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Monday 26 September 2011


Q1. Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.

i) Name the salt and the base.
Ammonium Nitrate (NH4NO3). The base is Zinc Hydroxide .
ii) Describe the observations for the reaction.
White ppt. 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.
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) + 2H2O (l) + Na2SO4 (aq)
ii) Describe a test for the gas.
Use red litmus paper by holding it over the ammonia gas. The red litmus paper will turn 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 gas
ii) This is a confirmatory test for an anion. Name this anion.
Nitrate ion
iii) Give a possible cation which gives the green solution.
Iron (II) ion
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.
It is because sulfuric acid, potassium hydroxide and potassium sulphate salt are soluble.
ii)Write an ionic equation for the reaction.
2H+ (aq) + 2OH- (aq) -> H2O
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) -> H2O (l) +CO2 (g) + Zn2+

ii) Why excess zinc carbonate is used?
It is to ensure that all the hydrochloric acid is completely reacted to form the chloride salt.
iii)Briefly explain how the zinc chloride crystals can be obtained.
Add excess zinc carbonate to hydrochloric acid. Filter out all the excess zinc carbonate after that. Boil the solution in a evaporating dish. Control the fire to prevent the salts from “jumping” out. Heat until there is little fluid left. Let the solution cool under the fan. Zinc chloride crystal is formed after it dries.

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