Chemistry Paper 2 Marking Scheme
KCSE CLUSTER TESTS 27
Chemistry Paper 2
1(a) E (1mrk)
Its ions have the greatest tendency to accept electrons // Has the highest positive electrode potential // Ions
are strongest oxidizing agent
(ii) NB: The arrow should be on the wire or electrode but not outside the diagram.
(iii).To complete the circuit // maintain change balance // replace ions used up in half cells. (1mrk)
C (i) OH- ions migrate to the anode(1mrk). OH- ions are preferentially discharged to form O2 gas. // OH- ions oxidized to form O2 (g)(1mrk)
(ii) Copper anode dissolves to give Cu2+(aq) // Copper anode is oxidized (1mrk) this is because oxidation of copper requires lesser energy than oxidation of OH-
13 marks
(a) (i) Dehydration (1mrk)
(ii) Warm // Heat½ // presence of Conc.H2SO4½
(iii) Chloro-ethene
(iv) Ethanol / CH3CH2OH(l)
(b) (i) C2H4O2 ½ it has a melting point of 289.6K which is higher than 283.0K½
(ii) C3H8O is more soluble in water than C5H12.This is because C3H8O hydrogen bonds which improves it solubility while C5H12 does not hydrogen bond
13 marks
.(a)(i) On the grid [ period 3 and group 4]
(ii) L (1mrk). Atomic radius decreases across a period from left to right // The nuclear charge or no. of protons increase across the period hence electrons are strongly attracted towards nuclear
b) Q is more reactive with sodium than R.(1mrk) This is because. Q has a higher tendency to accept electrons
than R// Q is more electronegative than R
d). In bulbs to provide an inert atmosphere so as to minimize the rate of oxidation of filament. (mrk
11 marks
(ii) The amount of heat given out when one mole of a substance is completely burnt in excess oxygen at standard conditions
(iii)Heating value is – 40.32 kilo joules.// the heat given out when 1g of butane is burnt.
11 marks
a)(i) To remove the metal oxide layer which interfere with reaction
b).(i) Graph:
-Labeling and axis (correct) – (1mrk)
- Plotting [all points correct] – (1mrk)
- Smooth Curve – (1mrk)
12 marks
ii) – In treatment of drinking water
-Manufacture of chloroform aneasthetic
-Manufacture of germicide, fungicides and pestcides
11 marks