Acids, bases and salts

1. Acids and bases Acid

An acid is a substance that produces hydrogen ions when dissolved in watero Has a sour tasteo Turns blue litmus paper redo Turns Universal Indicator red/ orange/ yellow

Base A base is a substance that accepts hydrogen ions when reacting with an acid Alkalis are soluble bases

o Has a bitter taste and soppy feelo Produces hydroxide ions when dissolved in watero Turns Universal Indicator blue/ violet

pH pH of a solution is based on the relative concentration of hydrogen or hydroxide

ions present in the solution The universal indicator is a mixture of dyes that changes color depending on the

pH By comparing against a pH colour chart, the hydrogen/ hydroxide ions

concentration or relative acidity/ alkalinity can be determined Strength of acid

A strong acid completely dissociates when dissolved in water to produce hydrogen ions

A weak acid partially dissociates when dissolved in water to produce hydrogen ions, leaving some acid molecules undissociated in the solution

Reaction of acids React with metals to from hydrogen and a salt

o Metal + acid salt + hydrogen React with carbonates to form a salt, carbon dioxide and water

o Carbonate + acid salt + water + carbon dioxide React with bases to from a salt and water (neutralization)

o Base + acid salt + watero Ionic : H+ + OH- H2O

Uses of acids Sulfuric acid

o Make detergentso Make fertilizerso Used in car batteries

Reaction of bases

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React with acids to from a salt and water (neutralization)o Base + acid salt + watero Ionic : H+ + OH- H2O

React with ammonium salts, when heated, to produce ammonia gas and salto Alkali + ammonium salt ammonia + water + salt

pH of soils They affect the growth and development of plants

o Too acidic soil would prevent plant growth pH controlled by adding bases, like quicklime (calcium oxide) and slaked lime

(calcium hydroxide), to raise the pH of acidic soilso Alkalis/ aqueous alkalis are not used as they seep into the soil as raise

the ph by too much Oxides

Acidico Are non-metal oxideso Most dissolve readily in water to give acidso React with alkalis to give salt and watero Uses of sulfur dioxide

As a beaching agent in manufacturing of paper (bleaches wood pulp)

As a food preservative, as it is a disinfectant (Kills bacteria) Basic

o Are metal oxideso Most are insoluble in water. Those that do are called alkaliso Solids at room temperatureo React with acids to give salt and water

Amphoterico Are metallic oxides that react with both acids and bases to from salts

and water Aluminum, Lead(II), Zinc

Neutralo Are non-metal oxides that do not react with acids or baseso Are insoluble in watero Water, Carbon monoxide, Nitrogen monoxide

2. Salts Salts are ionic compounds that is formed when a metallic/ ammonium ions replaces one

or more hydrogen ions of a acid (when acid reacts with base) Preparation of salts

Precipitationo Used to prepare insoluble salts

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o React two soluble reactants with desired cation and aniono Filter and wash with distilled water to obtain the salt

Acid neutralizationo Used to prepare soluble salts (not Group 1 or ammonium salts)o React an acid with excess metal/ carbonates/ baseo Filter the mixture, collecting the filtrateo Obtain the salt by crystallisation

Titrationo Used to prepare Group 1 and ammonium saltso Place a fixed volume of acid in a conical flask, and some alkali in a

burette.o Add indicator to acid and add alkali drop by drop, while swirling the

flask, till the indicator just changes colouro Record the volume of alkali needed, and repeat without indicatoro Obtain salt by crystallisation

Solubility of salts All nitrates are soluble All chloride, except silver and lead, are soluble All sulfates, except calcium, barium and lead, are soluble All hydroxides/ oxides, except Group1, ammonium, aluminum, barium and

calcium , are insoluble All carbonates, except Group1 and ammonium, are insoluble

3. Ammonia Manufacture of ammonia

Nitrogen, from fractional distillation of liquid air, and hydrogen, from cracking of crude oil, are needed

They react in a reversible reactiono N2 + 3 H2 2 NH3

o A reversible reaction means that the forward and reversed reaction are occurring simultaneously , until the equilibrium mixture of reactants and products is reached

Conditions 450oC, 250 atm, catalyst of finely divided iron Increase in temperature lowers yield, increase rate Increase in pressure increases both yield and rate

Displacement of ammonia Ammonia gas is produced when heating an ammonium salt with a base

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