Chemistry Past Questions and Answers

(a)Give two reasons why aluminium is preferred to copper for making overhead electric cables.<br/>(ii) Describe briefly the electrolytic extraction of aluminium from purified bauxite.<br/> <br/>(b) The diagram below represents an electrolytic cell used for the purification of copper.<br/>(i) Which of the electrodes I and II increases in mass during the electrolysis? Give reasons for your answers<br/>(ii) State with reason the site of oxidation<br/>(iii) Identify III and explain why its colour does not change in intensity during the electrolysis.<br/> <br/>(c) Calculate the current in amperes that will deposit 8.00 g of calcium from used CaCl\(_2\) in 1 hour 15 minutes. [Ca = 40.0; 1 Faraday = 96500C]

(a) Mention one oxide in each case, which<br/>(i) used in bleaching<br/>(ii) is a redish-brown gas<br/>(iii) reacts with NaOH and also with HCI;<br/>(iv) dissolves in water to give a solution with pH greater than 7;<br/>(v) oxidizes hot, concentrated HCI to chlorine<br/> <br/>(b)(i) State three methods that can be used to removo hardness in a sample of water that contains calcium hydrogentrioxocarbonate (IV).<br/>(ii) Explain with the aid of appropriate equation, why it is not advisable to build a house with limestone in an environment polluted by sulphur (IV) oxide.<br/> <br/>(c)(i) List two compounds of potassium which yield oxygen when heated strongly<br/>(ii) Calculate the amount (in moles) of gas which occupies 250 cm\(^3\) at s.t.p. [1 mole of gas occupies 22.4 dm\(^3\) at s.t.p]<br/>(iii) If 250 cm\(^3\) of a gas at s.t.p. is heated to 27°C at constant pressure, calculate its new volume.<br/>(iv) Explain in terms of the collision theory what happens as a gas is heated at constant pressure.

The mass of an element is 27 and its atomic number is 13. What is the composition of the nucleus of its atom?

Which of the following electron transition results in the emission of energy?

Which of the following properties of elements deceases generally across a period in the Periodic Table?