Monday, September 19, 2011

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 (NH₄NO₃) and the base is Zinc Hydroxide .

ii) Describe the observations for the reaction.

Ans: White ppt. is formed.

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

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

iv) Write an ionic equation for the reaction.

Ans: : 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.

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

ii) Describe a test for the gas.

Ans: Use a moist red litmus paper and hang it over the ammonia gas , it will turn the red litmus paper to 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: Ammonia gas

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

Ans: Nitrate ion

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

Ans: 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.

Ans: As sulfuric acid, potassium hydroxide and potassium sulphate salt are soluble. Hence, this method is recommended for the preparation of the salt.

ii)Write an ionic equation for the reaction.

Ans: 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.

Ans: ZnCO₃ (s) +2H⁺ (aq) --> H₂O (l) +CO₂ (g) + Zn²⁺

ii) Why excess zinc carbonate is used?

Ans: 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.

Ans: Add excess zinc carbonate to hydrochloric acid then filter out all the excess zinc carbonate. Boil the solution in a evaporating dish, control the fire to prevent the salts from “popping” out. Finally, let the solution cool under the fan and zinc chloride crystal is formed.