3(a)(i) and (ii): This question was attempted by majority of the candidates and the performance was poor. In this section most candidates were unable to correctly define nuclear fission. Most candidates omitted the word “heavy” nucleus and ‘large’ energy in the definition. Most candidates could not write the balanced nuclear equation but mention the numbers of alpha and beta particles emitted.
In b(i), (ii) and (III) majority of the candidates were not able to respond appropriately to questions on equilibrium. Most candidates lost marks by not further stating the effect of each increase, decrease and addition of catalyst.
In (c) majority of the candidates had no answer to this. In (d)(i) and (ii) most candidates got (i) correctly but lost mark in (ii) because they only mention oxidizing agents.
In (e) most candidates lost marks because they could not identify the equation at the top, middle and bottom of the furnace.
In (f) most candidates correctly name two product of the destructive distillation of coal and gave one use of each product.
The expected answers were:
(a) (i) Is the splitting up of heavy nucleus into smaller nuclei accompanied by
the release of large amount of energy
(ii) Let x and y represent number of alpha and beta particles emitted respectively.
U Th + x He + y e
By inspection
u Th + 2 He + 2 e
\ a particles = 2
Beta particles = 2
(b) (i) Equilibrium position shifts to the right and more of AB3 is formed/
decrease in concentration of A2.
(ii) Equilibrium shift to the left and more of A2 and B2 formed/ decrease in concentrate of AB3
(iii) No effect. Catalyst affects both forward backward reactions equally.
(c) For a constant cation Na+, lattice energy decreases with increase in size of the anion/ decrease in electronegativity of anion.
F-,Br-, I- increasing order of size. Hence the decreasing order of lattice energy.
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(d) (i) NO2 is an oxidizing agent.
(ii) NO2 is acting as an oxidizing as well as reducing agents or acid anhydride.
(e) (i) Fe2O3 + 3CO ® 2Fe + 3CO2
(ii) CaCO3 ® CaO + CO2
CaO + SiO2 ® CaSiO3
(iii) C + O2 ® CO2
CO2 + C ® 2CO
(f) (i) Coke/Coal tar/Coal gas/Ammonical liquor
(ii) Coke - solid fuels/production of water gas, extraction of metals.
Coal tar - synthesis of chemicals - perfumes, dyes, paints, drugs, plastic and explosives etc.
Coal gas - as fuels in homes and industries.
Ammonical liquor - production of (NH4)2 SO4 for fertilizer.