Chemistry Past Questions and Answers

(i) State Two assumptions of the kinetic theory of gases<br/>(ii) When some solids are heated, they change directly into the gaseous state. What narne is given to this phenomenon?<br/>(iii) List two substances which exhibit the phenomenon referred to in (a)(ii) above<br/>(iv) Write an expression to show the mathematical relationship between the rate of diffusion of a gas and its vapour density.<br/> <br/>(b) Consider the following equilibrium reaction:<br/>3Fe\(_{(s)}\) + 4H\(_2\)O\(_{(g)}\) \(\rightleftharpoons\) FeO\(_3\)O\(_{4(s)}\) + 4H\(_{2(g)}\), \(\Delta\)H = - 150KJ mol\(^{-1}\)<br/>Explain the effect of the following factors on the position of equilibrium: (i) tecrease in temperature; (ii) Increase in pressure; (iii) Removal of hydrogen.<br/> <br/>(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.<br/>(i) State the order in which the reaction came to completion in beakers P,Q and S starting with the fastest.<br/>(ii) Give reason for your answer in (c)(i) above<br/>(iii) Write an equation to represent the reaction between zinc rid the hydrochloric acid.<br/> <br/>(d) (i) What is meant by pH of a solution?<br/>(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\(_3\);<br/>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:<br/>(i) activated complex (without catalyst);<br/>(ii) activated energy (with catalyst)<br/>(iii) enthalpy change<br/> <br/>(b) Give the reasons for the following observations:<br/>(i) A balloon filled with liyilrogen becomes deflated faster than a balloon filled with air under the same conditions.<br/>(ii) Hydrogen peroxide decomposes slowly at room temperature but when a pinch of MnO, is added, bubbles form rapidly.<br/>(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.<br/> <br/>(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\(_{2(g)}\) .<br/>Write down: (i) the species undergoing reduction giving reasons;<br/>(ii) the reducing agent giving reasons;<br/>(iii) the reduction half equation;<br/>(iv) one observation made during the reaction.<br/> <br/>(d)(i) What is an electrochemical cell?<br/>(ii) State three differences between an electrochemical cell and an electrolytic cell.

(a) Methane reacts with chlorine under certain condition to produce tetrachloromethane.<br/>(i) State the condition for the reaction<br/>(ii) Name the type of reaction<br/>(iii) Give two uses of methane<br/>(iv) Name one major natural source of methane<br/> <br/>(b)(i) Mention one similarity between the reaction of ethanol with sodium and that of sodium with water<br/>(ii) Write the structure of two isomers of C\(_3\)H\(_8\)O<br/>(iii) Differentiate between a fine chemical and a heavy chemical<br/>(iv) Give one example of each in (b)(iii) above<br/> <br/>(c) Two compounds X and Y have the same percentage composition by mass of 92.3% carbon and 7.7% hydrogen. Calculate the:<br/>(i) empirical formula of X and Y;<br/>(ii) molecular formula of each compound if molar mass of X is 26 g and Y is 78g.<br/> <br/>(d) A protein is boiled for a long time with dilute HCI and a reaction occurred.<br/>(i) State the type of reaction that occurred<br/>(ii) Name the major product formed<br/>(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:<br/>I. Permanent hardness in water<br/>II. A suspension of CaCO\(_3\) in water.<br/>(ii) Give one disadvantage of hard water.<br/> <br/>(b) Explain the following observations: (i) Crystals of washing soda become powdery on exposure to air for a long time<br/>(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.<br/>(iii) Iron filings corrode faster than iron nails of the same mass.<br/> <br/>(c)(i) Classify each of the following oxides as acidic, basic, neutral or amphoteric. I. ZnO II. CO III. NO\(_2\)<br/>(ii) Give the formula of the acid anhydride of each of the following: I. H\(_2\)CO\(_3\) II. H\(_2\)SO\(_4\)<br/>(iii) Give the IUPAC name of the following salts: I. COCl\(_2\) II. Mg(NO\(_3\))\(_2\).<br/> <br/>(d)(i) Mention one pollutant associated with depletion of ozone layer in the atmosphere<br/>(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\(^{-2}\)]<br/>(iii) State one process used for the industrial preparation of oxygen.

The electronic configuration of an element X is 1s<sup style='font-size: smaller;'>2</sup>2s <sup style='font-size: smaller;'>2</sup>2s<sup style='font-size: smaller;'>6</sup>3p <sup style='font-size: smaller;'>2</sup> 3p<sup style='font-size: smaller;'>4</sup>. It can be deduced that X