Waec Chemistry 1999 Past Questions and Answers

Question 46:

• WAEC 1999

(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?
(i) Addition reaction;
(ii) Combustion;
(iii) Substitution reaction.

(b)(i) Name the process by which an alkanol can be converted to an alkene.
(ii) Write the name and structural formula of the third member cf the alkanol series.
(iii) State what would be obtained if a primary alkanol reacted with excess acidified KMnO\(_4\) solution.

(c)(i) Give one chemical test for alkanoic acids.
(ii) Write an equation to show how methanoic acid reacts with ethanol in the presence of mineral acids.
(iii) What is the role of mineral acid in the reaction in (c) ii?

(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.
(i) Identify H
(ii) State the class of carbohydrates to which starch belongs and explain what happened to the starch during treatment with malt.
(iii) Draw a labelled diagram of a suitable set-up for obtaining a sample of J from the reaction mixture.

Question 47:

• WAEC 1999

(a)(i) Give two differences between a conductor and an electrolyte.
(ii) State three applications of electrolysis.
(iii) Write equation for the reaction at each electrode when a dilute solution of sodium chloride is electrolysed using carbon electrodes.
(b)(i) What is an electrochemical cell?
(ii) Give two examples of primary cells.
(iii) Split the following equation into two balanced hall cell equations. Mte + Fe\(^{2+} \to Mg^{2+} + Fe\).
(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
(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?
(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]
(ii) What type of reaction was involved in (d)(i)?

Question 48:

• WAEC 1999

(a)(i) Define allotropy.
(ii) Name the allotrope of carbon used in gas masks.
(iii) Mention two other elements which exhibit allotropy apart from carbon.

(b) List the products of each of the following reactions:
(i) Heating coal in the absence of air.
(ii) Burning of candle wax in plentiful supply of air

(c)(i) State the two properties of carbon (IV) oxide which make it useful in extinguishing fire.
(ii) Write an equation for the reaction of carbon (IV) oxide with lime water
(iii) Calculate the volume of oxygen that was in excess if 150cm\(^3\) of carbon (II) oxide was burnt in 80cm\(^3\) of oxygen according to the following equation: 2CO\(_{(g)}\) + O\(_{2(g)}\) \(\to\) 2CO\(_{2(g)}\).

(d)(i) State how nitrogen can be obtained from ammonia gas.
(ii) Name the gaseous fuels obtained when steam and air are passed over red hot coke.
(iii) Which of the fuels in (d)(ii) has the lower heating ability? Give reason for your answer.