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2012 WAEC Chemistry Theory (a) (i) Define nuclear fission. (ii) A certain natural decay series starts with \(^{238}_{92}U\) and...

Chemistry
WAEC 2012

(a) (i) Define nuclear fission.

(ii) A certain natural decay series starts with \(^{238}_{92}U\) and ends with\(^{230}_{90}Th\). Each step involves the loss of an alpha or a beta particle. Using the given information, deduce how many alpha beta particpes were emitted.

(b) Consider the equilibrium reaction represented by the following equation:

A\(_{2(9)}\) + 3B\(_{2(9)}\) \(\rightleftharpoons\) 2AB\(_{3(g)}\); \(\Delta\)H = + xkJmol\(^{-1}\)

Explain briefly the effect of each of the following changes on the equilibrium composition: (i) increase in concentrat of B; (ii) decrease in pressure of the system; (iii) addition of catalyst.

(c) The lattice energies of three sodium halides are as follows:

Compound

NaF NaBr

Nal

Lattice energy/kJmol\(^{-1}\)

890 719 670

Explain briefly the trend.

(d) State the property exhibited by nitrogen (IV) oxide in each of the following reactions:

(i) 4Cu + 2NO\(_2\) \(\to\)  4CuO + N\(_2\);

(ii) H\(_2\)O +  2NO\(_2\) \(\to\) HNO\(_3\) + HNO\(_2\).

(e) Iron is manufacturcd in a blast furnace using iron ore (Fe\(_2\)O\(_3\)), coke and limestone. Write the equation for the reaction(s) at the: (i) top of the furnace; (ii) middle of the furnace; (iii) bottom of the furnace.

(f) (i) Name two products of destructive distillation of coal. (ii) Give one use of each product in (f)(i).

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Explanation

(a)(i) It is the splitting of a heavy nucleus into smaller nuclei accompanied by the release of large amount of energy.

(ii)\(^{238}_{92}U\) and ends with\(^{230}_{90}Th\) + \(2^{4}_{2}He\)  + \(2^{o}_{-1e}Th\)

\(\alpha\) [articles = 2

\(\beta\) particles = 2

 

(b)(i) Equilibrium positicn shifts to the right and more of AB\(_3\) is formed or decrease in concentration of A\(_2\)

(ii) Equilibrium shifts to the left and more of A\(_2\) and; B\(_2\) formed / decrease in concentration of AB\(_3\)

(iii) No effect. Catalyst affects both forward and backward reactions equally.

 

(c) For a constant cation Na\(^+\) lattice energy decreases with ircreases in size of the anion / decrease in electronegativity of the anion.

F\(^-\), Br\(^-\),  I\(^-\) increasing order of size. Hence the decreasing crder ofilattice energy.

 

(d)(i) NO\(_2\) is an oxidizing agent

(ii) NO\(_2\) is acting as an oxidizing as well as reducing agents OR acid anhydride.

 

(e)(i) Fe\(_2\) O\(_3\) + 3CO --> 2Fe + 3CO\(_2\)

(ii) CaCO\(_3\) —› CaO + CO\(_2\), CaO + SiO\(_2\)  \(\to\) CaSiO3

(iii) C + O\(_2\) —> CO\(_2\), CO\(_2\) + C \(\to\) 2CO

 

(f) Coke I Coal Tar / Coal Gas /Ammonical Liquor

(ii) Coke — Solid fuels I production of water gas, extraction of ME 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 (NH\(_4\))\(_2\) SO\(_4\) for fertilizer


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