IGCSE science Chemistry study notes

C8- Acids, bases and salts

Describe the preparation, separation and purification of salts using techniques specified in Section C2 and the reactions specified in Section C8.1

Preparation: Mixing together elements and compounds. For an aqueous solution, add water.

Separation and purification:
- Distillation. Salty water is heated so that the water evaporates and condenses back into water in the condenser, leaving behind the salt in the flask.

- Filtration. Used to separate an insoluble solid from a liquid.

Crystallisation: Evaporating the solution to a much smaller volume and then leaving it to cool. As the solution cools, crystals form and these can be obtained by filtration.

Suggest a method of making a given salt from suitable starting material, given appropriate information

Acid + Alkali -> Salt + Water
Hydrochloric Acid + Sodium Hydroxide -> Sodium Chloride + Water
Hal + NaOH -> NaCl + H2O
Add 30cm^2 of sodium hydroxide to a flask
Add 2 drops of the indicator phenolphthalein
Add the hydrochloric acid to the flask
The solution will turn colorless when neutralized
Heat the solution to evaporate the liquid and obtain the salt
Acid + Metal -> Salt + Hydrogen
Sulphuric Acid + Zinc -> Zinc Sulphate + Hydrogen
H2SO4 + Zn -> ZnSO4 + H2
Add zinc to a flask of the acid
When zinc dissolves, hydrogen bubbles will appear
Filter the solution to remove the excess zinc
Heat the solution to evaporate the liquid and obtain the salt
Acid + Base -> Salt + Water
Sulphuric Acid + Iron (II) Oxide -> Iron Sulphate + Water
H2SO4 + FeO -> FeSO4 + H2O
Add and excess iron oxide to the sulphuric acid
Filter the solution to remove the excess iron oxide
Heat the solution to evaporate the liquid and obtain the salt

Describe the following tests to identify aqueous cations

Ammonium -> Add dilute sodium hydroxide, warm up -> Ammonia gas is released, damp red litmus paper turns blue
Copper (II) -> Add dilute sodium hydroxide or ammonia solution -> A blue precipitate forms
Iron (II) -> Add dilute sodium hydroxide or ammonia solution -> A pale green precipitate forms
Iron (II) -> Add dilute sodium hydroxide or ammonia solution -> A red - brown precipitate forms
Zinc -> Add dilute sodium hydroxide or ammonia solution -> A white precipitate forms

Describe and use the following tests to identify: aqueous cations: ammonium, calcium, copper(II), iron(II), iron(III) and zinc, by means of aqueous sodium hydroxide and aqueous ammonia as appropriate (formulae of complex ions are not required). cations: flame tests to identify lithium, sodium, potassium and copper(II) anions: carbonate (by reaction with dilute acid and then limewater), chloride (by reaction under acidic conditions with aqueous silver nitrate), nitrate (by reduction with aluminium) and sulfate (by reaction under acidic conditions with aqueous barium ions) gases: ammonia (using damp red litmus paper), carbon dioxide (using limewater), chlorine (using damp litmus paper), hydrogen (using a lighted splint), oxygen (using a glowing splint)