Chemistry Past Questions and Answers

(a)(i) List three properties of elements which increase generally across a period in the Periodic Table,<br/>(ii) Give two differences between a chemical reaction and a nuclear reaction.<br/> <br/>(b) Use the information provided in the table below to answer Questions (i) - (vii).<br/><table class='tbn'><tbody><tr><td> Atom of Element </td><td> P </td><td> Q </td><td> R </td><td> S </td><td> T </td></tr><tr><td> Mass Number </td><td> 16 </td><td> 40 </td><td> 35 </td><td> 18 </td><td> 20 </td></tr><tr><td> Atomic Number </td><td> 8 </td><td> 20 </td><td> 17 </td><td> 8 </td><td> 10 </td></tr></tbody></table><br/><br/><br/><br/>Which of the atoms in the table above:<br/>(i) are isotopes of the same element?;<br/>(ii) contains 18 neutrons?;<br/>(iii) is chemically unreactive?;<br/>(iv) readily forms an ion with two positive charges?<br/>(v) attain an octet structure by accepting one electron?;<br/>(vi) forms ionic bond with R?;<br/>(vii) belongs to the s-block in the Periodic Table?<br/> <br/>(c) Describe in outline how each of the following conversions can be carried out in the laboratory. Write appropriate equations for the reactions involved in each case<br/>(i) CuCO\(_3\) to Cu<br/>(ii) MgO to MgSO\(_4\).

a)(i) State Graham's law of diffusion.<br/>(ii) Calculate the vapour density of a triatomic gas X if its relative: atomic mass is 16.<br/>(iii) Equal volumes of gases Y and Z are maintained at the same temperature and pressure. If the mass of a molecule of Y is twice that of Z state and explain which of the molecules has the, greater average velocity.<br/> <br/>(b) The graph below is the ratio curve for the following reaction carried out in an open vessel.<br/>MgCO\(_{3(s)}\) + 2HCI\(_{(aq)}\) \(\to\) MgCl\(_{2(aq)}\) + CO\(_{2(g)}\) + H\(_2\)\(_{(l)}\).<br/><br/> <br/>(i) For how long did reaction occur?<br/>(ii) Why was there a loss in mass?<br/>(iii) State whether reaction rate was fastest at the beginning, the middle or towards the end of the reaction. Give reason for our answer.<br/>(iv) List three reaction conditions that can affect the slope of the curve<br/> <br/>(c) Consider the following reaction at equilibrium: PCI\(_{5(g)}\) \(\rightleftharpoons\) PCI\(_{3(g)}\)); \(\Delta\)H = +95 kJmol\(^{-}\)<br/>(i) Write an expression for the equilibrium constant K.<br/>(ii) Predict the effect of the following on the equilibrium position.<br/>I. Increased pressure<br/>II. Increased temperature<br/>III. Removal of chlorine Sketch an energy profile diagram for the forward reaction.

(a)(i) List two properties of iron that are characteristic of transition metals<br/>(ii) Using equations only, show the processes involved in the extraction of iron and the removal of impurities in the blast furnace.<br/>(iii) The following reaction occurs when a piece of iron is exposed to moist air for some days:<br/>4Fe\(_{(s)}\) + 3O\(_{2(g)}\) + xH\(_2\)O\(_{(l)}\) –> 2Fe\(_2\)O\(_3\)\(_{(s)}\) State three methods by which this reaction can be prevented<br/>(iv) What is the oxidation number of iiron in the product in (iii) above?<br/> <br/>(b)(i) Arrange the following metals in the order of increasing reactivity. Hence, state which of them is/are extracted by electrolysis Au, Zn, Mg, Na, Sn, Ca<br/>(ii) Why is zinc said to be amphoteric?<br/> <br/>(c)(i) Define oxidation in term of electron transfer<br/>(ii) Determine how many moles of electrons are transferred when 4825 coulombs of electricity are passed through an electrolytic cell. [1F = 96500C]<br/>(iii) Calculate the number of copper (II) ions that will be discharged by 0.250F. [Avogadro constant = 5.02 x 10\(^{23}\)

(a) What is meant by each of the following terms?:<br/>(i) Esterification<br/>(ii) Saponification<br/> <br/>(b)(i) Give the general moluecular 1 formula of alkynes<br/>(ii) Write the molecular formula and empirical formula of ethylethanoate.<br/>(iii) Draw the structure of 1, 1, 2, 2-tetrabromoethane<br/>(iv) Write an equation for the reaction of ethanol with sodium<br/> <br/>(c) Consider the following reaction schemes:<br/> I II<br/>Petroleum ---> Petroleum Fractions. Higher Petroleum Fractions ---> Petrol + X<br/><br/><br/>(i) State type of process/reaction involved in each of the stages labelled I to IV.<br/>(ii) Identify X and Y<br/>(iii) Give the IUPAC name of the product obtained in stage III.<br/>(iv) What are the reaction conditions for stage IV?<br/> <br/>(d) Explain why palm wine: (i) froths or foams (ii) tastes sour after some days.

(a)(i) Give the names of two allotropes of sulphur.<br/>(ii) State and explain what is observed when hydrogen sulphide is bubbled through acidified potassium tetraoxomanganatc (VII) solution<br/>(iii) List one product of the reaction of sulphur (IV) oxide with hydrogen sulphide<br/> <br/>(b)(i) What are the raw materials for the manufacture of tetraoxosulphate (VI) acid by the contact process?<br/>(ii) Write an equation for the reaction that requires a catalyst in the contact process and state the catalyst used.<br/>(iii) State the observation and the product formed when concentrated H\(_2\)SO\(_4\) reacts with each of the following:<br/>I. Copper turnings Ii. A cube of sugar<br/> <br/>(c)(i) Give three uses of sodium trioxocarbonate (IV).<br/>(ii) What name is given to reactions of the following type?: <br/> exposure to air<br/>Na\(_2\)CO\(_3\) + 10H\(_2\)O\(_{(s)}\) \(\to\) Na\(_2\)CO\(_3\); H\(_2\)O\(_{(S)}\) + 9H\(_2\)O<br/>(iii) Calculate the solubility of Na\(_2\)CO\(_3\) at 25°C, if 2.0 cm\(^3\) of its saturated solution at that temperature gave 1.75g of the anhydrous alt. [C = 12, O = 16, Na = 23].