(a)(i) State two industrial uses of hdrogen.
(ii) Consider the equation below. Mg(HCO\(_3\))\(_{2(aq)}\) \(\to\) MgCO\(_{3(g)}\) + H\(_2\)0\(_{(l)}\) + CO\(_{2(g)}\)
1. State the type of hardness of water being removed as shown by the above equation.
2. Give two disadvantages of hardness of water.
(b)(i) In the extraction of aluminium by electrolysis, graphite electrodes are used. State the disadvantages of using this type of electrode.
(ii) Calcuim oxide reacts with water to form slaked line: I. Write a balanced equation for this reaction; II. State one use of slaked line.
(c)(i) What is meant by saponification?
(ii) List the raw materials needed for the manufacture of soap.
(iii) Name the main by-product obtained from the manufacture of soap.
(d) With the aid of chemical equations explain briefly how iron is extracted in the blast furnace using iron ore, coke and limestone as raw materials at the:
(i) bottom of the furnace; (ii) middle of the furnace (iii) top of the furnace.
Explanation
(a)(i) Two industrial uses of hydrogen: —filling of weather balloons. —manufacture of plastics. —manufacture of ammonia by the Haber process. —manufacture of methanol. —oil refinery process/hydrocracking —used in fuel cells. —manufacture of margarine. —in oxy-hydrogen flame (for welding and cutting metals). —as reducing agent in production of metals, e.g. Cu and.Pb from their oxides. —conversion of coal to crude oil. —(liquid) hydrogen is used as rocket fuel/gaseous fuel (Any 2).
(ii) Mg(HCO\(_3\))\(_{2(aq)}\) —> MgCO\(_3\)\(_{(s)}\) + H\(_2\)O\(_{(l)}\) + Cu\(_3\).
In the equation above: (1) the type of hardness of water being removed is temporary hardness of water. (2) two disadvantges of hardness of water are: —scales/furrinab of kettles/pipes causing blockage leading to power wastage. —soap is wasted not suitable for laundry. —not suitable for use in tanning, textiles and paper production (Any 2).
(b)(i) Disadvatnages of using graphite electrodes in the extraction of aluminium by electrolysis: At high temperature oxygen gas produced at the anode reacts with the graphite electrodes to form carbon(IV) oxide.
(ii) Balanced equation of reaction between calcium oxide and water to form slaked lime: CaO + H\(_2\)O \(\to\) Ca(OH)\(_2\)
(iii) One use of slaked lime: —used to treat acidic soil. —used to make mortar/plasters/cement/hold bricks. —in manufacture of glass. —purification of water/removing hardness of water. —manufacture of white wash. —to test for CO\(_2\). —production of bleaching powder: —to recover or produce ammonia from ammonium chloride used in solvay process.
(c)(i) Saponification is the alkaline hydrolysis of fats/oils to produce soap and propane —1,2,3-triol
(ii) Raw materials needed for the manufacture of soap: —oil/fat. —alkali (1) (sodium hydroxide/potassium hydroxide
(iii) Main by-product obtained from the manufacture of soap is propane —1,2,3-triol.
(d) Extraction of iron in the blast furnace using iron-ore, coke and limestone as raw materials with the aid of chemical equations..
(i) Bottom of furnace: The O\(_2\) in the hot air combines with carbon(coke) to produce carbon (IV) oxide which is reduced to carbon (II) oxide.
C + O\(_2\) \(\to\) CO\(_{2(g)}\)
CO\(_{2(g)}\) + C \(\to\) 2CO\(_{(g)}\)
(ii) Middle of the furnace: The calcium carbonate CaCO\(_3\) decomposes under great heat to form CO\(_2\) and CaO and CaCO\(_3\) decomposes to remove the impurities SiO\(_2\)
CaCO\(_3\) —> CaO\(_s\) + CO\(_{2(g)}\)
CaO + SiO\(_2\) --> CaSiO\(_3\).
(iii) Top of furnace: Iron (III) oxide is reduced to metallic iron Fe\(_2\)O\(_2\) + 3CO 2Fe + 3CO\(_2\)
OR Fe\(_3\)O\(_4\) + 4CO —> 3Fe + 4CO\(_2\).