Waec Chemistry 2012 Past Questions and Answers

Question 46:

• WAEC 2012

(a) (i) What is the structure of the atom as proposed by Rutherford?
(ii) Distinguish between the atomic number and the mass number of an element.
(iii) Explain briefly why the relative atomic mass of chlorine is not a whole number.

(b) (i) What is meant by first ionization energy?
(ii) List three properties of electrovalent compounds.
(iii) Consider the following pairs of elements: I. \(_9\)F and \(_{17}\)Cl; \(_{12}\)Mg and \(_{20}\)Ca. Explain briefly why the elements in each pair have similar chemical properties.

(c) Explain briefly the following terms using an appropriate example in each case.
(i) homologous series; (ii) heterolytic fission.

(d) State the indicator(s) which could be used to determine the end-point of the following titrations:
(i) dilute hydrochloric acid against sodium hydroxide solution;
(ii) dilute hydrochloric acid against ammonium hydroxide solution;
(iii) ethanoic acid against sodium hydroxide solution.

(e) A solid chloride E which sublimed on heating reacted with an alkali F to give a choking gas G. G turned moist red litmus paper blue. identify E, F and G.

Question 47:

• WAEC 2012

(a) (i) What is diffusion?
(ii) State Charles' law:
(iii) Sketch a graph to illustrate Charles' law.
(iv) A given mass of a gas occupied 150 cm3 at 27 °C and a pressure of 1.013 x 105 Nm\(^{-2}\). Calculate the temperature at which its volume will be doubled at the same pressure.
(v) Arrange the three states of matter in order of increasing: (i) kinetic energy; (ii) forces of cohesion.
(b) (i) State Le Chatelier's principle. (ii) A metal M forms two oxides containing 11.1% and 20.0% of oxygen. Show that these figures agree with the law of multiple proportion.
(c) The table below shows the physical properties of substances A, B and C.

Substance	Melting point/°C	Boiling point/°C	Solubility in water at 25°C
A	30	117	Insolube
B	31	160	Insoluble
C	1200	1200	Insoluble

(i) If A and B are miscible when melted and B and C react when heated, describe how a mixture of A, B, and C could be separated.
(ii) When 25.25g of the mixture A, B and C was separated, 7.52 g of A and 8.48 g of B were recovered. Assuming i there was no loss of components during separation, calculate the percentage by mass of C in the mixture

Question 48:

• 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).

Question 49:

• WAEC 2012

(a) (i) What is a structural isomer?
(ii) Write all the structural isomeric alkanols with the molecular formula C\(_4\)H\(_{10}\)O.
(iii) Which of the isomers from (a)(ii) above does not react easily on heating with acidified K\(_2\)Cr\(_2\)O\(_7\)?
(b) Chlorine reacted with excessentane in the presence of light. Chloropentane and a gas which fumes on cont with air were produced.
(i) Write an equation for the reaction.
(ii) Draw the structure of the major product.
(iii) What is the role of light in the reaction?
(iv) If a mixture of pentane and the major product is heated, which compounc would distil off first? Give a reason for your answer.
(v) Write the formula of the main product that would have be formed if but -1-ene has been used instead of pentane.
(c) Give the name and structural formula of the product which would be formed by hydration of each of the followinc compounds:
(i) CH\(_3\)CH(CH\(_3\))CH=CH\(_2\); (ii) CH\(_2\)=CHCOOH.
(d) (i) Write the structure of the amino acid, CH\(_3\)CH(NH\(_2\))COOH in: I. acidic medium; II. alkaline medium.
(ii) On analysis, an ammonium salt cf an alkanoic acid gave 60.5% carbon and 6.5% hydrogen. If 0.309 g of the salt yielded 0.0313 g of nitrogen, determine the empirical formula cf the salt. [H = 1.00; C =12.0; N =14.0; O = 16.0]

Question 50:

• WAEC 2012

(a) (i) Define standard electrode potential.
(ii) State two factors that affect the value of standard electrode potential.
(iii) Give two uses of the values of standard electrode potential.
(iv) Draw and label a diagram for an electrochemic cell made up of Cu\(^{2+}\)/Cu; E° = +0.34 V Zn\(^{2+}\)/Zn; E° = -0.76 V
(v) Calculate the e.m.f. of the cell in (a)(iv) above.
(b) (i) In terms of electron transfer, define: I. oxidation; II. oxidizing agent.
(ii) Balance the following redox reaction: MnO\(^{-4}\) + l\(^{-}\) \(\to\) l\(_{2}\) + Mn\(^{2+}\)
(c) Classiify each of the following oxides as basic, amphoteric, acidic or neutral: (i) Carbon (II) oxide; (ii) Sulphu (IV) oxide; (iii) Aluminium oxide; (iv) Lithium oxide.
(d) What is hydrogen bonding?