Chemistry Past Questions and Answers

What are the two gases associated with the formation of acid rain?

Which of the following processes will pollute water?

(a) The electronic configuration of five elements represented by the letters P, Q, R, S and T are indicated below.<br/>P - 1s\(_2\)2s\(_2\)2p\(_2\)<br/>Q 1s\(_2\)2s\(_2\)2p\(_4\)<br/>R 1s\(_2\)2s\(_2\)2p\(_6\)<br/>S - 1s\(_2\)2s\(_2\)2p\(_6\)3s\(_2\)<br/>T - 1s\(_2\)2s\(_2\)2p\(_6\)3s\(_2\)3p\(_5\)<br/><br/>without identifying the elements, state which of them<br/>(i) belongs to group VI in the periodic table;<br/>(ii) is strongly metallic in character;<br/>(iii) readily ionizes by gaining one electron;<br/>(iv) contains two unpaired electrons in the ground state atom<br/>(v) readily loses two electrons during chemical bonding<br/>(vi) Does not paricipates in chemical reactions?<br/>(vii) is an s-block element.<br/> <br/>(b)(i) Copy and complete the table below as appropriate<br/><table class='tbn'><tbody><tr><td> Particle </td><td> Number of Protons </td><td> Number of Electrons </td><td> Number of Neutrons </td></tr><tr><td> \(^1_1H\) </td><td> 1 </td><td> 1 </td><td> </td></tr><tr><td> \(^{27}_{13}\)Al\(^{3+}\) </td><td> </td><td> </td><td> </td></tr><tr><td> \(^{16}_{8}O^{2+}\) </td><td> </td><td> </td><td> 8 </td></tr></tbody></table><br/><br/><br/> <br/>(ii) Give the reason why atomic radius increases down a group in the periodic table but decreases from left to right in a period.<br/> <br/>(c)(i) What is meant by the half-life of a radioactive element?<br/>(ii) The nuclide \(^{210}_{84}PO\) loses an alpha 4° particle to form lead. Write an equation for the reaction.<br/> <br/>(d) State the type of chemical bonding which accounts for each of the following observations:<br/>(i) Chlorine exists as discrete molecules<br/>(ii) Sodium chloride dissolves readily in water;<br/>(iii) CuSO\(_{4(aq)}\) forms a deep blue complex ion with excess NH\(_{3(aq)}\)<br/>

(a) (i) State three characteristic properties of transition metals.<br/>(ii) What is the oxidation state of manganese In each of the following species? (1) MnCl\(_2\) (II) MnO\(_2\) (III) MnO\(_4^{-}\)<br/>(iii) Explain why manganese conducts electricity in the solid state but manganese chloride conducts only when molten or in solution.<br/> <br/>(b)(i) The collision theory suggests that for two particles to react, they must collide. What two factors determine whether or not the collision would lead to formation of products?<br/>(ii) Use an energy profile diagram to illustrate what is meant by the enthalpy change (\(\Delta\)H) and the activation energy (E\(_A\)) of a reaction.<br/> <br/>(c) When few drops of aqueous KSCN are added to a solution of iron (III) salt the following equilibrium is set up:<br/>Fe\(^{3}_{(aq)}\) + 3SCN\(^{-}_{(aq)}\) \(\rightleftharpoons\) Fe(SCN)\(_{3(aq)}\) <br/>yellow colourless deep red<br/>The equilibrium mixture has a pale red colour.<br/>(i) Explain what would happen if more KSCN\(_{(aq)}\) were added to the equilibrium mixture.<br/>(ii) Which of the ions in the equilibrium mixture forms an insoluble hydroxide with NaOH\(_{(aq)}\)? Write an equation for the reaction<br/>(iii) State two changes observed on adding NaOH\(_{(aq)}\) to the equilibrium mixture.<br/> <br/>

(a) i) An organic compound X contains 40% carbon, 6.67% hydrogen, the rest being oxygen. If X has a relative molecular mass of 60, determine its<br/>(i) empirical formula (ii) molecular formula. [H = 1 ; C = 12; O = 16]<br/> <br/>(b) An alkanoic acid Y has a relative molecular mass of 74.<br/>(i) State the functional group of Y<br/>(ii) What t of reaction is involved when Y is converted to an alkanoate?<br/>(iii) Determine the structural formula of Y.<br/>(iv) Write an equation for the reaction between Y and sodium<br/>(v) If X in (a) above boils at 118°C and belongs to the same homologous series as Y, state with reason, whether the boiling point of Y will be equal to, higher or lower than 118°C.<br/> <br/>(c)(i) What is fermentation?<br/>(ii) Write an equation for the fermentation of glucose.<br/>(iii) What must be added to glucose solution to make it ferment?<br/>(iv) Explain why a tightly corked grass bottle filled to the brim with fresh palm wine shatters on standing.