Chemistry Past Questions and Answers

Which of the compounds will leave a metal residue when heated?

A visible change is observed when a strip of iron is placed in an aqueous solution of

(a) State three characteristic properties of<br/>(i) electrovalent compounds;<br/>(ii) alpha particles<br/>(iii) catalysts<br/> <br/>(b)(i) Write the electronic configuration of silicon (atomic number 14) and state the group to which it belongs in the Periodic Table.<br/>(ii) State the type of chemical bonding between silicon and oxygen in SiO\(_2\)<br/>(iii) A chip used in a microcomputer contains 5.72 x 10\(^{-3}\)g of silicon, calculate the number of silicon atoms in the chip.<br/>[Si = 28; Avogadro constant = 6.02 x 10\(^{23}\) mol\(^{-1}\)]<br/> <br/>(c) An element X belongs to the same group as sodium but is more reactive.<br/>(i) Suggest with reason whether X would be a reducing or oxidizing agent.<br/>(ii) What would be a suitable method of storing X in the laboratory?<br/>(iii) Describe briefly what would be observed if a small piece of X were dropped into a trough of cold water which had been coloured with red litmus.<br/>(iv) Write an equation to show how the oxide of X would react with dilute HCI.<br/>(v) Suggest the likely colour of the salts of X

(a)(i) Explain what is meant by acid anhydride and give one example<br/>(ii) State three chemical properties of hydrochloric acid.<br/> <br/>(b) Explain each of the following observations:<br/>(i) Tetraoxosulphate (VI) acid can form two types of salts unlike trioxonitrate (V) acid.<br/>(ii) Copper and iron react with concentrated H\(_2\)SO\(_4\) but only one of them reacts with the dilute acid.<br/>(iii) On adding dilute H\(_2\)SO\(_4\) separately to zinc dust and zinc granules of the same mass, the dust produced more vigorous effervescence.<br/> <br/>(c)(i) Define activation energy.<br/>(ii) Sketch and label an energy profile diagram for the following reaction: A + B --> C + D; AH = xkJmol\(^{-1}\)<br/>(iii) Explain why the heat of reaction of the mineral acids with sodium hydroxide is constant in value.<br/> <br/>(d) Consider the reaction represented by the following equation:<br/>Q\(_{(s)}\) \(\rightleftharpoons\) Q\(_{(l)}\) \(\Delta\) = xkJmol\(^{-1}\)<br/>(i) State with reason which of Q\(_{(s)}\) and O\(_{(J)}\) has the higher entropy.<br/>(ii) What will be the effect of decrease in temperature on the system at equilibrium?

(a)(i) Draw and label a simple cell for the electrolytic purification of copper.<br/>(ii) Write can equation for the reaction at each electrode in (a)(i) above.<br/>(iii) State with reason whether the Daniell cell is an electrolytic cell or an electrochemical cell.<br/>(iv) What is the function of MnO\(_2\) in the Laclanche cell?<br/> <br/>(b) Consider the following equation: MnO\(^-_4\) + 8H\(^+\) + xe\(^-\) \(\to\) Mn\(^{2+}\) + yH\(_2\)O. State the<br/>(i) values of x and y;<br/>(ii) oxidation state of Mn in MnO\(^-_4\).<br/> <br/>(c)(i) List three factors that affect selective discharge of ions during electrolysis<br/>(ii) State Faraday's second law of electrolysis.<br/>(iii) A voltameter containing silver trioxonitrate(V) solution was connected in series to another voltameter containing copper (II) tetraoxosulphate(VI) solution. When a current ri 0.200 ampere was passed through the solutions, 0.780g of silver was deposited. Calculate the<br/>I. mass of copper that would be deposited in the copper voltameter<br/>II. quantity of electricity used and the time of current flow. [Cu = 63.5 ; Ag = 108; 1F = 96500C]