(a)(i) List two elements which react with steam at red heat to produce hydrogen.
(ii) Explain why an aqueous solution of potassium bromide turned reddish brown on bubbling chlorine through it.
(iii) Write an equation for the reaction in (a)(ii).
(b)(i) Name two types of chemical industry that use limestone as raw material.
(ii) Give one example of hygroscopic substances.
(iii) Copy and complete the table below.
|
Salt to be prepared |
Starting material |
Method of preparation |
| PbSO\(4\) | Pb(NO\(_3)_{2(ag)}\) | – |
| KNO\(_3\) | KOH | Neutralization |
| CaCl\(_2\) | CaCO\(_3\) | – |
| FeCl\(_3\) | Fe\(_(s)}\) | – |
| CuSO\(_4\) | CuO | – |
(c) In the contact process for the manufacture of tetraoxosulphate (VI) acid;
(i) State how sulphur (IV) oxide is obtained;
(ii) Write an equation for the reaction that takes place in the catalyst chamber;
(iii) Give the steps required to convert sulphur (VI) oxide to acid.
(d)(i) List two disadvantages of hard water.
(ii) Mention three methods which can be used to remove both permanent and temporary hardness in water at the same time.
(iii) State the role of alum and chlorine respectively in the purification of water for town supply.
Explanation
(a)(i) Two elements which react with steam to produce hydrogen are Fe, Zn, Al, Mg (any two).
(ii) An aqueous solution of KBr turned reddish brown on bubbling chlorine through it because the chlorine oxidized the KBr / displaced the bromine from KBr. The free bromine coloured the solution.
(iii) Equation for the reaction involved in (a)(ii) Cl\(_2\) + 2KBr --> 2KCI + Br\(_2\)
(b)(i) Types of chemical industries that use limestone as raw materials: Iron/steel/iron and steel/metallurgical industry, paper industry, cement industry, glass industry, fertilizer industry.
(ii) Examples or hygroscopic substances CuO\(_2\) Conc. H\(_2\)SO\(_4\) . CaO alumina, silica gel (any one)
|
Salt to be prepared |
Starting material |
Method of preparation |
|
PbSO\(_4\) KMO\(_3\) CaCl\(_3\ FeCl\(_3\) CaSO\(_4\)
|
Pb(NO_3\) KOH Fe\(_{(s)}\) CaCO\(_3\) CuO
|
Double decomposition/precipitation Neutralisation Action of acid HCl Direct combination or action of HCl followed by oxidation Neutralisation
|
(c)(i) The SO\(_2\) is obtained by burning sulphur in air or roasting sulphide ore in air: S + O\(_2\) -> SO
(ii) The equation for the reaction in the catalyst chamber is 2SO\(_2\) + O\(_2\) --> 2SO\(_3\).
(iii) The steps required to core SO\(_3\) to acid arc:
- Dissolution in conc. H\(_2\)SO\(_4\) to form oleum. Or 2SO\(_3\) + H\(_2\)SO\(_4\) --> H\(_2\)S\(_2\)O\(_7\).
- Dilution of oleum with calculated amount of of water. Or H\(_2\)S\(_2\)O\(_7\) + H\(_2\)O --> 2H\(_2\)SO\(_4\)
(d)(i) Wastes soap, causes furl in pans and kettles / scales in boilers, results in burst pipes/narrow tubes in boilers, reduces heat capacity of boilers, makes dirty marks on clothes during washing or dying (any two).
(ii) Methods that remove both temporary and permanent hardness in water simultaneously.
- Addition of washing soda ((Na\(_2\)CO\(_3\)).
- Distillation.
- Use of cation exchange resins / permutit / zeolite
(iii) Role of alum in purification of water is coagulation. Role of chlorine in purification of water is killing of bacteria, germicide / sterilization