(a) A solution of CuSO\(_4\) was electrolyzed between pure copper electrodes and the following results were obtained:
Mass of copper anode before experiment = 7.20 g
Mass of copper anode after experiment = 4.00 g
Mass of copper cathode before experiment = 5.75 g
From the information provided,
(i) calculate the mass of the cathode, after the experiment.
(ii) write an equation for the reaction at the I. anode, II. cathode.
(iii) state whether the colour of the solution would change during the electrolysis. Give a reason for your answer.
(iv) if the electrolysis was carried out for 1 hour 20 minutes with a current of 2.0 amperes, determine the value of the Faraday.
(b) Consider the reaction represented by the following equation:
MnO\(^-_4\) + I\(^-\) + H\(^+\) \(\to\) I\(_2\) + H\(_2\)O + Mn\(^{2+}\)
Write balanced half equation for the (i) oxidation reaction, (ii) reduction reaction.
(c)(i) Describe briefly how tin can be extracted from its ore.
(ii) State one use of tin.
(iii) Mention one property that makes tin suitable for the use stated in (c)(ii)
(d)(i) What is meant by the term pollution?
(ii) Explain why it is dangerous to run a generator in a closed room.
Explanation
(a)(i) Loss of mass in anode = 7.20 – 4 = 3.20g
Mass of cathode after the experiment = 5.75 + 3.20
= 8,95g.
(ii) I. Anode : Cu \(\to\) Cu\(^{2+}\) + 2e\(^-\)
II. Cathode : Cu\(^{2+}\) + 2e\(^-\) \(\to\) Cu
(iii) Colour of solution does not change because copper ions discharged at the cathode are replaced by copper ion (Cu\(^{2+}\)) produced at the anode.
(iv) 1 mole Cu = 2F mole of Cu deposited = \(\frac{3.2}{63.5}\) = 0.05
number of Faradays used = 0.05 x 2 = 0.1F
Quantity of electricity used = 80 x 60 x 2 = 9600C
9600 = 0.1F
F = \(\frac{9600}{0.1}\) = 96000C
(b) MnO\(^-_4\) + 1\(^-\) + H\(^+\) \(\to\) I\(_2\) + H\(_2\)O + Mn\(^{(2+)}\)
(i) 2\(^-\) - 2e \(\to\) I\(_2\) (oxidation).
(ii) MnO\(^-_4\) + 8H\(^+\) + 5e\(^-\) \(\to\) Mn\(^{(2+)}\) + 4H\(_2\)O (reduction)
(c)(i) Tin ore (SnO\(_2\)) or casseterite is crushed and washed with water. It is roasted in air, the product is mixed with powdered charcoal and heated strongly at about 1300°C to obtain molten tin.
(ii) Uses of tin: (1) It is used for making alloys (2) It is used for coating steel or for tin plating (electroplating).
(iii) Corresponding property: (1) It has high tensile strength, lightness (2) It is non-toxic, non-corrosive, inert and unreactive.
(d)(i) Pollution is the contamination of the environment by substances in concentrations that can cause injur, to lives and property.
(ii) It is dangerous to run a generator in a room because the carbon (II) oxide released from the exhaust combines with blood, leading to blood poisoning which can result to death.