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

i) Name the salt and the base.

Ans: The salt is ammonium nitrate and the base is zinc hydroxide.

ii) Describe the observations for the reaction.

Ans: When zinc nitrate reacts with aqueous ammonia, white precipitation is form. The white precipitate is soluble in excess to give a colourless solution.

iii) Write a chemical equation for the reaction (include state symbols).

Ans: Zn(NO3)2 (aq) + 2NH4OH (aq) à Zn(OH)2 (s) + 2NH4NO3 (aq)

iv) Write an ionic equation for the reaction.

Ans: : Zn2+ (aq) + 2OH- (aq) àZn(OH)2 (s)

Q2. Ammonium sulfate is heated with sodium hydroxide.

i) Write a chemical equation (include state symbols) for the reaction.

Ans: 2(NH4)2SO4 (aq) + 2NAOH (aq) à 2NH3 (g) + 2H2O (l) + Na2SO4 (aq)

ii) Describe a test for the gas.

Ans: The gas formed is ammonia. Hold a piece of dump red litmus paper over the mouth of the test tube. The ammonia gas will turn the 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.

Ans: The gas evolved is ammonia gas.

ii) This is a confirmatory test for an anion. Name this anion.

Ans: The anion is nitrate (NO3-).

iii) Give a possible cation which gives the green solution.

Ans: One possible cation will be Iron (II), Fe2+.

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.

Ans: Potassium sulfate is a group (I) and soluble salt. Titration method is for group (I) and ammonium salt. Therefore, the salt can be prepared using titration method.

ii)Write an ionic equation for the reaction.

Ans: 2H+ (aq) + OH- (aq) à 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.

Ans: CO32+ (aq) +2H+ (aq) à H2O (l) +CO2 (g)

ii) Why excess zinc carbonate is used?

Ans: To ensure that all the hydrochloric acid is completely reacted.

iii) Briefly explain how the zinc chloride crystals can be obtained.

Ans: Step 1: Add the excess zinc carbonate solid to a beaker of dilute hydrochloric acid until there is excess zinc carbonate.

 Step 2: Filter to remove the excess unreacted zinc carbonate solid.

 Step 3: Evaporate the zinc chloride solution to remove the water and to obtain a saturated salt solution.

  Step 4: Leave the hot saturated solution to cool down and to form zinc chloride crystals.