Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.
(i) Name the salt and the base.
Salt:zinc nitrate
Base: zinc hydroxide.
(ii) Describe the observations for the reaction.
white precipitation is formed, soluble in excess giving a colourless solution.
(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.
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) --> 2NH3 (g) + Na2SO4 (aq) + 2H2O (L)
(ii) Describe a test for the gas.
It 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 (NO3-) in solution
(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.
Potassium hydroxide and sulfuric acid and potassium sulfate salt are all soluble and colourless solutions so titration is the best method.
(ii) Write an ionic equation for the reaction.
H+ (aq) + OH- (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.
(CO3) 2- (aq) + 2H+ (aq) --> H2O (L) + CO2 (g)
(ii) Why excess zinc carbonate is used?
Excess is used to ensure that it has completelty reacted with the hydrocloric acid.
(iii) Briefly explain how the zinc chloride crystals can be obtained.
Add excess zinc carbonate to a beaker of hydrochloric acid until there is excess zinc chloride left behind. Filter to remove the excess unreacted zinc carbonate solid. Then evaporate the zinc chloridesolution to remove the water and make a saturated solution. The hot saturated solution would form zinc chloride crystals when cooled.
