K.C.S.E Chemistry Q & A-MODEL 2017.PP2.Q N.2

23/11/2020

KCSE Chemistry 2017 Topical Questions and Answers

All Questions Featuring Chemistry Form 1, Form 2, Form 3, Form 4, Paper 1, Paper 2 and Paper 3

The conductivity of some substances was investigated. The observations made were recorded in
Table 1. Use it to answer the questions that follow.

(a) (i) Identify a substance that is a metal. Give a reason.
(ii) Substance F does not conduct electricity in solid state but conducts in molten or aqueous state.
Explain.
(b) Copper(II) sulphate solution was electrolysed using the set up in Figure 1.

(i) State the observations made during electrolysis.
(ii) Write the equation for the reaction that occurs at the anode.
(iii) State the expected change in pH of the electrolyte after electrolysis.
(c) The experiment was repeated using copper electrodes instead of carbon electrodes.
Describe the observations made at each electrode.
(d) Electroplating is an important industrial process.
What is meant by electroplating.
(iii) During electroplating of an iron spoon, a current of 0.6 amperes was passed through aqueous silver nitrate solution for 1 1/2 hours. Calculate the mass of silver that was deposited on the spoon.
(Ag = 108.0 ; I F = 96,500 C /mol)

ANSWERS

(a)(i) G — Contains delocalized electrons present in solid and molten state.
(ii) In solid state, the ions are rigidly held in position and cannot move, hence will not conduct.
In molten/aqueous state, the ions are mobile and will be able to conduct electric current.
(b)(i)The blue electrolyte fades and finally changes from blue to colourless,
Effervescence / bubbles of a colourless gas.
A brown deposit forms on the cathode.

(c) With copper electrodes:
Anode will go into solution as copper ions hence it decreases in mass/size.
Brown deposit forms at the cathode hence the cathode increases in mass.
(d) (i) This is the coating of an article / object with another metal by electrolytic method /electrolysis.