Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.
(i) Name the salt and the base.
The salt is Zinc hydroxide, Zn(OH)2. The base is ammonium nitrate, NH4NO3.
(ii) Describe the observations for the reaction.
White precipitate is formed.
(iii) Write a chemical equation for the reaction (include state symbols).
Zn(NO3)2(aq) + 2NH4OH(aq) - Zn(OH)2(s) + 2NH4NO3(aq)
(iv) Write an ionic equation for the reaction. (aq)
Zn2+(aq) + 2OH-(aq) - Zn(OH)2(s)
Q2 Ammonium sulfate is heated with sodium hydroxide.
(i) Write a chemical equation (include state symbols) for the reaction.
(NH4)2SO4(aq) + 2NaOH(aq) - Na2SO4(s) + 2H2O(l) + 2NH3(g)
(ii) Describe a test for the gas.
Turns damp red litmus paper blue.
Q3 An unknown green solution is heated with a piece of aluminium foil and sodium hydroxide solution.
(i) The gas produced turns damp red litmus paper blue. Name the gas evolved.
Ammonia.
(ii) This is a confirmatory test for an anion. Name this anion.
Nitrate.
(iii) Give a possible cation which gives the green solution.
Iron(III).
Q4 Sulfuric acid is titrated with potassium hydroxide in the preparation of potassium sulfate salt.
(i) Explain why this method is recommended for the preparation for this salt.
The salt is soluble and is in group I hence titration is used to carry out this experiment.
(ii) Write an ionic equation for the reaction.
OH- (aq) + H+ (aq) - H2O (l)
Q5 Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt.
(i) Write an ionic equation for the reaction.
ZnCO3 (s) + 2H+ (aq) - Zn2+ (aq) + H2O (l) + CO2 (g)
(ii) Why excess zinc carbonate is used?
To ensure that the hydrochloric acid is completely neutralised.
(iii) Briefly explain how the zinc chloride crystals can be obtained.
Zinc carbonate reacts with hydrochloric acid to form salt and excess zinc carbonate is lefted behind. Filter to remove excess zinc carbonate and heat the filtrate to remove the water and make a saturated solution. The hot saturated solution forms zinc chloride crystals when cool.
