WAEC Chemistry 2004 Past Questions

(a)(i) Mention two types of bond present in the ammonium ion

(ii) Give three characteristic properties of electrovalent compounds

(iii) State. two differences between chemical reactions and nuclear reactions

(b) Two elements represented by the letters and Y have atomic numbers 9 and 12 respectively.

(i) Write the electronic configuration of X using the s,p,d, notation

(ii) To what group does Y belong in the periodic table?

(iii) Write the formula of the compound formed when X copibines with Y

(iv) Explain wily X is a good oxidizing agent

(v) State with reason, whether Y would be expected to form acidic or basic oxide

(c) Balance the following nuclear equations and identify the particles represented by X and Y.

(i) \(^{14}_6C\) \(\to\) X + \(^{14}_7N\)

(ii) \(^{14}_7C\)

Y \(\to\) \(^1_1H\) + \(^{17}_8O\)

(d) Consider the following list of substances: Carbon (IV) oxide, hydrogen, zinc, sulphier, methane, potassium and mercury. From the list above, state the:

(i) elements that are metals

(ii) compounds that are gases at room temperature

(iii) non-metals that are solids at room temperature

(i) State Two assumptions of the kinetic theory of gases

(ii) When some solids are heated, they change directly into the gaseous state. What narne is given to this phenomenon?

(iii) List two substances which exhibit the phenomenon referred to in (a)(ii) above

(iv) Write an expression to show the mathematical relationship between the rate of diffusion of a gas and its vapour density.

(b) Consider the following equilibrium reaction:

3Fe\(_{(s)}\) + 4H\(_2\)O\(_{(g)}\) \(\rightleftharpoons\) FeO\(_3\)O\(_{4(s)}\) + 4H\(_{2(g)}\), \(\Delta\)H = - 150KJ mol\(^{-1}\)

Explain the effect of the following factors on the position of equilibrium: (i) tecrease in temperature; (ii) Increase in pressure; (iii) Removal of hydrogen.

(c) . Three beakers labelled P, Q and S each contained zinc metal of the same mass but in different forms. P contained a length of zinc rod, Q contained zinc dust while S contained zinc foil. 100cm\(^3\) of 5.0 mol dm\(^{-3}\) hydrochloric acid was added to each beaker to react with all the zinc.

(i) State the order in which the reaction came to completion in beakers P,Q and S starting with the fastest.

(ii) Give reason for your answer in (c)(i) above

(iii) Write an equation to represent the reaction between zinc rid the hydrochloric acid.

(d) (i) What is meant by pH of a solution?

(ii)(I) State with reason in each case whether the pH would increase, decrease or remain constant if the following experiments were carried out Neutralizing bench HNO\(_3\);

II. Diluting 25.0 cm\(^3\) of a given NaOH solution to 100.0cm\(^3\) Concentrating a solution of NaCI.

(a) Draw an energy profile diagram to illustrate a catalysed exothermic reaction and label parts of the curves representing the following:

(i) activated complex (without catalyst);

(ii) activated energy (with catalyst)

(iii) enthalpy change

(b) Give the reasons for the following observations:

(i) A balloon filled with liyilrogen becomes deflated faster than a balloon filled with air under the same conditions.

(ii) Hydrogen peroxide decomposes slowly at room temperature but when a pinch of MnO, is added, bubbles form rapidly.

(iii) A solution of hydrogen chloride as in methylbenzene has no effect on `litmus but a solution of the gas in water turns blue litmus paper red.

(c) Consider the reaction represented by the following equation: 2MnO\(^-_{4(aq)}\) + 5C\(_2\)O\(^{2-}_4\) + 16H\(^+\) \(\to\) 2Mn\(^{2+}_{(aq)}\) + 8H\(_2\)O\(_{(l)}\) + 10C\(_{2(g)}\) .

Write down: (i) the species undergoing reduction giving reasons;

(ii) the reducing agent giving reasons;

(iii) the reduction half equation;

(iv) one observation made during the reaction.

(d)(i) What is an electrochemical cell?

(ii) State three differences between an electrochemical cell and an electrolytic cell.

(a) Methane reacts with chlorine under certain condition to produce tetrachloromethane.

(i) State the condition for the reaction

(ii) Name the type of reaction

(iii) Give two uses of methane

(iv) Name one major natural source of methane

(b)(i) Mention one similarity between the reaction of ethanol with sodium and that of sodium with water

(ii) Write the structure of two isomers of C\(_3\)H\(_8\)O

(iii) Differentiate between a fine chemical and a heavy chemical

(iv) Give one example of each in (b)(iii) above

(c) Two compounds X and Y have the same percentage composition by mass of 92.3% carbon and 7.7% hydrogen. Calculate the:

(i) empirical formula of X and Y;

(ii) molecular formula of each compound if molar mass of X is 26 g and Y is 78g.

(d) A protein is boiled for a long time with dilute HCI and a reaction occurred.

(i) State the type of reaction that occurred

(ii) Name the major product formed

(iii) Give the functional groups present in (d)(ii) above.

(a)(i) State one physical method and one chemical method in each case by which the following can be removed:

I. Permanent hardness in water

II. A suspension of CaCO\(_3\) in water.

(ii) Give one disadvantage of hard water.

(b) Explain the following observations: (i) Crystals of washing soda become powdery on exposure to air for a long time

(ii) The concentration of chloride ions in 0.02 mol dm\(^{-3}\) calcium chloride solution is not the same s in 0.02 mol dm\(^{-3}\) sodium chloride solution.

(iii) Iron filings corrode faster than iron nails of the same mass.

(c)(i) Classify each of the following oxides as acidic, basic, neutral or amphoteric. I. ZnO II. CO III. NO\(_2\)

(ii) Give the formula of the acid anhydride of each of the following: I. H\(_2\)CO\(_3\) II. H\(_2\)SO\(_4\)

(iii) Give the IUPAC name of the following salts: I. COCl\(_2\) II. Mg(NO\(_3\))\(_2\).

(d)(i) Mention one pollutant associated with depletion of ozone layer in the atmosphere

(ii) Calculate the volume occupied by 0.125 mole of oxygen at 27°C and a pressure of 2.02 x 105 Nm\(^{-2}\) [I mole of gas occupies 22.4 dm\(^3\) at s.t.p; standard pressure = 1.01 x 105 Nm\(^{-2}\)]

(iii) State one process used for the industrial preparation of oxygen.

(a)(i) Give the reason why copper turnings dissolve in AgNO\(_3\) solution but remain insoluble in Pb(NO\(_3\) )\(_2\) solution.

(ii) Copper turnings of mass 1.06g were placed in 250 cm\(^3\) of 0.20 mol dm\(^{-3}\) AgNO\(_3\). Calculate the amourt of silver ions present. [Cu = 63.5]

(iii) Determine whether all the copper in (a)(ii) above will discolvo in the solution. The equation for the reaction is CU\(_{(S)}\) + 2Ag\(^+_{(aq)}\) --> Ag\(_{(aq)}\) + Cu\(^{2+}_{(aq)}\)

(b)(i) List cheicil properties of acids

(ii) Give two large scale uses of HNO\(_3\)

(iii) Write an equation for the action of heat on each of the following compounds: I. Pb(NO\(_3\))\(_2\)

Il. AgNO\(_3\).

(c)(i) State what would be observed if a piece of damp blue litmus paper is dropped into a glass jar of chlorine.

(ii) Name the type of reaction which occurs in (c)(i) above.

(iii) Give the property of chlorine which is exhibited in the reaction in (c)(i) above.

(i) Name two products obtained directly from the destructive distillation of coal.

(ii) Give one use of each product named in (d)(i) above.