids are an essential part of cell membranes

Page 27: Chemistry IGCSE Notes

Tables Boiling points of the gases in the airGas Boiling point Proportion in mixture

Carbon dioxide -32 0.04

Xenon -108 -

Krypton -153 -

Oxygen -183 20

Argon -186 0.9

Nitrogen -196 79

Neon -246 -

Helium -249 -

 Advantages and disadvantage of hydrogen as a fuelAdvantages Disadvantages

Renewable if produced using solar energy

Lower flammability than gasoline

Virtually emission-free Zero emissions of CO₂ Non-toxic

Non-renewable if generated using nuclear energy or energy from fossil fuel.

Large fuel tank required There are no filling stations, where a car can be topped up with

hydrogen, at present. Engine redesign needed or a fuel cell system. Currently expensive

Properties of the three states of matterPhysical state Volume Density Shape Fluidity

Solid Has a fixed volume High Has a definite shape Does not flow

Liquid Has a fixed volume Moderate to high

No definite shape. Takes the shape of the container

Generally flows easily

Gas No fixed volume. Expands to fill the container

Low No definite shape. Takes the shape of the container

Flows easily

 Separation method for different type of mixtureMixture Method of separation

Solid + solid (powdered mixture) Uses some difference in properties. Examples: density, solubility, sublimation, magnetism

Suspension of solid in liquid Filtration or centrifugation

Liquid + liquid (immiscible) Using a separating funnel or decantation

Solution of solid in liquid To obtain solid: evaporation and crystallisationTo obtain liquid: simple distillation

Two or more liquids mixed together (miscible)

Fractional distillation

Page 28: Chemistry IGCSE Notes

Solution of two or more solids in a liquid Chromatography

 Difference between mixtures and compounds Mixture Compound

Joined or not The substances are not chemically joined. No reaction takes place.

The substances are chemically joined. A new substance is formed.

Composition It can be varied Definite composition

Properties The property of each substance stays the same

The property of the new substance is different

Separation Substance can be easily separated.It is separated using physical methods

Substance can not be easily separated.It is separated using chemical methods

 Difference between metals and non-metalsMetals Non-metal

Usually solid (except mercury) at room temperature

Usually solid or gas (except bromine) at room temperature

High melting and boiling point Low melting and boiling points

Good conductors of heat and electricity Poor conductors of heat and electricity (except graphite). They are insulators

Hard and dense Softer than metals (except diamond) and low density

Malleable and ductile Brittle

Grey colour except gold and copper Dull colours

Sonorous Not sonorous

 The properties of ionic and covalent compoundsProperties of a typical ionic compounds Reason for these properties

They are crystalline solids at room temperature

There is a regular arrangement of the ions in a lattice. Ions with opposite charge are next to each other

They have high melting and boiling points Ions are attracted to each other by a strong electrostatic force. Large amount of energy are needed to separate them

They are often soluble in water. They are not usually soluble in organic solvents

Water is attracted to charged ions and so many ionic solids dissolve

They conduct electricity when molten or dissolved in water

In liquids or solutions, the ions are free to move about. The can move towards the electrodes when a voltage is supplied

Properties of covalent compounds Reason for these properties

They are often liquids or gases at room temperature

These substances are made of simple molecules. The atoms are joined together by covalent bonds

They have low melting and boiling points The forces between the molecules (intermolecular force) are only very weak. Not much energy is needed to move the molecules further apart

They are often soluble in organic solvents. Very few are soluble in water

Covalent molecular substances dissolve in covalent solvents

Page 29: Chemistry IGCSE Notes

They do not conduct electricity There are no ions present to carry the current

AlloysAlloy Composition Properties

Brass Copper 70%Zinc 30%

Harder than pure copperGold coloured

Bronze Copper 90%Tin 10%

Harder than pure copper

Mild steel Iron 99.7%Carbon 0.3%

Stronger and harder than pure iron

Stainless steel Iron 70%Chromium 20%Nickel 10%

Harder than pure ironDoes not rust

Solder Tin 50%Lead 50%

Lower melting point than tin and lead

Difference between exothermic and endothermic reactionExothermic Endothermic

ΔH is negative ΔH is positive

Heat is given out Heat is taken in

It involves bond making It involves bond breaking

Energy of product is less than energy of reactant Energy of product is more than energy of reactant

Occurs spontaneously Cannot occurs spontaneously

Examples: rusting, neutralisation reactions, manufacture of ammonia

Examples: photosynthesis, decomposition reactions, reaction between nitrogen and oxygen

 Difference between metallic conductivity and electrolytic conductivityMetallic conductivity Electrolytic conductivity

Electrons flow Has a property of elements or alloys Takes place in solids and liquids No chemical change takes place

Ions flow Has a property of ionic

compounds Takes place in liquids and

solutions Chemical decomposition takes

place

 Common acidsType Name Formula Strong or weak Where found or used

Organic acid Ethanoic acid CH₃COOH Weak In vinegar

Organic acid Methanoic acid

HCOOH Weak In ant and nettle stringsUsed in kettle descaler

Organic acid Lactic acid CH₃CCH(OH) │ COOH

Weak In sour milk

Page 30: Chemistry IGCSE Notes

Organic acid Citric acid C₆H₈O₇ Weak In lemons, oranges and other citrus fruits

Mineral acids Carbonic acid H₂CO₃ Weak In fizzy soft drinks

Mineral acids Hydrochloric acid

HCl Strong Used in cleaning metal surfacesFound as the dilute acid in the stomach

Mineral acids Nitric acid HNO₃ Strong Used in making fertilisers and explosives

Mineral acids Sulphuric acid H₂SO₄ Strong In car batteriesUsed in making fertilizers, paint and detergents

Mineral acids Phosphoric acid

H₃PO₄ Strong In anti-rust paintUsed in making fertilizers

Indicator colour changesIndicator Colour in acid Neutral colour Colour in alkali

Litmus Red Purple Blue

Phenolphthalein Colourless Colourless Pink

Methyl orange Red Orange Yellow

 The reaction of elements with oxygenElement How it reacts Product Effect of adding water and testing with

litmus

Non-metals

Sulphur Burns with bright blue flame

Colourless gas (SO₂) Dissolves, turns litmus red

Phosphorus Burns with yellow flame White solid (P₂O₅) Dissolves, turns litmus red

Carbon Glows red Colourless gas (CO₂) Dissolves slightly, slowly turns litmus red

Metals

Sodium Burns with yellow flame White solid (Na₂O) Dissolves, turns litmus blue

Magnesium Burns with bright white flame

White solid (MgO) Dissolves, turns litmus blue

Calcium Burns with red flame White solid (CaO) Dissolves slightly, turns litmus blue

Iron Burns with yellow sparks Blue-black solid (FeO)

Insoluble

Copper Does not burn, turns black Black solid (CuO) Insoluble

 Common alkalis and basesType Name Formula Strong or

weakWhere found or used

Alkali Sodium hydroxide (caustic soda)

NaOH Strong In oven cleaners (degreasing agent)In making soap and paperOther industrial uses

Page 31: Chemistry IGCSE Notes

Alkali Calcium hydroxide (limewater)

Ca(OH)₂ Strong To neutralise soil acidityTo neutralise acid gases produced by power stations

Alkali Ammonia solution (ammonium hydroxide)

NH₃(aq) or NH₄OH

Weak In cleaning fluids in home (degreasing agent)Making fertilisers

Bases Calcium oxide CaO Strong Neutralising soil acidity and industrial wasteMaking cement and concrete

Bases Magnesium oxide MgO Strong In antacid indigestion tablets

 Solubility of different saltsSalts Soluble Insoluble

Sodium salts All are soluble None

Potassium salts All are soluble None

Ammonium salts All are soluble None

Nitrates All are soluble None

Ethanoate All are soluble None

Chlorides Most are soluble Silver chloride and lead(II) chloride

Sulphates Most are soluble Lead(II) sulphate, barium sulphate and calcium sulphate

Carbonates Potassium, sodium and ammonium carbonate

Most are insoluble

 Basicity of common acidsAcid type Name Formula Normal salts Acid salts

Monobasic (monoprotic) acid Hydrochloric acid HCl Chlorides

Monobasic (monoprotic) acid Nitric acid HNO₃ Nitrates

Monobasic (monoprotic) acid Ethanoic acid CH₃COOH Ethanoates

Dibasic (diprotic) acid Carbonic acid H₂CO₃ Carbonates hydrogencarbonates

Dibasic (diprotic) acid Sulphuric acid H₂SO₄ Sulphates hydrogensulphates

Tribasic (triprotic) acid Phosphoric acid H₃PO₄ Phosphates Dihydrogenphosphates and hydrogenphosphates

 Industrial catalystsIndustrial process Catalyst

Ammonia manufacture (Haber process) Iron

Sulphuric acid manufacture (Contact process) Vanadium(V) oxide

Margarine production (hydrogenation of fats) Nickel

Nitric acid manufacture (oxidation of ammonia) Platinum-rhodium

Page 32: Chemistry IGCSE Notes

Fermentation of sugar (alcoholic drinks industry) Enzymes (in yeast)

Conversion of methanol to hydrocarbon Zeolite ZSM-5

Decomposition of hydrogen peroxide Manganese(IV) oxide

 The effect of changing conditions in a chemical equilibriumCondition Effect of equilibrium position

Catalyst It does not affect the position of equilibrium but the reaction reaches equilibrium faster

Temperature Increasing the temperature makes the reaction move in the direction that takes in heat (endothermic direction).

Concentration Increasing the concentration of one substance in the mixture makes equilibrium move in the direction that produces less of that substance

Pressure This only affects reactions involving gases. Increasing the pressure shifts equilibrium to the direction that produces fewer gas molecules

 Flame colours of Group I and II metalsMetal ion Ion Flame colour

Lithium Li⁺ Red

Sodium Na⁺ Yellow

Potassium K⁺ Lilac

Magnesium Mg²⁺ No colour

Calcium Ca²⁺ Red

Strontium Sr²⁺ Scarlet

Barium Ba²⁺ Green

 Colours of transition element ions in solutionMetal ion in solution Formula Colour

Copper(II) Cu²⁺ Blue

Iron(II) Fe²⁺ Green

Iron(III) Fe³⁺ Red-brown

Chromium(III) Cr³⁺ Green

Cobalt(II) Co²⁺ Pink

Manganate(VII) MnO₄⁻ Purple

Chromate(VI) CrO₄²⁺ Yellow

Dichromate(VI) Cr₂O₇²⁺ Orange

 Reactivity seriesMetal

Potassium

Page 33: Chemistry IGCSE Notes

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Tin

Lead

Copper

Silver

Gold

Reaction of metals with air, water and dilute hydrochloric acidReactivity series

Reaction with air Reaction with water Reaction with dilute HCl

sodium Burns very strongly in air to form oxide

Reacts with cold water to give hydrogen

Reacts very strongly to give hydrogen

Calcium Burns very strongly in air to form oxide

Reacts with cold water to give hydrogen

Reacts very strongly to give hydrogen

Magnesium Burns very strongly in air to form oxide

Reacts with cold water to give hydrogen

Reacts very strongly to give hydrogen

Aluminium Burns less strongly in air to form oxide

Reacts with steam, when heated, to give hydrogen

Reacts less strongly to give hydrogen

Zinc Burns less strongly in air to form oxide

Reacts with steam, when heated, to give hydrogen

Reacts less strongly to give hydrogen

Iron Burns less strongly in air to form oxide

Reacts with steam, when heated, to give hydrogen

Reacts less strongly to give hydrogen

Lead Reacts slowly to form oxide layer when heated

Does not react Does not react

Copper Reacts slowly to form oxide layer when heated

Does not react Does not react

Silver Does not react Does not react Does not react

Gold Does not react Does not react Does not react

 Cast iron and carbon steelsMetal Carbon content (%) Properties Uses

Mild steel <0.25 Easily workedNot brittle

Car bodies, chains, pylons

Medium steel 0.25-0.45 Tougher than mild steel Car springs, axles, bridges

Page 34: Chemistry IGCSE Notes

High-carbon steel 0.45-1.5 Hard and brittle Chisels, cutting tools, razor blades

Cast iron 2.5-4.5 Cheaper than steelEasily moulded

Gear boxes, engine blocks, brake discs

 Alloys of steelSteel Composition Properties Uses

Stainless steel

Iron 74%Chromium 18%Nickel 8%

ToughDoes not corrode

Cutlery, surgical instruments, kitchen sinks, chemical plants

Tungsten steel

Iron 95%Tungsten 5%

Tough Hard, even at high temperatures

Edges of high-speed cutting tools

Manganese steel

Iron 87%Manganese 13%

ToughSpringy

Drill bits, springs

 AlkaneAlkane Molecular formula Number of carbon

atomsBoiling point Physical state at room

temperature

Methane CH₄ 1 -164 gas

Ethane C₂H₆ 2 -87 gas

Propane C₃H₈ 3 -42 gas

Butane C₄H₁₀ 4 0 gas

Pentane C₅H₁₂ 5 +36 liquid

Hexane C₆H₁₄ 6 +69 liquid

 Alkene Alkene Molecular formula Number of carbon atoms Boiling point Physical state at room temperature

Ethene C₂H₄ 2 -104 gas

Propene C₃H₆ 3 -47 gas

Butene C₄H₈ 4 -6 gas

Pentene C₅H₁₀ 5 +30 liquid

 AlcoholAlcohol Molecular formula Number of carbon

atomsBoiling point Physical state at room

temperature

Methanol CH₃OH 1 65 liquid

Ethanol C₂H₅OH 2 78 liquid

Propanol C₃H₇OH 3 97 liquid

Butanol C₄H₉OH 4 117 liquid

Pentanol C₅H₁₁OH 5 137 liquid

Page 35: Chemistry IGCSE Notes

 

Comparison of methods of ethanol productionEthanol by hydration of ethene Ethanol by fermentation

Originates from a non-renewable source (crude oil) Made from readily renewable resources

Small-scale equipment capable of withstanding pressure

Relatively simple, large vessel

A continuous process Need to start process again each time

A fast reaction rate A relatively slow process

Yields highly pure ethanol Ethanol must be purified by subsequent distillation

A sophisticated, complex method A simple, straightforward method

Carboxylic acidsAlkane Molecular formula Melting point

Methanoic acid HCOOH 9

Ethanoic acid CH₃COOH 17

 Petroleum fractionsFraction Number of carbon atom Boiling point Uses

Refinery gas 1-4 Below 25 Heating and cooking

Gasoline/petrol 4-12 40-100 Fuel in cars

Naphtha 7-14 90-150 To make chemical

Kerosene/paraffin 12-16 150-240 Fuel in jet engines Used as heating oil

Diesel oil/gas oil 14-18 220-300 Fuel in diesel engines

Fuel oil 19-25 250-320 Fuel in ships

Lubricating oil 20-40 300-350 Waxes and polishes

Bitumen residue Over 70 Above 350 Surfacing roads

 Uses of addition polymersPolymer Monomer Properties Examples of uses

Poly(ethene) (polyethylene, polythene, PE)

EtheneCH₂=CH₂

Tough, durable Plastic bags, bowls, bottles, packaging

Poly(propene) (polypropylene, PP)

PropeneCH₃CH=CH₂

Tough, durable Crates and boxes, plastic rope

Poly(chloroethene) (polyvinyl chloride, PVC)

ChloroetheneCH₂=CHCl

Strong, hard (not as flexible as polythene

Insulation, pipes and guttering

Poly(tetrafluoroethene) (polytetrafluoroethylene, Teflon, PTFE)

TetrafluoroetheneCF₂=CF₂

Non-stick surface, withstands high temperatures

Non-stick frying pans, non-stick taps and joints

Page 36: Chemistry IGCSE Notes

Poly(phenylethene) (polystyrene, PS)

Phenylethene (styrene)C₆H₅CH=CH₂

Light, poor conductor of heat

Insulation, packaging (foam)

  

Notes Magnesium reacts with oxygen to produce a brilliant white flame. Hydrochloric acid always gives a chloride salt Nitric acid always gives a nitrate salt Sulphuric acid always gives a sulphate salt Ethanoic acid always gives an ethanoate salt

 

Homologous series They have the same general formula They have similar chemical properties. They show a gradual increase in physical properties such as melting and boiling points. They contain the same functional group. The steeper the graph, the faster the reaction.A horizontal line means that the reaction has stopped.Empirical formula is the simplest possible whole-number ratio of the atoms in a compound.Molecular formula represents the actual number of atoms present in a molecule.Structural formula shows all the atoms in the molecule and how they are bonded together. Ways to prevent rust page 256