(a)(i) Outline the steps involved in the purification of water for town supply.
(ii) Give two cations that can cause hardness in water.
(iii) State two disadvantages of hardness of water.
(iv) List two sources of water pollution.
(b)(i) Explain briefly why water is a good solvent for sodium chloride but not for oil.
(ii) State the function of H\(_2\)SO\(_4\) in each of the following reaction equations:
(i) C\(_2\)H\(_5\)OH\(_{(l)}\) \(\to\) C\(_2\)H\(_{4(g)}\)
(ii) MgO\(_{(s)}\) + H\(_2\)SO\(_4\)\(_{(aq)}\) —> MgSO\(_{4(aq)}\) + H\(_2\)O\(_{(l)}\)
(iii) C\(_{(s)}\) + conc. H\(_2\)SO\(_4\) –> CO\(_{(g)}\) + SO\(_{2(g)}\) + H\(_2\)O\(_{(l)}\)
(c) (i) Give the two products formed when chlorine water is exposed to sunlight.
(ii) I. Which of the compounds is suitable for the preparation of standard alkaline solution?
II. Give a reason for your answer in (c)(ii)I
Explanation
(i) (1) Aeration/exposure to sunlight.
(2) Add alum/coagulation /flocculation.
(3) Sedimentation.
(4) Fi!teration.
(5) Add chlorine /disinfectant.
(6) Add flouride/iodide.
(7) Add Ca(OH)\(_2\) / pH control.
(ii) Cations that can cause hardness in water: Mg, Ca, Fe.
(iii)Disadvantages of Hardness of Water:
(1) It wastes soap.
(2) Forms stain on white clothing and material
(3) Forms boiler scale and kettle fur / damage.
(4) It is unsuitable for industrial processes, e.g. dyeing and tanning.
(iv) Sources of Water Pollution:
(1) Wastes from industries, e.g. brewery.
(2) Agricultural activities, e.g. fertilizer.
(3) Waste from quarry activities.
(4) Refuse from plant and animal origin.
(5) Sewage (industrial and domestic).
(6) Oil spillage.
(b)(i) Water is a polar solvent and can therefore easily dissolve sodium chloride which is ionic / polar salt. Oil, on the other hand, is non-polar and, hence cannot dissolve in water which is polar.
(ii) - H\(_2\)SO\(_4\) - As a dehydrating agent.
- H\(_2\)SO\(_2\) - As an acid.
- H\(_2\)SO\(_4\) As an oxidizing agent.
(c)(i) HCl and O\(_2\)
(ii)(I) Na\(_2\)CO\(_3\)
(II) Na\(_2\)CO\(_3\) is stable in air and can be weighed accurately. NaOH absorbs water / deliquescent and cannot be weighed accurately.