MARKING SCHEME PAPER 2
i) Molten sulphur 1
ii) To melt the sulphur and maintain it in molten state up to the surface 1/ to force hot
sulphur from underground
iii) - has low density 1
- Insoluble in water / immiscible in water 1
- has low M.P / M.P lower than 170oC any two = 2mks
b) i) contain many gases 1
The gases can be separated by physical means 1
ii) To dry / remove moisture from SO2 and air 1
iii) - platinum / platinised asbestos 1
- Vanadium (V) oxide / pentoxide 1
- Titanium any two = 2mks
iv) - to maintain / regulate the optimum temp. of about 450oC 1
- provide reactants with enough energy to react 1
- prevent decomposition of products
- conserve heat / recycle heat / reduce cost of production any 2 = 2mks
v) To unknown solution add BaCl 2 or Ba(NO3)2 presence of white ppt of BaSO 3. Add dil HCL or
HNO3. The white ppt dissolves with evolution of a colourless gas So 3 evidenced by effervescence//
using acidified KMno7 and K2Cro7 from purple to colourless orange to green 2mk
vi) Colour changes from blue to white 1 Conc. H 2SO4 is a strong dehydrating agent ½ hence
removes elements ½ of water (H2 and O2) in hydrated copper II sulphate
2.i ) J, ½ its E is 0.00V ½
ii) G2+(aq) + 2e G(s) and ½L2(g) + e– L–(aq)
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iii)
Salt bridge 1
Workability 1
-Electrodes dipped in own electrolyte (only)
Voltimeter// Ammeter 1
iv) E.m.f E = Ereduced - Eoxidised
= +0.34 - -2.90V 1
= +3.24V 1
Or
G(s) G2+(aq) + 2e– E = +2.90V ½
K2+(aq) + 2e– K(s) E = +0.34V ½
G(s) + K2+(aq) G2+(aq) + K(s) E = 3.24V 1
v) Both will react since the E value will be positive 1
E = +0.34 - (-2.38)V ½ = +2.72V ½
b) i) Cu2+(aq) + 2e– Cu(s)
ii) Q = It
= 0.4 x 5 x 3600 ½
= 7200C ½
96500 x 2C =63.5g
7200C
Mass dissolved
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7200 x 63.5g 1
193000
= 2.369g ½
3.a)i) Sweet smelling
ii) sodium / magnesium / calcium
- Metals above hydrogen in the reactivity series.
iii) Add sodium carbonate / hydrogen carbonate C3H7COOH will effervescence but C4H9OH does
not //
- Use universal indicator to determine pH. C3H7COOH has a pH {4, 5, 6} while C4H9OH has a
pH of 7 //
- Ignite the substances
C3H7COOH does not burn while C4H9OH burns with a blue flame //
- Use blue litmus papers, turns red in C3H7COOH while it remain blue in C4H9OH
C 4 H 9 OH +6 O 2 →4 CO 2 +5 H 2 O
iv)
v) Step II - Esterification
Step VII - oxidation
vi) RFM = (4 × 12) + 9 + 16 + 1 = 74 ½
Moles = 7.4 = 0.1 moles
74
M.R ½ 1 : 4
Moles of CO2 = (0.1 × 4) ½ = 0.4 moles
Volume = (0.4 × 22.4) ½ = 8.96 l ½
OR
74g ½ yields (4 × 22.4) l =7.4g = 8.96 l ½
viii) - Add it to white anhydrous copper (II) sulphate which turns to blue hydrated copper (II)
sulphate//
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-Add it to blue cobalt (II) chloride (paper) which turns to pink 2
4. i) Aluminium metal is reactive.
ii) X Anode Y is cathode.
iii) i) Iron (iii) oxide, silicon (IV) oxide or titanium oxide accept any two correct.
ii) Adding cryolite (Na3AlF6) which lowers the melting point of alumina
2 O(2−
l ) → 2 O 2( g) + 4 e
iv)
Penalise accordingly.
v) Anode, since oxygen produced at that electrode react with carbon hence used to be replaced.
vi) Stronger/ harder OR
Higher tensile strength
5. a) i) I ; most electronegative 1 // has highest electron affinity.
ii) Halogens 1
+ 2-
2 C H
iv) F is bigger // has a bigger atomic radius than I. 1
I has stronger nuclear attraction than F, hence its electrons are strongly attracted to the
nucleus.
b) i) Its ions in the solid state are held in fixed position and are not mobile .
In liquid state the ions become mobile, hence conduct an electric current.
ii) Giants atomic structure. ½. High ½ melting and boiling points but does ü½ not conduct in
molten /solid state.
Q its M.P is lower than room temp but its B.P is higher than room temp.
6. i)Due to production of CO2 which escape to the atmosphere 1
ii) CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) 1
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iii) Grind marble chips to powder form 1
Increase concentration of HCl 1
Increase the temperature of the reactants any 2 correct = 2mks
iv) The reaction is complete since calcium carbonate has been used up 1
v) White precipitate ½ insoluble ½ in excess ammonia solution
vi)- global warming
- cause acid rain any one = 1mk
C a ta lysed
vii)
E ne rgy
P rog re ss o f re actio n
viii) i) Favours forward reaction1orange colour intensify concentration of hydrogen ions increases
ii) Favour backward reaction 1 yellow colour formed the reaction produces heat/ exothermic
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