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07:29 / Wednesday 28 September 2011
Q1. Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.
i) Name the salt and the base.
ii) Describe the observations for the reaction.
iii) Write a chemical equation for the reaction (include state symbols).
iv) Write an ionic equation for the reaction.
i) The salt formed is Ammonium Nitrate (NH4NO3) and the base is Zinc Hydroxide .
ii) White ppt. is formed.
iii) Zn(NO3)2 (aq) + 2NH4OH (aq) = Zn(OH)2 (s) + 2NH4NO3 (aq)
iv) 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.
ii) Describe a test for the gas.
i) (NH4)2SO4 (aq) + 2NAOH (aq) --> 2NH3 (g) + 2H2O (l) + Na2SO4 (aq)
ii) Use red litmus paper and put it over the ammonia gas , it will turn the red litmus paper to blue litmus paper.
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.
ii) This is a confirmatory test for an anion. Name this anion.
iii) Give a possible cation which gives the green solution.
i) Ammonia gas
ii) Nitrate ion
iii) Iron (II) ionQ4. 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.
ii)Write an ionic equation for the reaction.
i) Because sulfuric acid, potassium hydroxide and potassium sulphate salt are soluble, therefore we use this method
ii)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.
ii) Why excess zinc carbonate is used?
iii)Briefly explain how the zinc chloride crystals can be obtained.
i) ZnCO3 (s) +2H+ (aq) --> H2O (l) +CO2 (g) + Zn2+
ii) Excess zinc carbonate is used to ensure that all the hydrochloric acid is completely reacted.When there are excess white zinc carbonate seen,the reaction has stopped.
iii) Add excess zinc carbonate to hydrochloric acid then filter out all the excess zinc carbonate. Boil the solution in evaporating dish then control the fire to prevent the salts from escaping out. Lastly, let the solution cool down then zinc chloride crystal is formed.
Sodium is a metal because ..........................
