a)(i) Give two uses of ammonia.
(ii) Name the process by which ammoniacal liquor can be obtained from coal and list two other products of the reaction
(iii) What type of reaction is involved in the conversion of ammoniacal liquor to (NH\(_4\))\(_2\)SO\(_4\) by dilute H\(_2\)SO\(_4\)?
(iv) Sketch and label an energy profile diagram to show the effect of presence of Pt/Rh on the reaction represented by the following equation: 4NH\(_3\) + 5O\(_2\) \(\to\) 6H\(_2\)O + 4NO; \(\Delta\)H = —907 kJmol\(^1\)
(b) Rock salt is an impure form of sodium chloride.
(i) Outline a suitable procedure for preparing a pure sample of sodium chloride from rock salt.
(ii) State two methods that can be used to prepare chlorine from rock salt. Write an appropriate equation in each case.
(c) Lead pigments were used in a water colour painting which turned black after prolonged exposure to an air pollutant. The original colour was restored by using H\(_2\)O\(_2\) which converted the black substance to a simple, white lead (II) salt.
(i) Which pollutant turned the painting black?
(ii) Write the formula of the black substance
(iii) What is the white salt?
(iv) State the role of H\(_2\)O in the restoration process.
Explanation
(a)(i) -As a softening agent in temporary hard water.
-As a solvent for removing grease and oil stains.
-Cooling agent in some refrigerators.
-It is used in the manufacturing of HNO\(_3\) and Na\(_2\)CO\(_3\)
- In the manufacture of fertilizers.
(ii) By destructive distillation of coal and wood, the ammoniacal liquor is obtained by fractional distillation. Other products of the reactions are coal tar, coal, gas and coke.
(iii) Displacement reaction.
(iv)
The rocKsalt is an impure form of NaCI.
(b)(i) It can be mined as a solid or pumped out of the ground as brine. The best method of obtaining NaCI from the brine is by industrial electrolysis
(ii) By electrolysis and displacement reaction. At the anode; CI --> CI + e\(^-\)
CI + CI --> + Cl\(_2\) ; 2NaCl + MnO + 2H\(_2\)SO\(_4\) -> Na\(_2\)SO\(_4\) + MnSO\(_4\) + 2H\(_2\)O + Cl\(_{2}\)
(c)(i) -SO\(_2\)
(ii) -PbS
(iii) -PbCl\(_2\)
(iv) Bleaching agent.