2015 SPECIMEN MOCK EXAMINATION CHEMISTRY PAPER 2 MARKING SCHEME

2015 SPECIMEN MOCK EXAMINATION CHEMISTRY PAPER 2 MARKING SCHEME

1. a) i) - Manganese (IV) 1 oxide (penalize if formula)

- Hydrogen peroxide 1 (penalize for formula)

b)

2H2O2(l)

MnO2 2H2O(l) + O2(g)

B.B + S.S ? award fuly

B.B ? S.S ? penalize ? mk

S.S ? B.B ? penalize fully

c) i) - To ensure that all oxygen has been used. 1

ii) - For maximum contact between copper and oxygen so that the reaction occurs 1

iii) - Brown copper turnings charged their colour to a black solid 1

iv) 2Cu(s) + O2(g) B.B + S.S ? award fuly

2CuO(s)

B.B ? S.S ? penalize ? mk

S.S ? B.B ? penalize fully v) 120cm3 ? 95.5cm3 = 24.5cm3 1

24.5 x 100 ?

120

= 20.42% ?

vii) Used by patients with respiratory problems

d)

2NaNO3(s) heat 2NaNO2(s) + O2(g) ?

RFM = 46 + 28 + 96 = 170 => 22.4dm ?

8.5g

?

8.5 x 22.4 = 1.12dm3 1

170

2. a) i) Ammonia ?

ii) Carbon (IV) oxide ?

iii) Carbon / coke / Graphite / Diamond ?

iv) Calcium oxide ?

v) Ammonium chloride ?

vi) Sodium hydrogen carbonate ?

(penalize for formula)

b) i) Chamber I

CaO(s) + H2O(l) B.B + S.S ? award fuly

Ca(OH)2(aq)

B.B ? S.S ? penalize ? mk

S.S ? B.B ? penalize fully

Chamber II

2NH4Cl(aq) + Ca(OH)2(aq)

2NH3(g) + CaCl2(aq) + 2H2O(l)

(allow rules of balancing equation)

c) - Used as a drying agent when in anhydrous form for gases that do not react with it

- Used during extraction of sodium metal from sodium chloride to lower the melting point of electrolyte from 8000C to 6000C

(award 1mk for any one above)

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d) Ammonia

Carbon (IV) oxide

e) - Glass making

- In pulp and paper industry

- Manufacture of sodium silicate

- Water softening

- Cattle lick

(Any two above, award 1mk)

f) i) Excess supply of oxygen/ air 1

ii) Limited supply of oxygen / air 1

iii) Bubble each gas separately through calcium hydroxide solution 1 carbon (IV)

oxide forms a white precipitate while carbon (II) oxide does not 1

3. a) Molar heat of fusion is the amount of heat energy required to convert one mole of a solid

substance at its melting point into a liquid.

b)i)

The heat of neutralization for reaction (I) is higher than that of II. Reaction I

involves hydration energy for K+ and OH- ions and neutralization energy while

reaction II involves only neutralization energy ii) Reaction a Mg2+ is a smaller ion than Ca2+.Hence Mg2+ ion form stronger forces of

attraction with water than Ca2+ ion during hydration.

iii) Ignition provides activation energy for the combustion reaction to begin.

c) a) Hess's law states that the energy change in converting reactants to products is the same regardless of the route by which the chemical change occurs. 1

b) Zinc is more reactive than copper, hence displaces it from solution 1 Zn is a stronger reducing agent than copper

i)

Zn(s) + Cu2+(aq)

B.B + S.S ? award fuly

Zn2+(aq) + Cu(s)

B.B ? S.S ? penalize ? mk

S.S ? B.B ? penalize fully

ii) H1 +- 57 = -227

H1 = - 227 + 57 H1 = -170kJ mol -1

4. a) i) Solution A

Name sodium hydroxide ?

Formula NaOH ?

ii) Zinc Hydroxide ?

Formula: Zn(OH)2 ?

b) i)

Zn(s) + H2SO4(aq)

ZnSO4(aq) + H2(g)

B.B + S.S ? award fuly

B.B ? S.S ? penalize ? mk

S.S ? B.B ? penalize fully

ii) Zn(OH)2(g) + 2HCl(aq)

ZnCl2(aq) + 2H2O(l)

c) Introduce a burning splint to the gas jar full of hydrogen gas ? It burns with a `pop'

sound ?

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d) - Sodium metal darts on the surface of the water - A hissing sound is produced 1

e) i) Heat solution E over a water bath to evaporate excess water; when crystals are almost forming remove from fire and leave it to cool slowly 1

ii) Heat the solution directly until all the water has evaporated to remain with a white powder of Zinc chloride 1

f)

Zn(s) + 2HCl(aq)

ZnCl2(aq) + H2(g)

5. a)

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i) 14 minutes ?

(showing of the graph ? )

ii) Carbonate was used up / consumed 1 iii) 480cm3 1

b) i)

MCO3(s) + 2HNO3(aq)

M(NO3)2(aq) + CO2(g) + H2O(l)

B.B + S.S ? award fuly

B.B ? S.S ? penalize ? mk

S.S ? B.B ? penalize fully ii) If 480cm3 given by 2.5g 1

24000cm3 will be given by

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24000 x 2.5 480 = 125g ? iii) MCO3(s) = 125g M + 12 + 48 = 125g ? M = 125 ? 60 M = 65 ?

4 6. a) P ? alpha / / He ?

2

Q ? Gamma /

o

e R ? Beta /

?

1

b) i) Nuclear reactions involve the protons and neutrons while chemical reactions

involve electrons 1

ii) Nucleas reactions are not affected by external factors such as temperature while

chemical reactions are affected 1

12

14

c) i)

C and C 1

6

6

ii)

14 14 o C N

1

6

7 1

iii) Carbon dating 1

d) i) Half ? life ? Time taken for any amount of a radioactive substance to decay to half

the initial mass 1 ii) 25g 1st 12g5g 2nd 6g 25g 3rd 3.125g

No of half lifes = 3 1 half - life = 6/3 = 2hrs 1

e) - Treatment of cancer

- To detect blood circulation disorders

- To study the condition of thyroid gland (Any 2 x 1 = 2mks)

7. a) i) A and E 1

ii) C, D, E

(any 2 award 1mk each)

b) i)

D3+ is smaller than E 2+ 1 D3+ has a greater nuclear charge ? thus greater

attraction ? electrons.

ii) E is more reactive than A 1

E has a larger atomic radius ? hence outermost electrons are more loosely

held ? hence easily lost than those of A.

c) i) C ? 2.8.6 ?

ii) D ? 2.8.3 1

d) i)

EB2 1

Reject B2E ii) Ionic /electrovalent ?

- It involves transfer of electrons from A to oxygen ?

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