Chemistry 1997 Waec Past Questions and Answers

Question 61 :

• WAEC 1997

(a)(i) State two general methods of preparing soluble salts.
(ii) Mention three pieces of apparatus required for determining the solubility of a salt at a given temperature.

(b) The solubilities of two salts represented as K and L were determined at various temperatures. The results are shown in the table below:

Temperature (\(^o\)C)	0	20	40	60	80	90
Solubility of K (mol. dm\(^{-3}\))	0.38	0.46	0.54	0.62	0.69	0.73
Solubility of L (mol. dm\(^{-3}\))	0.12	0.34	0.64	1.08	1.64	2.00

(i) Plot the solubility curves of K and L on the same graph. Use the curves to answer questions (ii) - (iv) below.
(ii) What is the solubility of K at 50°C?
(iii) At what temperature is the solubility of L equal to 1.0mol. dm\(^{-3}\)?
(iv) Over what temperature range is K more soluble that L?
(v) Given that the molar mass of L is 101g, determine whether a solution containing 3.4g of L per 250cm\(^3\) at 20°C is saturated or unsaturated.

Question 62 :

• WAEC 1997

(a)(i) What is meant by cracking of petroleum fractions?
(ii) Write an equation for the laboratory preparation of ethene from ethanol.
(iii) Give one chemical test to distinguish between ethane and ethene.

(b)(i) Name the class of carbohydrates to which starch and cellulose belong.
(ii) What process is used for isolating ethanol from the other products of fermentation of sugar?
(iii) Name the organic product of the reaction between ethanol and sodium
(iv). Write the structural formula of 2-chloroethanol.

(c) State the reason why:
(i) benzene produces more soot than ethene on burning in excess air;
(ii) ethanoic acid has a higher boiling point than methanoic acid;
(iii) sodium chloride is used during the manufacture of soap.
(d) Give one use of: (i) ethyne (ii) coal (iii) carbon black