Reaction Rates Following the rate of a reaction.

Reaction rate is the speed of a reaction. The faster the reaction the higher the rate.

The progress of a chemical reaction can be followed by examining the reaction rate. There are several methods that can be used to follow a reaction rate.

Change in volume of any gases produced Change in mass of reaction mixture if gases are given off or taken in.

Other changes which can be monitored are: colour, pH, concentration and many more

As these changes happen over a period of time, the reaction rate is expressed as

Rate = Change in something Change in time.

Changes in Volume

The volume of the gas can be measured using the following experiments.

OR

1

0.1 g of Mg

water50cm3 of 1 mol/l

Measuring cylinder

gas

50cm3 of 1 mol/l

0.1 g of Mg

Gas syringe

As the experiment proceeds the volume of gas is measured and from these results a graph can be drawn.

Time (min) 0 2 4 6 8 10 12 14 16

Volume of gas (g) 0 40 70 90 100 105 105 105 105

The volume increases as more gas is formed.

Volume of gas

produced (cm3)

Time (min)

The graph is steeper at the beginning as the rate is higher (i.e. the gas is made more quickly)

The graph levels off at 10 minutes when no more gas is being made (i.e. the reaction is finished)

In this experiment the rate would be calculated by:

Rate = Change in volume of gas (cm 3 ) Change in time (min)

And would have the units: cm3/min

i.e. in the first 2 minutes between 2 and 6 min

Rate = 40 - 0 – 0 (cm 3) ) Rate =90 – 40 (cm 3 ) 2 – 0 (min) 6 – 2 (min)

= 40 (cm3)) / 2 (min) = 50 (cm3) / 4 (min)

=20 cm3/min = 12.5 cm3/min

2

Changes in mass

The mass change can be followed using the experiment below.

As the experiment proceeds the mass is measured.

Time (min) 0 2 4 6 8 10 12 14 16

Mass of flask (g) 127.3 126.5 125.9 125.5 125.3 125.2 125.2 125.2 125.2

The mass falls as the gas is made and escapes.

From these results a graph can be drawn of mass of flask against time.

Mass of flask

(g)

3

0.1 g of Mg

50cm3 of 1 mol/l

127.300gBalance

Time (min)

Rate = Change in mass of flask (g) Change in time (min)

And would have the units: g/min

The mass of gas formed can also be measured by taking the mass at any time away from the initial mass at time zero.

i.e. Before the reaction starts (time zero) the mass = 1277.3 At 2 minutes the mass =I 126.5g

Therefore the mass of gas formed = 127.3 g – 126.5g = 0.8g

We can therefore work out another row for our table: ‘Mass of gas formed’.

Time (min) 0 2 4 6 8 10 12 14 16

Mass of flask (g) 127.3 126.5 125.9 125.5 125.3 125.4 125.4 125.4 125.4

Mass of gas formed (g) 0.0 0.8 1.4 1.8 2.0 2.1 2.1 2.1 2.1

This will give a different shaped graph.

From these results a graph can be drawn of mass of flask against time.

Mass of gas formed

(g)

Time (min)

Rate = Change in mass of gas formed (g) Change in time (min) And

would have the units: g/min

The rate can be calculated from the graph or table Rate = Change in mass of gas formed (g)

Change in time (min) i.e. in the first 2 minutes between 2 and 6 min

4

Rate = 0.8 – 0.0 (g) Rate =1.8 – 0.8 (g) 2 – 0 (min) 6 – 2 (min)

= 0.8 (g) / 2 (min) = 1.0 (g) / 4 (min)

= 0.4 g/min = 0.25 g min

The rate is faster at the start of the reaction, which we can tell from the graph because it is steeper.

Atomic structure

Everything is made up of tiny particles called atoms. Atoms are mostly empty space made up of smaller sub-atomic particles.

Protons have a positive electrical charge.

Neutrons have no electrical charge and are neutral.

Moving around the nucleus are very small negatively charged electrons.

Nucleus containing the Protons and Neutrons(positive) (positive) (neutral)

Electron Cloud containing the Electrons (negative) (negative)

Name of particle Electric Charge Mass (amu) Position

Proton 1+ 1 NucleusNeutron 0 1 NucleusElectron 1- 1/1840 (almost zero) Electron Cloud

The number of protons in the nucleus of an atom is called the Atomic number. Every element has a different atomic number.

5

At the centre of the atom is the nucleus.This contains two types of particles, called protons and neutrons.

Spinning around the nucleus are very fast moving particles called electrons.They move in different levels, called shells.

The atom itself is neutral because the number of protons and electrons are the same. Therefore the positive charge of the nucleus is equal to the sum of the negative charges of the electrons.

Every atom has two numbers.

Atomic Number = number of protons

Mass Number = number of protons + neutrons

Electrons are not counted when calculating the mass number as they add so little to the atom’s mass.

Using a system called Nuclide notation, scientists can show the symbol, mass number and atomic number of an element.

Examples: Li F

Electrons move around the nucleus in orbits. The electron orbits are called shells.Each shell can hold only a certain number of electrons.

The first shell can hold a maximum of 2 electrons.The second and third shells can hold a maximum of 8 electrons. The last or outermost shell can hold a maximum of 8 electrons.

Electrons further away from the nucleus have more energy then those close to the nucleus.6

Atomic Number = Number of protons (also number of electrons)

E.g. an atom of the element carbon has an atomic number of 6. Its electrons are arranged so that each electron in the second shell is in a separate quarter of the shell.electron arrangement 2,4

An atom of the element oxygen has an atomic number of 8. Its electron arrangement is 2,6 O

Electron arrangement and properties

Sodium has an atomic number of 11. So its electron arrangement is 2,8,1 Na

If we look at Group 1 (the alkali metals)

These metals all react violently with water and form alkalis. They all have similar chemical properties.

All of the alkali metals one electron in their outer shell.

Lithium Li 2,1Sodium Na 2,8,1Potassium K 2,8,8,1Rubidium Rb 2,8,18,8,1Caesium Cs 2,8,18,18,8,1

If we look at Group 8 (0) (the Noble)

All the elements in group 0, the noble gases, are inactive and have virtually no chemistry. The outer shell is Full, (8 outer electrons, except He which is full with 2 outer electrons). Helium He 2,Neon Ne 2,8Argon Ar 2,8,8,Krypton Kr 2,8,18,8 Ne

7

Xenon Xe 2,8,18,18,8,Radon Rn 2,8,18,32,18,8,

It is the number of electrons in the outer shell, which gives atoms their properties.

Isotopes All atoms of an element must contain the same number of protons, but they can contain different numbers of

neutrons.

We can therefore get atoms of the same element with different masses.

These are called isotopes.

Isotopes: atoms with:

Same number of protons but different number of neutrons

OR

Same Atomic Number but different Mass Number

35 37

17 17

e.g.35Cl has 17 protons and 18 neutrons 37Cl has 17 protons and 20 neutrons

RELATIVE ATOMIC MASS (RAM) (page 4 of the data book)

Most elements contain a mixture of isotopes.

e.g. 37Cl 35Cl

exist in the proportions 25% 75%

The relative atomic mass is the average mass of all the isotopes an element has. It is rarely a whole number but has been rounded off to the nearest 0.5.

Relative Atomic Masses in the data book as always closest to the most abundant isotope.

The ram for chlorine (on page 4 of the data book) is 35.5.

This is because there is more 35Cl than 37Cl

It is possible to get equal proportions isotopes. e.g. 107Ag 109Ag

8

Cl Cl

50% 50%

The ram is therefore 108 (i.e. half way between 107 and 109).

Covalent Bonding

Non-metal elementsGroup 0 elements, the noble gases exist as single atoms, the monatomic gases. These elements are very unreactive.

The rest of the non-metallic elements exist as molecules which are groups of atoms joined together with covalent bonds.

Some elements exist as diatomic molecules (a molecule made of two atoms)There are seven non-metal elements in the periodic table which occur as diatomic molecules. They are : hydrogen (H2)

oxygen (O2)nitrogen (N2)fluorine (F2)chlorine (Cl2)bromine (Br2)iodine (I2)

Compounds

Covalent compoundsCovalent compounds contain only non-metal elements eg hydrogen oxide (pure water).Both hydrogen and oxygen are non-metals,so hydrogen oxide is covalent.

9

Covalent Bonding (non-metal/non-metal)

The Noble gases are stable elements as they have a full outer electron shell. Other elements react until their atoms obtain a full outer shell and become stable.

Non-metal atoms obtain a full outer shell by sharing their outer electrons with other non-metal atoms.

The sharing of outer electrons is called a COVALENT BOND.

The substance formed is then called a covalent molecule.

For example chlorine atoms have 7 outer electrons by two atoms sharing one electron each they both obtain a full outer shell.

Cl

Chlorine atom Chlorine atom Chlorine molecule (Cl 2)(7 outer electrons) (7 outer electrons) (each atom now has 8 outer electrons)

A full structural formula for a Cl 2 molecule is drawn as Cl Cl

It is possible to form double and triple covalent bonds.

Double bonds

10

Cl

Cl Cl

One shared pair of electrons is called a covalent bond.

O O

Oxygen atom Oxygen atom Oxygen molecule (O 2)(6 outer electrons) (6 outer electrons) (each atom now has 8 outer electrons)

The full structural formula for the oxygen molecule O 2 is O O

Triple Bonds

Nitrogen atom Nitrogen atom Nitrogen molecule (N 2)(5 outer electrons) (5 outer electrons) (each atom now has 8 outer electrons)

The full structural formula for the nitrogen molecule N 2 is N N

This contain triple covalent bond.

11

O O

N N N N

Compounds . We can apply the same rules to covalent compounds.

Hydrogen chloride

Hydrogen atom Chlorine atom Hydrogen chloride 1 outer electron 7 outer electrons molecule (HCl)

Each atom in a hydrogen chloride molecule has a full outer shell.

The hydrogen atom has 2 outer electrons like the noble gas helium.The chlorine atom has 8 outer electrons like the noble gas argon.

Covalent molecules can be made from more than two atoms.

Water (H2O)

H O

Hydrogen has 1 outer electron Oxygen has 6 outer electrons12

ClHH Cl+

Covalent bond

It needs to obtain 1 more electron It needs to obtain 2 more electrons

The solution is for the oxygen atom to share its electrons with 2 hydrogen atoms.

O H

H

The full structural formula for H2O is O H

H

Covalent BondsCovalent bonds hold the atoms in a molecule together.

Take Hydrogen (H2) as an example.

Each hydrogen atom has 1 positive proton in the nucleus and 1 negative electron in its electron shell. Two hydrogen atoms share their outer electron to obtain a full outer shell.

- + +

-

The negatively charged electrons are attracted to both positively charged nuclei and this holds the atoms together.

13

Formulae

The number of electrons which an atom needs is called its valency.This tells us the number of covalent bonds that it will form.

Using this we can work out the full structural formula

For example: Water

Hydrogen has 1 outer electron; it needs 1 more outer electron and so forms 1 bond.Oxygen has 6 outer electrons; it needs 2 more outer electrons and so forms 2 bonds.

We therefore draw the full structural formula O H

HAs all elements in the same group of the periodic table have the same number of outer electrons we can save time by looking at the group

Group Group 4 Group 5 Group 6 Group7Number of outer electrons 4 5 6 7Valency (Number of electrons needed ) 4 3 2 1Number of bonds formed 4 3 2 1

For example Phosphorus chlorideElement Phosphorus (P) Chlorine (Cl)Group 5 7

14

Number of outer electrons 5 7Valency (Number of electrons needed ) 3 1Number of bonds formed 3 1

Full structural formula Cl P Cl

ClFor example carbon sulphide

Element Carbon (C) Sulphur (S)Group 4 6Number of outer electrons 4 6Valency (Number of electrons needed ) 4 2Number of bonds formed 4 2

Full structural formula S C S

Working out molecular formulae

Molecular formulae use symbols to show the number of each atom in a molecule. We can deduce the molecular formula from the structural formula or work it out using the valencies.

Example Phosphorus Chloride

Symbols P ClValency 3 1Swap 1 3Formula P1 Cl3

The formula for phosphorus chloride is PCl3

Sometimes you will need to simplify the formulae.Example Carbon sulphide

Symbols C SValency 4 2Swap 2 4Simplify 1 2Formula C1 S2

The formula for carbon sulphide is CS2

15

As Carbon sulphide would work out as C2S4

This is simplified to CS2 to get the correct number of atoms as show by the full structural formula; S C S

Compounds which do not obey the rules.

Some covalent compounds do not obey the valency rules.The names of these compounds tell us the molecular formulae.

eg In the compound carbon dioxide, the prefix di means two. So the compound contains one carbon and two oxygen atoms.The molecular formula is CO2

Prefixes in compound names are:mono = 1di = 2tri = 3tetra = 4penta = 5

Examples of compounds where the name tells us the formula are:

carbon monoxide CO

nitrogen dioxide NO2

sulphur trioxide SO3

dinitrogen tetraoxide N2O4

16

(note in these formulae we do not simplify)

Shapes of covalent molecules

The electrons in the first electron shell are found in a sphere but the other electron shells actually hold the electrons in four orbitals.

Thus hydrogen and oxygen which we represent as;

H O

Should really be represented as

This would give us the molecule water drawn as:

17

and

We do not have to use orbitals when we show how molecules form, however it is important when working out the actual shape of molecules

Each orbital can hold two electrons giving the 8 outer electrons which atoms need to have a stable outer shell.

When molecules form, the orbital’s overlap and gives us one of four possible shapes.

The shape depends on the number of bonds formed between the atoms.

Number of Bonds Shape Name of shape

18

1

2

3

Linear

Angular

Pyramidal

H F

Covalent Molecules and Covalent Networks

Covalent substances can be divided into two groups depending on their structure.

Covalent molecules

So far we have only considered covalent molecules where the molecular formula tells us the exact number of atoms in a molecule.

eg water H2O A molecule of water has 1 oxygen atom joined to two hydrogen atoms.

Covalent networks

A few covalent substances have their atoms joined into a huge network.

19

4

Tetrahedral

e.g. diamond (carbon) (C) and silicon dioxide (SiO2)

These substances will contain many millions of atoms. Their formulae do not tell us the number of each atom but the ratio of the atoms.e.g. The formula for silicon dioxide is SiO2.

This does not mean that the silicon dioxide network contains 1 silicon atom joined to 2 oxygen atoms.

It means the ratio of Si : O is 1:2

i.e. there are twice as many oxygen atoms as silicon atoms.

IonsAtoms of the same element always have the number of protons but the number of electrons can change when a compound is formed. This gives the atom a charge and we call it an ion.

Metal atoms form positive ions

Non-metal atoms form negative ions.

Positive and negative ions are found together in some compounds.

A positive ion is made when an atom loses electronsA negative ion is made when an atom gains electrons.

For example:

Atom Symbol Electrons Lost or Gained Ion formedNa 1 electron lost Na +

Al 3 electrons lost Al 3+

Cl 1 electron gained Cl -

20

O 2 electrons gained O 2-

What information do we get from an ion symbol?

Here is a symbol for the magnesium atom.

Mass number 25 Mg

Atomic number 12

This magnesium atom contains :- 12 protons13 neutrons12 electrons

Here is a symbol for the magnesium ion.

Mass number 25 Mg 2+ Electric charge (for ions only)

Atomic number 12

magnesium ion contains :- 12 protons13 neutrons10 electrons

Note: in an ion the number of protons is not equal to the number of electrons.

Ionic Bonding (metal / non-metal)

In order to become stable elements want the stable electron arrangement as their nearest Noble gas (8 Outer electrons, 2 for Li & Be)

Elements can also obtain the stable electron arrangement of the noble gases by forming charged particles called IONS.

Metal atoms form positive ions by losing electrons.

sodium atom sodium ion Na Na+ + e-

Electron 2,8,1 2,8,arrangement

number of positive charges = number of electrons lost

21

Na Na+

loses 1 e

Na+

= periodic table group number

Non-metal atoms form negative ions by gaining electrons.

gains 1 e

e.g. chlorine atom chloride ionCl + e- Cl-

Electron 2,8,7 2,8,8arrangement

number of = number ofnegative charges electrons gained

For exampleMagnesium atom loses 2 e to form a Magnesium ionMg Mg 2 ++ 2 e2,8,8,2 2,8,8,

and

Sulphur atom gains 2e to form a Sulphide ionS + 2e S 2 -

2,6 2,8,

Note : The names of the non-metals change to have the ending ‘ –ide ‘ when an ion is formed.

Transition metal ions

The charge on the metal ion is shown by a Roman number after the name,

e.g. an iron (III) ion is Fe3+ a copper (II) ion is Cu2+

22

Cl Cl-

These types of equations are known as an ion-electron equations and can be written for the formation of any simple ion.

Complex ions

Some atoms form groups of atoms which have an overall charge. These are listed on page 4 of the data book.e.g. sulphate SO4

2-

nitrate NO3 -

The names of these ions usually end in ‘ ate ‘ or ‘ ite ‘ and contain oxygen.

Ionic Compounds (Metal/ Non-metal)

We know: metals become stable by losing electrons Non-metals become stable by gaining electrons

Ionic compounds are formed when metals transfer their outer electrons to the non-metals.

Eg Sodium wants to lose 1 electron and Chlorine wants to gain 1 electron

Na atom Cl atom2,8,1 2,8,7

1 electron transferred

Na+ ion Cl- ion2,8, 2,8,8,

Sodium chloride Na+ Cl- 23

Eg Calcium wants to lose 2 electrons and Chlorine wants to gain 1 electronCa atom Cl atom Cl atom2,8,8,2 2,8,7 2,8,7

1 electron transferred

1 electron transferred

Ca2+ ion Cl- ion Cl- ion2,8,8, 2,8,8, 2,8,8,

Calcium chloride Ca2+ (Cl-)2

Formulae of ionic compounds e.g. aluminium oxide iron (III) bromide copper (II) nitrate

a) Al O Fe Br Cu NO3-

V 3 2 3 1 2 1S 2 3 1 3 1 2S 2 3 1 3 1 2F Al2O3 FeBr3 Cu(NO3)2

Note;i) The valency is obtained from the group in the periodic table;

Group 1 2 3 4 5 6 7 8

Valency 1 2 3 4 3 2 1 0

ii) metals give positive ions.non-metals give negative ions.

therefore; Group 1 2 3 4 5 6 7 8

24

Valency 1+ 2+ 3+ 4+/- 3- 2- 1- 0

iii) The valency of transition metals is given in roman numerals. If it is not given Assume: silver valency (I)

All other transition metals valency (II)

iv) Complex ions are obtained from the data book page 4.Complex ions are identified by the name not ending in –ide.The exceptions are hydroxide (OH-) and ammonium (NH4

+).

STRUCTURE OF COMPOUNDS

Ionic compounds form a neat array oppositely charged ions.

e.g. sodium chloride Na+ Cl-

25

This structure is called an Ionic lattice (sometimes a crystal lattice).

The attractions between oppositely charged ions are very strong and difficult to break..

An Ionic formula does not tell use the actual number of ions present.

It tells us the ratio of ions

i.e. Na+ Cl- is 1:1

for every one Na+ ion there is one Cl- ion.

Acids and Bases

The pH Scale

A continuous scale from below 0 to above 14 It is a measure of the hydrogen ion (H+) concentration of a solution

Dissociation of Water

Water exists as an equilibrium between water molecules and hydrogen and hydroxide ions

26

H2O (l) ⇌ H + (aq) + OH – (aq) molecules ions

In water equilibrium lies over to the left – mainly exists as

pH OH- versus H+ Examples

Acidic pH less than 7concentration of

H+ > OH-

Hydrochloric acid, Nitric acid,

Sulphuric acid

Neutral pH = 7concentration of

H+ = OH-

Water, Sugar solution,

salt solution

Alkaline pH more than 7concentration of

H+ < OH-

Sodium hydroxide, Potassium hydroxide

Bases/Alkalis

A base is a substance that neutralises and acid (brings the pH of the acid up to 7 ).

An alkali is a base which is soluble in water.

Making Acids or Alkalis Acids

Acids are made by dissolving soluble non-metal oxides in water.

o These make acidic solutions by raising the H+ concentration of watero CO2 (forms carbonic acid, H2CO3 when dissolved in water)o NO2 (forms nitric acid, HNO3 when dissolved in water)

Alkalis Alkalis can be made by dissolving soluble metal oxides in water to make metal hydroxides - (see data book). For example:

27

In water and other neutral solutions (pH 7)

the concentration of H+ = the concentration of OH-

Na2O + H2O 2 NaOHo This makes an alkaline solution because it raises the OH- concentration of the

watero Common bases are metal oxides, metal hydroxides or metal carbonates. For

example: Na2O Na2OH Na2CO3

Neutral Insoluble oxides will not affect the pH of water. They will not lower or raise the pH of water from 7 because they do not dissolve into the water.Common acids and alkalis used in the laboratory

Common Laboratory Acidshydrochloric HClnitric HNO3

sulphuric H2SO4

ethanoic CH3COOH

Common Laboratory Basessodium hydroxide NaOHPotassium hydroxide KOHcalcium hydroxide Ca(OH)2

ammonia NH3

Dilution of acids and alkalis

Acids Acids have a pH below 7, which means that they have more H+ than OH-. Diluting an acid, increases the pH towards 7 (concentration of H+ decreases)

Alkalis

Alkalis have above 7, which means that they have more OH- than H+.

28

Diluting an alkali, decreases the pH towards 7 (concentration of OH- decreases)

Neutralisation (Salt Preparation)Neutralisation is the reaction of acids with bases in which salt and water are produced.

Base – a substance that reacts with an acid to neutralise it eg metal oxide, metal hydroxide or metal carbonate

Salt – a substance in which the hydrogen ion of an acid has been replaced by a metal or ammonium ion

During a neutralisation the pH of the resulting solution is pH 7

This can easily been seen by using an indicator.

Neutralisation Reaction Equations

Acid + Base Salt + Water

29

Acid + metal oxide salt + H2O

Acid + metal hydroxide salt + H2O(alkali)

Acid + metal carbonate salt + H2O + CO2

Naming of Salts

The name metal in the base appears in the name of the salt eg copper (II) carbonate produces a copper (II) salt

The name of the negative ion in the acid appears in the name of the salt

acid negative ion name of saltHydrochloric Chloride ChlorideNitric Nitrate NitrateSulphuric Sulphate Sulphate

Examples:

nitric acid + iron (II) oxide iron (II) nitrate + water

HNO3 + FeO Fe(NO3)2 + H2O

hydrochloric + copper (II) copper (II) + water acid hydroxide chloride

HCl + Cu(OH)2 CuCl2 + H2O

sulphuric + calcium calcium + water + carbon acid carbonate sulphate dioxide

H2SO4 + CaCO3 CaSO4 + H2O + CO2

30

Neutralisation reactions

In neutralisation reactions the hydrogen ions from the acid are reacting with ions from the base to form water molecules.

This can be seen by omitting the spectator ions, (the ions which do not change during the reaction).

For example when hydrochloric acid is neutralised by sodium hydroxide we can see what is happening by following 4 steps.

1. Write a balanced equation including state symbols

2HCl(aq) + NaOH(aq) NaCl(aq) + H2O (l)

2. Rewrite including ionic formulae for underlined substances

H+Cl- (aq) + Na+OH- Na+Cl- (aq) + H2O(l)

3. Identify the ions which do not change -Spectator Ions

H+Cl- (aq) + Na+OH- Na+Cl- (aq) + H2O(l) (sodium and chloride ions are the spectator ions in this equation)

4. Rewrite the equation missing out the spectator ions

H+ (aq) + OH- H2O(l)

31

Titrations

A titration is a method of analysis that allows you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration flask.

Neutralisation reactions can be carried out very accurately by using a burette and a pipette in a titration. The volumes obtained can be used to calculate the concentrations of the acid or alkali.

32

Conical flask

Pipette

Pipette Filler

FORMULAE

When determining formula we use valency which we can obtain from the group in the periodic table.

1 2 3 4 5 6 7 8/0 Group 1 2 3 4 5 6 7 0 Valency 1+ 2 + 3+ 4- 3 - 2- 1- 0 Charge

H HeLi Be B C N O F NeNa Mg Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra Ac

Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb LuTh Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

To determine a formula cross over the valences and simplify

e.g. nitrogen fluoride carbon oxidesymbol N F symbol C O

valency 3 1 valency 4 2

Formula N1F3 Formula C2O4

Simplify NF3 Simplify CO2

Ionic FormulaeIn ionic formulae we show the charges.Note

The valency of transition metals is given in roman numerals.

Complex ions are obtained from the data book page 8.

e.g. calcium chloride iron (III) bromide copper (II) nitratea) Ca2+Cl- Fe3+ Br- Cu2+ NO3

-

b) Ca2+ (Cl-)2 Fe3+ (Br-)3 Cu2+ (NO3-)2

33

Formulae: Ca2+(Cl-)2 Fe3+(Br-)3 Cu2+(NO3-)2

What does a formula tell you?

What a formula tells you depends on the structure of a substance.

Covalent molecules

The formula gives the number of atoms present in the molecule>

e.g. H2O contains 2 H atoms and 1 O atom

Covalent Network

The formula gives the simplest ratio of atoms in the substance.

e.g. SiO2 contains Si and O atoms in the ratio 1:2

Ionic LatticeThe formula gives the simplest ratio of ions in the substance.

e.g. Fe3+(Br-)3 contains Fe3+ and Br- ions in the ratio 1:3

34

Balanced equations

In a reactions atoms / ions are not destroyed they just ‘rearrange’ what other atoms / ions they are attached to.

In an equation there must be the same number of each atom/ion on each side of the equation.

For example when magnesium reacts with oxygen gas to form magnesium oxide.

Mg + O2 MgO

There must be two oxygen on the right. For this to be possible we must have 2MgO

Mg + O2 2MgO

For this to be possible we must have started with 2 Mg

2Mg + O2 2MgO

Thus the balanced equation is:

2Mg + O2 2MgO

We describe this as 2 moles of magnesium reacting with 1 mole of oxygen forming 2 molesa of magnesium oxide.

2Mg + O2 2MgO2 mol 1mol 2 mol

35

Mole calculations

Using the data booklet page 7 we can work out the gram formula masses (GFM) of elements and compounds.

GFM is defined as the mass f 1 mole.

Calcium nitrate Ca(NO3)2

6 x O = 6 x 16 = 962 x N = 2 x 14 = 281 x Ca = 1 x 40 = 40

GFM = 144g = 1 mole

Once we know the GFM we can calculate masses and number of moles using the triangle

m Mass

Number of moles n x GFM

What is the mass of 0.1 moles of calcium nitrate?m = n x GFM

= 0.1 x 144g= 14.4g

How many moles of calcium nitrate are there in 72g of calcium nitrate?

n = m/GFM= 72/144= 0.5 moles

36

Calculations from balanced equations

To do this use the following technique:Here are the steps to carry out:

1. Put a ? over what you need to calculate.

2. Put a over what you know about.

3. Use the balanced equation to write mole ratio.

4. Calculate the mass of each substance

5. Using what you actually have calculate what you want to know

What mass of MgO will be formed when 98g of Mg is burned in excess oxygen? √ ?2Mg + O2 2MgO

Mole ratio 2 mol 2 mol2(24.5) 2(24.5 + 16) 49g 81g

Actually have 98g 98 x 8149

= 162g

37

Concentration of Solutions

Concentrations are expressed as the number of moles of a substance dissolved in 1 litre of water. (mol l-1).We use the triangleOnce we know the GFM we can calculate masses and number of moles using the triangle

n number of moles

concentration c x V volume (in litres) (mol l-1)

What is the concentration if 0.1 moles of calcium nitrate is dissolved in 250cm3 of water?c = n / V 250 cm3 = 250/1000 l = 0.25 l

= 0.1 / 0.25= 0.4 mol l-1

What mass of Calcium nitrate is needed to make 100cm3 of a 0.1 mol l-1 solution?

m = n x GFM We work out GFM from the formula as shown above.= n x 144g To calculate n we use: n = c x v= n x 144g = 0.1 x v v = 100cm3

= 0.01 x 144 = 100/1000 l = 1.44g = 0.1 l = 0.1 x 0.1 = 0.01 mol

38

Calculations for titrations

To do this use the following technique:Here are the steps to carry out:

1. Put a ? over what you need to calculate.

2. Put a over what you know about.

3. Use the balanced equation to write mole ratio.

4. Calculate the number of moles you actually have of the substance you know about

5. Use the mole ratio to get the number of moles of the substance asked about.

6. Calculate the answer to the questionRemember to turn all volume into litre by dividing cm3 by 1000.i.e. 20cm3 = 20/1000 = 0.020 litres

ExampleIf 20cm3 of NaOH is neutralised by 20cm3 of 1 mol l-1 H2SO4, what is the concentration of the NaOH?

√ ?H2SO4 + 2NaOH Na2SO4+2H2O

Mole ratio 1 mol 2 mol Actually have c =1 mol l-1 v = 20cm3 = 0.020 litre v = 20cm3 = 0.020 litre c = ?

n = 1 x 0.02 c = n/v = 0.02 mol 0.04 mol

C = n/v = 0.04 / 0.02 = 2 mol l-1

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Unit 2

Hydrocarbons.

Burning hydrocarbons always produces carbon dioxide and water.

Results U-tube Boiling tubeColourless liquid condensed Lime water turns cloudyCobalt chloride paper changes from blue to pink.

Conclusion Water present Carbon dioxide present

This tells us that hydrocarbons contain Carbon : because carbon dioxide is madeHydrogen: because water is made

It does not tell us that they contain oxygen because the oxygen in carbon dioxide and water can have come from the air on burning.

Word Equation :

methane + oxygen → carbon dioxide + water

Formula equation :

CH4 + 2O2 → CO2 + 2H2O

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Measuring the Energy

The energy produced when a fuel is burned is calculated using the equation:

Eh = cmΔTwhere Eh = energy gained by the water

c = specific heat capacity of water = 4.18 kJ0C-1kg-1

m = mass of water (1 litre = 1kg) ΔT= change in temperature of water

For example when 200cm3 of water is heated from 20oC to 50oC using the following apparatus.

  

c = specific heat capacity of water = 4.18 kJ0C-1kg-1

m = 200 / 1000 = 0.2kgΔT= 50 – 20 = 30oC

Eh = 4.18 x 0.2 x 30 = 25.08 kJAs the reaction is exothermic we write:

Eh = - 25.08kJ

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Hydrocarbons

Hydrocarbons are molecules containing hydrogen and carbon only

Carbon – always forms 4 bondsHydrogen - - always forms 1bond

The hydrocarbons are grouped into families called Homologous series.

Homologous Series- A group of hydrocarbons with:

Similar chemical properties

Same General Formula

42

Alkanes General formula CnH 2n+2

Structural FormulaMethane H CH4

H C H

HEthane H H C2H6

H C C H

H H

Propane H H H C3H8

H C C C H

H H H

Note: the bonds between the atoms are covalent single bonds

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C8H188Octane

C7H167Heptane

C6H146Hexane

C5H125Pentane

C4H104Butane

C3H83Propane

C2H62Ethane

CH41Methane

Molecular formulaNo. of Carbon atomsName

Alkenes

General Formula CnH2n

Ethene H H C2H4

H C C H

Propene H H H C3H6

H C C C H

H

Note: Alkenes contain a double bond (C=C).

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C6H126Hexene

C5H105Pentene

C4H84Butene

C3H63Propene

C2H42Ethene

Molecular FormulaNo. of Carbon AtomsAlkene

Cyclo alkanes

General Formula CnH 2n

Cyclopropane H C H C3H6

H C C H

H H

Cyclobutane H H C4H8

H C C H

H C C H

H H

Saturated or unsaturated hydrocarbons.45

C6H126CyclohexaneC5H105CyclopentaneC4H84CyclobutaneC3H63Cyclopropane

Molecular formulaNumber of Carbon atoms

Alkane

Alkanes and cycloalkanes are saturated because all the (C-C) bonds are single bonds.

Alkenes are unsaturated because they contain a (C=C) double bond..

The double bond is responsible for the quick reaction with bromine water.

Bromine can be used to tell the difference between saturated and unsaturated hydrocarbons.

Addition Reactions The bromine adds to the alkene across the double bond.

The reaction involves the breaking of the carbon-carbon double bond to form a carbon-carbon single bond.

C3H6 + Br2 C3H6Br2

Changing Alkenes to Alkane

Alkenes can react with Hydrogen under certain conditions to form Alkanes.

Ethene + Hydrogen EthaneC2H4 + H2 C2H6

Propene + Hydrogen PropaneC3H6 + H2 C3H8

Isomers 46

C CH

HH

H

BrBr+ C CH HHH

BrBr

Isomers: same molecular formula but different structural formula.

Butane – formula is C4H10 and there are two different structures.

This is a straight chain molecule. This is a branched chain molecule.

For the molecule C4H8

Cyclobutane Butene

Naming Alkanes

47

C C

H

H

HH

H

C C

H

HH

CC

CCH H

HH

HH

H H

C CH

H

HHH

HC

HC HH

C CH

H

HHH

H

C

HHC

H

H

Identify the longest chain.Number the carbon atoms to place the branch on the lowest number possible.Identify the position of the chains.Identify the number of each branch.

2,3,4-trimethylpentane

Naming Alkenes

This is similar to alkanes but th position of the double bond must be as low as possible

.

3 – methybut – 1 – ene

Alkanols (alcohols)General formula CnH2n+1OH

Alkanols contain the functional group –OH (hydroxyl)

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C8H17OH8Octanol

C7H15OH7Heptanol

C6H13OH6Hexanol

C5H11OH5Pentanol

C4H9OH4Butanol

C3H7OH3Propanol

C2H5OH2Ethanol

CH3OH1Methanol

Molecular formulaNo. of Carbon atomsName

Structural FormulaMethanol H CH3OH

H C OH

HEthanol H H C2H5OH

H C C OH (CH3CH2OH)

H H

Propanol H H H C3H7OH

H C C C O H (CH3CH2CH2OH)

H H H

Naming alkanols

Alkanols are named like the alkenes but here the number of the hydroxyl group (-OH) must be as low as possible.

 

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Butan-1-ol

Butan-2-ol

Uses of Alkanols (alcohols) Alcoholic Drinks. Ethanol is found in alcoholic drinks. FuelsAlcohols burn very easily with a clean flame and so they can be used as a fuel.

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The products of combustion are carbon dioxide and water.

C2H5OH + 3O2 2CO2 + 3H2O

Ethanol can be used as a petrol replacement.Methanol is used as the fuel for drag racers.

CH3OH + 1½ O2 CO2 + 2H2O 

SolventsAlkanols are good solvents for many types of substances.

The carbon chain helps alkanols dissolve in covalent substances The hydroxyl group (-OH) helps alkanols dissolve in water. Ethanol is used as a solvent in perfumes, aftershave and mouthwash as it is good at dissolving and evaporates easily as well.

 Alkanoic acids (carboxylic acids)

General formula CnH2n+1COOH

Alkanoic acids contain the functional group –COOH (carboxyl)

O

C OH

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C7H15COOH8Octanoic

C6H13COOH7Heptanoic

C5H11COOH6Hexanoic

C4H9COOH5Pentanoic

C3H7COOH4Butanoic

C2H5COOH3Propanoic

CH3COOH2Ethanoic

HCOOH1Methanoic

Molecular formulaNo. of Carbon atomsName

Be careful when writing the molecular formula or naming alkanoic acids. The stem will have 1 carbon less than you expect as it also contains the carboxyl group COOH.

i.e. C4H9COOH is pentanoic acid as there are 5 carbon atoms in this alkanoic acid.

Structural FormulaMethanoic acid O HCOOH

H C OH

Ethaoic acid H O CH3COOH

H C C OH

H

Propanoic acid H H O C2H5COOH

H C C C O H (CH3CH2COOH)

H H 52

Uses of Alkanoic acids (carboxylic acids) food preservatives (i.e. vinegar is a solution of ethanoic acid used for pickled onions)

 cleaning products and descaling agents (i.e. vinegar in solutions for washing windows)

 manufacture of esters and plastics

Esters

Esters are made by reacting alkanols with alkanoic acids.

Uses of EstersFood flavouringsEsters are added to foods as their smell influences the flavour, for example pineapple cubes contain methyl butanoate

Fragrances. The smells of specific esters allows them to be used in things such as perfumes and air fresheners.

Solvents.Many esters are sold to remove stains from clothes and house furnishings.

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MaterialsPolyesters are esters used in clothing and fabrics such as nylon.

POLYMERS

Polymers are macromolecules (big molecules).

Monomers are the small molecules that combine to form a polymer.

A polymer is the large molecule formed by combining many monomers

Polymers are very large molecules containing many repeating units.

Plastics are made by a process called polymerisation of which there are two types:

Addition polymerisation54

Condensation polymerisation

Addition polymerisation.

Addition polymers are made from alkenes

The names of polymers come from the name of the monomer

Propene makes poly(propene)

Chloroethene makes poly(chloroethene)

Ethene makes poly(ethene)

The monomer for poly(ethene) is ethene.

This is an unsaturated molecule containing a carbon to carbon double bond, which makes the ethene molecule reactive.

55

The double bond splits open leaving free bonds to join onto other molecules forming a long chain.

Butene can also be used to make a polymer, called poly(butene.)

To make things easier the molecule is drawnin the shape of a letter H

Since addition polymers are formed by opening a C=C and joining to give a chain they have nothing but carbon atoms in the main chain.

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EtheneRepeating unit

Poly(ethene)

Butene Repeating unit Poly(butene)

Condensation polymerisation.

In condensation polymerisation many small molecules combine to form a polymer.

In condensation polymerisation molecules are joined together by removing water.

Polyesters are formed by condensation polymerisation from:alcohols with two hydroxyl groups (–OH)

and carboxylic acids with two carboxyl groups (–COOH)

This means that the polyester molecules can continue to grow in both directions with many ester linkages.

57

In order to obtain the structures of the monomers used to make the polyester:

1. Locate the ester link:

2. Water adds on like this:

O H

H

3. The carboxyl and hydroxyl groups in the monomers can now be formed:

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C

O

O

C

O

O

Natural Polymers

Many addition and condensation polymers are made by the chemical industry; however, polymers are found in nature in both plants and animals.

Starch is a natural condensation polymer made from glucose in plants.

Proteins are also natural condensation polymers.

They are the major structural material of plant and animal tissue e.g. muscles, skin, hair and are

involved in the maintenance and regulation of life processes.

Unit 2Metals

Metals conduct electricity because they have a sea of delocalised electrons.

LEO: Loss Electrons Oxidation

GER: Gain Electrons Reduction

Reactions of metals (OXIDATION)

1. Metals and water.

metal + water metal hydroxide + hydrogen

e.g. potassium + water potassium hydroxide + hydrogen

(formula) 2K + 2H2O 2KOH + H2

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C

O

O H + H O …..

(ionic) 2K + 2H2O 2K+ + 2OH- + H2

2. Metals and acid.

Metals above hydrogen in the electrochemical series react with acids.

metal + acid salt + hydrogen

e.g. magnesium + hydrochloric magnesium + hydrogen acid chloride

(formula) Mg + 2HCl MgCl2 + H2

(ionic) Mg + 2H+ + 2Cl- Mg2+ + 2Cl- + H2

3. Metals and oxygen metal + oxygen metal oxide

e.g. magnesium + oxygen magnesium oxide

(formula) 2Mg(s) + O2(g) 2MgO(s)

(ionic) 2Mg(s)) + O2(g) 2Mg2+O2- (s)

4. The Reactivity Series

These reactions give an indication of the reactivity of the metal and are summarised below. This is called the reactivity series.

Metal Reaction with

Oxygen Water Acid

Potassium React React

Sodium React forming

Lithium metal hydroxide forming

Calcium to and hydrogen

Magnesium react salt

Aluminium with

Zinc form steam and

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Iron

Tin metal oxide hydrogen

Lead

Copper No

Mercury No

Silver No Reaction Reaction

Gold Reaction

Extracting metals from compounds (REDUCTION)Metals are found as compounds called ores.The more reactive metals form the most stable ores and so are hardest to obtain.

5. Methods of extraction.

Heating metal oxides

The least reactive metals can be obtained from their ores simply by heating

Metal oxide metal + oxygen

e.g. mercury oxide mercury + oxygen

2HgO 2Hg + O2

Heating metal oxides with carbon

More reactive metals are extracted using carbon to remove the oxygen.

Metal oxide + carbon metal + carbon dioxide

e.g. lead oxide + carbon lead + carbon dioxide

PbO2 + C Pb + CO2

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Electrolysis

Electricity is needed to obtain the most active metals from their compounds.

e.g. aluminium oxide aluminium + oxygen

2Al2O3 4Al + 3O2

(Al3+)2(O2-)3 4Al + 3O2

Al3+ + 3e- Al Reduction

More about Electrolysis

For electrolysis to happen the ionic lattice must be broken down by dissolving or melting the compound. This makes the ions free to move and so carry the current.

e.g. Electrolysis of molten lead (II) bromide- Pb2+(Br-)2 (l)

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Product at the negative electrode

Product at the positive electrode

molten lead (II) bromide

lead bromine

At the negative electrode : Pb 2+ (aq) + 2e → Pb (s) (metal ions gain electrons)

At the positive electrode : 2Br –

(aq) → Br2 (g) + 2e(non-metal ions lose electrons)

6. Percentage of Metal in an Ore.

Step 1 Calculate the gram formula mass (gfm)

K2CO3 - potassium carbonate3 x 16 = 481 x 12 = 122 x 39 = 78

= 138g

Step 2 Calculate the total mass of the metal in the formula

K 3 x 39 = 78g

Step 3 Divide the mass of the metal by the gfm and multiply by 100%

% mass of the metal = 78 x 100% 138

= 56.5%

Making electricityElectricity is a flow of charged particles: flow of electrons through metals,

flow of ions through solutions or melts.

Electrons always flow from metals high in the electrochemical series through the wires to metals lower in the electrochemical series.

The further apart two metals are in the electrochemical series the larger the voltage obtained.

.

2.7V 1.1V

Mg Cu Zn Cu

electrolyte

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Redox & Displacement

When electrons go into an electrode we get REDUCTIONWhen electrons leave an electrode we get OXIDATION

Electron flow

V

Zn Ion Bridge Cu

Zn2+SO42- Cu2+SO4

2-

The copper ions in the solution accept these electrons and turn into copper metal.

Zn Zn2+ + 2e- oxidationCu2+ + 2e- Cu reduction

The oxidation and reduction equations can be combined to form what is known as a redox equation

e.g. Zn + Cu2+ Zn2+ + Cu redox

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Cells involving non-metals.

The electrochemical series in the data book has some reactions that involve non-metals

V

Zn Ion Bridge C

Zn2+SO42- I2 / K+I-

If we are told that the following reaction occurs:

I2 + 2e- 2I-

This is Reduction which is where electrons go into an electrode.

So electrons must be going in at the C electrode.

This means that electrons must be leaving at the Zn electrode (Oxidation)

Zn Zn2+ + 2e- reduction

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So electrons must be flowing from the Zinc to the carbon.

Electron flow

V

Zn Ion Bridge C

Zn2+SO42- I2 / K+I-

The diagram shows that electrons flow from zinc metal to the carbon rod and the reactions are shown below:

Zn Zn2+ + 2e- reductionI2 + 2e- 2I- oxidation

The redox equation will be:

I2 + Zn 2I- + Zn2+ redox

Displacement

Metals can displace ions of a less reactive metal.

For example:

Zn(s) + Cu2+SO42- Cu(s) + Zn2+SO4

2-

Omitting the sulphate ions (SO42-) and the state symbols makes the process clearer.

Zn + Cu2+ Cu + Zn2+

Being the more reactive metal the zinc metal is losing its electrons which it gives to the copper ions..

Zn Zn2+ + 2 e- oxidation

Cu2+ + 2e- Cu reduction

Adding the oxidation and reduction equations together gives us the redox equation

Zn + Cu2+ Cu + Zn2+ redox

Metals reacting with acids is an example of a displacement reaction.

Zn(s) + (H+)2SO42- Zn2+SO4

2- + H2

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The zinc metal is displacing the hydrogen ions.

The metals which do not react with acids, can not displace the hydrogen ions and so these metals must be less reactive than hydrogen.

Therefore hydrogen is put into the reactivity series between lead and copper.

The process of losing electrons is called oxidation and that of gaining electrons is called reduction.

Fuel Cells & Rechargeable Batteries .

A fuel cell is a device that converts chemical energy from a fuel such as hydrogen into electrical energy through a chemical reaction with oxygen or some other oxidising agent (a substance that causes oxidation)

FertilisersFertilisers contain the essential elements (NPK) that plants need.

Examples are ammonium salts (such as NH4Cl),

nitrates (such as KNO3)

potassium salts (such as K2SO4)

phosphates (such as K3PO4)

Percentage composition Fertilisers need to contain different proportions of N : P : K for different plants.

When comparing fertilisers it is useful to know the percentage of an element in that fertiliser. To calculate the percentage of nitrogen in ammonium nitrate we first calculate the GFM

NH4NO3

3 x 0 = 3 x 16 = 481 x N = 1 x 14 = 144 x H = 4 x 1 = 41 X N = 1 X 14 = 14

GFM = 80 gFrom the total number of nitrogen atoms in ammonium nitrate calculate the total mass of nitrogen.

67

There are 2 nitrogen atoms in the formula therefore total mass nitrogen = 14 + 14 = 28

Percentage nitrogen = mass of nitrogen x 100 = 28 x 100 =35% GFM 80

Making fertilisers

Making Fertilisers by Neutralisation

Nitrate fertilisers are formed using nitric acid:

HNO3 + NaOH NaNO3 + H2O

Phosphate fertilisers are formed using phosphoric acid:

H3PO4 + 3NH3 (NH4)3PO4

For fertilisers containing potassium, an acid is reacted with a potassium compound:

K2CO3 + HNO3 KNO3 + H2O + CO2

Ammonium fertilisers are formed using ammonia and nitric acid:

NH3 + HNO3 NH4NO3

The Haber Process

To make ammonium nitrate we need ammonia and nitric acid.

68

To make nitric acid we need ammonia so the production of ammonia is essential to making ammonium nitrate.

Ammonia is formed by reacting nitrogen (from air) and Hydrogen (from natural gas).

Iron is used as a catalyst and he reaction is carried out at 400oC.

N2(g) + H2(g) NH3(g)

 The reaction is reversible i.e. it can go in both directions.

To help stop this, the ammonia is cooled down to turn it into a liquid.

Any unreacted nitrogen and hydrogen is recycled.

Unreacted N2 and H2 recycled

N2/H2/NH3

liquid NH3

The ammonia is then used to make nitric acid.

NUCLEAR CHEMISTRY

Types of radiation

There are 3 types of radiation, alpha ( ), beta ( ) and gamma ( ). Their properties can be studied using an electrical field.

-

α γ

β

+

69

Nitrogen

Hydrogen

Reaction ChamberFe catalyst400 0C200 atm

Cooler

α β γ

paper 2cm Al 5cm concrete

Alpha particles

Alpha radiation consists of helium nuclei,

Alpha can only travel a few centimetres.

Beta particles

A beta particle is an electron, .

Beta can travel metres.

Gamma waves

Gamma waves are electronegative waves.

They can travel 100’s of metres.

Nuclear equationsIn nuclear equations, the sum of the atomic number and mass number on each side of the equation should balance.

Alpha emissions

Beta emissions

Half-life

70

The half-life of a radioisotope never changes. It is the time taken for the sample's activity to fall by half.

Example 1

The mass of a radioisotope falls from 1.6g to 0.1g in 2 hours. What is the half-life of this radioisotope?

Answer1.6 g 0.8g 0.4g 0.2g 0.1g

The activity halves 4 times in 2 hoursHalf life = 2/4 = 0.5 hour

Example 2

If a 1g sample of a radioisotope with a half-life of 3 days has an activity of 32 c.p.m., how long would it take for the activity to fall to 8 c.p.m.?

Answer If 1g sample is 32 cpm.

32 cpm 16 cpm 8 cpmActivity halves 2 times.Half life = 3 daysTime taken = 2 x 3 = 6 days

Carbon datingCarbon -14 is present in the atmosphere.

Carbon dioxide is responsible for carbon-14 entering the food chain.

The levels of carbon dioxide in living things stays constant as it is absorbed through photosynthesis or in food, and it decays by beta emission.

When living things die no more carbon-14 is absorbed and as the C-14 continue to decay by beta emission its levels fall.

We can use the half-life of C-14 (5,700 years) to calculate the age of the object.

Example

If a piece of wood has 25 % the radiocativity of a living tree then it has undergone 2 half-lives.100% 50% 25%Half-life = 5700 yearsTree died 2 x 5,700 = 11,400 years ago.

Uses of radioisotopes71

Radioisotopes of elements have a wide variety of uses.

Cobalt-60 Used in medicine to treat cancer..

Iodine-133 Used to treat thyroid gland.

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