Chemistry Past Questions and Answers

The greenhouse effect is a climatic condition associated with the presence of excess

(a)(i) State three postulates of the kinetic theory of gases.<br/>(ii) Draw a sketch to illustrate Boyle's law.<br/>(iii) Explain what is meant by "absolute zero of temperature".<br/>(b) Equal volumes of a gas X and oxygen are at the same pressure but temperature of 200 K and 800K respectively.<br/>(i) Giving reason for your answer, state which of the gas samples contains the greater number of molecules.<br/>(ii) If the mass of one molecule of the gas X is 2.19 x 10\(^{-22}\) g, determine the molar mass of X. [Avogadro constant = 6.02 x 10\(^{-23}\)]<br/>(iii) Hence, state with reason which of X and oxygen will diffuse faster under the same conditions. [O= 16].<br/>(c)(i) Mention two reaction conditions that can increase the yield of ammonia in the reaction represented by the following equation: N\(_{2(g)}\) + 3H\(_{2(9)}\) \(\rightleftharpoons\) 2NH\(_{3(g)}\) \(\Dellta\)H = -46kJmol\(^{-1}\). Draw a labelled energy profile diagram for an endothermic reaction.<br/>(iii) A solid W decomposes on heating according to the following equation: W\(_{(s)} \to Y_{(s}) + Z_{(g)}\) List two factors apart from temperature, which can affect the rate of the reaction.

a)(i) State three differences between covalent compounds and electrovalent compounds.<br/>(ii) Two elements represented as K and L have atomic numbers of 12 and 8 respectively. Write their electronic structures and state the group to which each belongs in the Periodic Table.<br/>(iii) If an alkali metal M exists naturally as the oxide, state with reason whether or not M can be extracted by reduction of the oxide with coke.<br/> <br/>(b)(i) What is meant by the half-life of a radioactive element?<br/>(ii) Mention the radioactive isotope used in dating archaeological specimens.<br/>(iii) Balance the following equation and identify Q,<br/>\(^{28}_{13}Al\) –> \(^{24}_{13}Si + \(^{0_1Q\)<br/> <br/>(c)(i). Give three chemical properties of metals.<br/>(ii) State two reasons why duralumin preferred to steel in aircraft manufacture.<br/>(iii) What term is used to describe the ability of metals to be hammered into thin sheets?<br/>(iv) Calculate the number of mole of electrons involved in the oxidation of 2.8g of iron filings to iron (II) ions. [Fe = 56].

(a) The letters R,S,T represent an alkene, an alkene and a terminal alkyne respectively. Which of R, S and T typically undergo(es) the following reactions?<br/>(i) Addition reaction;<br/>(ii) Combustion;<br/>(iii) Substitution reaction.<br/> <br/>(b)(i) Name the process by which an alkanol can be converted to an alkene.<br/>(ii) Write the name and structural formula of the third member cf the alkanol series.<br/>(iii) State what would be obtained if a primary alkanol reacted with excess acidified KMnO\(_4\) solution.<br/> <br/>(c)(i) Give one chemical test for alkanoic acids.<br/>(ii) Write an equation to show how methanoic acid reacts with ethanol in the presence of mineral acids.<br/>(iii) What is the role of mineral acid in the reaction in (c) ii?<br/> <br/>(d) In an experiment, cassava was pressure-cooked to release starch granules, followed by treatment with malt for about 2 hours at 55°C. Yeast was then added and the mixture was left for 2 days at 27°C. An organic product J and a gas H were obtained.<br/>(i) Identify H<br/>(ii) State the class of carbohydrates to which starch belongs and explain what happened to the starch during treatment with malt.<br/>(iii) Draw a labelled diagram of a suitable set-up for obtaining a sample of J from the reaction mixture.

(a)(i) Give two differences between a conductor and an electrolyte.<br/>(ii) State three applications of electrolysis.<br/>(iii) Write equation for the reaction at each electrode when a dilute solution of sodium chloride is electrolysed using carbon electrodes.<br/>(b)(i) What is an electrochemical cell?<br/>(ii) Give two examples of primary cells.<br/>(iii) Split the following equation into two balanced hall cell equations. Mte + Fe\(^{2+} \to Mg^{2+} + Fe\).<br/>(c)(i) A current of 0.72 amperes was passed through dilute tetraoxosulphate (VI) acid for 3 hours 20 minutes. Calculate the quantity of electricity that was passed<br/>(ii) If 1 dm\(^3\) of gas evolved at the cathode during the electrolysis of acidified water, what was the volume of gas evolved at the anode?<br/>(d)(i) 20g of copper(II) oxide was warmed with 0.05 mole of tetraoxosulphate (VI) acid. Calculate the mass of copper (II) oxide that was in excess. The equation for the reaction: CuO\(_{(s)}\) + H\(_2\)SO\(_{4(aq)}\) ---> CuSO\(_{4(aq)}\) + H\(_2\)O\(_l\) [0 = 16 ; Cu = 64]<br/>(ii) What type of reaction was involved in (d)(i)?