WAEC Chemistry 2009 Past Questions

(a)(i) Outline a suitable procedure for the preparation of ZnCl\(_2\) crystals stating from zinc granules.

(ii) Write a balanced equation for the reaction in (a)(i).

(b) Considei' the following solutions: Na\(_2\)SO\(_{4(aq)}\), CH3COOK\(_{(aq)}\), Pb(NO\(_3\))\(_{2(aq)}\) and MgCl\(_2\). Which of them has/have a pH

(i) greater than 7;

(ii) equal to 7;

(iii) less than 7?

(c)(i) Determine the oxidation number of Mn in I. MnO\(_2\); II. KMnO\(_4\).

(ii) State one laboratory use of each of the .compounds in (c)(i).

(d) Explain why oxidation and reduction processes are complementary.

(e) Consider the reaction represented by the equation: Fe\(_{(s)}\) + 2Ag\(^+_{(aq)}\) \(\to\) Fe\(^{2+}_{(aq)}\) + 2Ag\(_{(s)}\)

(i) Write a balanced ionic half equations for the reaction.

(ii) Which of the species is I. oxidized; II. reduced?

(iii) State the change in the oxidation number of silver during the reaction.

(a) (i) State Boyle's law.

(ii) Give the mathematical expression of Boyle's law.

(iii) Sketch the graphical representation of Boyle's law.

(b) A given mass of gas occupied 500 cm3 at 30°C and 6.5 x 104 Nm\(^{-2}\). Calculate the volume of the gas at s.t.p. [ Standard pressure = 1.01 x 105 Nm\(^{-2}\)]

(c) Explain why an inflated balloon expands in warm water.

(d)(i) What is meant by the term vapour density? (ii) Determine the vapour density of SO\(_{2}\). [ S = 32, O = 16 ]

(e)(i) Which of the following gases, SO\(_{2}\) and NH\(_{3}\) can be collected by I. upward delivery; II. downward delivery?

(ii) What would be the nature of the solution formed by dissolving each of the following substances in water separately. I. SO\(_{2}\) II. NH\(_{3}\)

(iii) State the property exhibited by SO\(_{2}\) and NH\(_{3}\) in the following equations:

I. 2H\(_{2}\)S\(_{(aq)}\) + SO\(_{2(g)}\) \(\to\)  3S\(_{(s)}\) + 2H\(_{2}\)O\(_{(/)}\)

II. 3CuO\(_{(s)}\) + 2NH\(_{3(g)}\)  \(\to\) 3Cu\(_{(s)}\) + 3H\(_{2}\)O\(_{(/)}\) + N\(_{2(s)}\).

(f) State two alloys of tin.

(ii) Give one use of each of the alloys in (f)(i).

(a)(i) Define polymerization.

(ii) Mention two types of polymerization.

(iii) Give one example of I. naturally occurring polymer, II. synthetic polymer.

(b)(i) Describe how ethyne could be prepared in the laboratory.

(ii) Write an equation for the I. polymerization of ethyne II. complete reaction of ethyne with hydrogen bromide.

(iii) Name each of the products formed in (b)(ii) II.

(c)(i) Define each of the following terms: I. pollution; Il. pollutant.

(ii) Mention three types of pollution.

(iii) Give two ways by which pollution can be prevented.

(a) Atoms of four non-metallic elements in the same group of the periodic table are arranged in order of increasing atomic radius as R < T < W < X. Which of the elements

(i) would readily lose electron(s) from the outermost shell;

(ii) is most electronegative;

(iii) would T displace from aqueous solution;

(iv) is at the top of the group?

(b) The following table shows the electronic configuration of two elements Y and Z.

(i) Name the I. group to which Y belongs II. period to which Z belongs.

(ii) What is the number of protons present in an atom of Z?

(iii) How many unpaired electrons are in an atom of Y?

(iv) Write the formula of the compound formed between Y and Z

(c) Name the type of bond(s) that exist(s) in each of the following compounds.

(i) CaCl\(_2\); (ii) NH\(_4\)Cl; CCl\(_4\)

(d) Describe how the conductance of a molar solution of ammonia compares to that of sodium hydroxide solution.

(e) State the type of reaction illustrated by each of the following equations:

(i) CH\(_3\)CH\(_2\)OH\(_{(/)}\) + CH\(_3\)COOH\(_{(aq)}\) \(\rightleftharpoons\) CH\(_3\)COOC\(_2\)H\(_5\)\(_{(/)}\) + H\(_2\)O\(_{(/)}\)

(ii) H+\(_{Y^+_{(aq)}\) + OH\(^+_{(aq)}\) \(\to\) H\(_2\)O

(f) Determine the volume of the residual gas when 20.0cm\(^3\) of hydrogen was sparked with 15.0cm\(^3\) of oxygen and the resulting mixture cooled to room temperature.

 (a)(1) Define each of the following terms: I. deliquescence; II. efflorescence.

(ii) Give one example I substance that undergoes each of the processes in (a)(i).

(b) Outline how three colourless gases suspected to be ethane, ethene and ethyne could be distinguished in the laboratory.

(c)(i) What is water crystallization?

(ii) Hydrated calcium chloride (CaCl\(_2\) = 111, xH\(_2\)O) contains 49.32% water of cystallization. Calm the value of x. [ (CaCl\(_2\) = 111, H\(_2\)O = 18 ]

(d) Name one calcium compound used (i) in the manufactur cement; (ii) as a dessicant; (iii) in the production of plaster of Paris (POP);

(iv) to neutralise acidic soils

(e) A concentrated solution of sodium chloride was electrolysed using graphite electrodes.

(i) State the ions present in the solution

(ii) Name the products at the I. anode, II. cathode.

(iii) Give the by-product of the electrolysis.

(a) State Gay Lussac's Law.

(b) Carbon (II) oxide reacted with oxygen to form carbon (IV) oxide in a see tube.

(i) Write a balanced equation for the reaction.

(ii) If 40 cm\(^3\) of the carbon (II) oxide were mixed with cm\(^3\) of oxygen,

I. calculate the volume of carbon (IV) oxide produced

II. which reactant is in excess and how much?

III. what was the total volume of the gaseous mixture at the end of the reaction?

(c) Consider the following oxides: CaO, SiO\(_2\), CO, NO\(_2\) and ZnO. Which of the oxide(s) 

(i) is an acidic oxide that is insoluble in water?

(ii) reacts with water to give alkaline solution?

(iii) is amphoteric?

(iv) is neutral?

(v) is/are gaseous at room temperature?

(d) Explain why

(i) colourless concentrated trioxonitrate (V) acid turns yellow,

(ii) dilute trioxonitrate (V) acid does not liberate hydrogen when it reacts with magnesium.

(e) Write a chemical equation for the thermal decomposition of (i) Cu(NO\(_3\))\(_{2(g)}\)

(ii) NH\(_4\)NO\(_{3(g)}\)