Questions on Ionic Equations, Colours of Cations & Anions, Acid, Bases, Alkalis, Salts

Q1. Zinc Nitrate reacts with Aqueous Ammonia (NH4OH) to form a salt and a base.
       (i) Name the salt and base.
       (ii) Describe the observation for the reaction.
       (iii) Write a chemical equation for the reaction (include state symbols).
       (iv) Write an ionic equation for the reaction.

Ans: (i) The salt is ammonium nitrate (NH4NO3) and the base is zinc hydroxide ( Zn(OH)2 )
        (ii) A white precipitation is form. The white precipitate is soluble in excess to give a colourless solution.
        (iii)  Zn(NO3)2 (aq) + 2 NH4OH (aq) = Zn(OH)2 (S) + 2 NH4NO3 (aq)
           (iv) Zn²⁺ (aq) + 2 OH^- (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.

Ans: (i) (NH4)2SO4 (S) + 2 NaOH (aq) = Na2SO4 (S) + 2 NH3 (G) + 2 H2O (L)
        (ii) 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 aluminum 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 anion. Name this anion.
       (iii) Give a possible cation which gives the green solution.

Ans: (i) The gas evolved is ammonia (NH3).
        (ii) The anion is nitrate (NO3^-).
        (iii) The possible cation is 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.
       (ii) Write an ionic equation for the reaction.

Ans: (i) Because potassium sulfate is soluble salt, so it cannot be prepared by precipitation method. Titration method is for group (I) and ammonium salt only and potassium sulfate is also a group (I) salt, hence it can be prepared using titration method.
        (ii) 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.
       (ii) Why excess zinc carbonate is used?
       (iii) Briefly explains how the zinc chloride crystals can be obtained.

Ans: (i) ZnCO3 (S) + 2 H⁺ (aq) = Zn²⁺ (aq)  + CO2 (G) + H2O (L)
                (ii) Because the excess zinc carbonate is used to react with hydrochloric acid to prepare the zinc chloride salt as zinc chloride salt is soluble but not group(I) or ammonium salt. The zinc carbonate is used to excess tp make sure that is has completely reacted with hydrochloric acid to form calcium chloride.
        (iii) Firstly, add the excess zinc carbonate solid to a beaker of dilute hydrochloric acid until there is excess zinc carbonate left behind.
              Secondly, filter to remove the excess unreacted zinc carbonate solid.
              Thirdly, evaporate the zinc chloride solution to remove the water and make a saturated salt solution.
              Lastly, leave the hot saturated solution to cool down and it will form zinc chloride crystals.