Chemistry 1994 Waec Past Questions and Answers

Question 46 :

• WAEC 1994

(a) State whether entropy increases or decreases during each of the following processes
(i) condensation of steam;
(ii) melting of wax;
(iii) dissolution of sugar in water;
(iv) abscas on charcoal.

(b) What deduction can be made in each case given that the value of the free energy change for a particular reaction is:
(i) zero;
ii) negative

Question 47 :

• WAEC 1994

Potassium trioxochlorate (V) undergoes thermal decomposition according to the fotpowing equation: 2KCIO\(_3\) \(\to\) 2KCI + 3O\(_2\)
(a) What substance could be used in the laboratory to in ease the rate of the reaction
(ii) absorb the oxygen produced
(b) Give the reason why an aqueous solution of silver trioxonitrate (V) gives a white precipitate with KCI but not with KClO\(_3\).

Question 48 :

• WAEC 1994

(a)(i) Draw a labelled diagram for the laboratory preparation of a dry sample of chlorine
(ii) Give one chemical test for chlorine.

(b) Write equations to represent the reaction of chlorine gas with: (i) iron (II) chloride solution;
(ii) potassium iodide solution;
(iii) hot concentrated sodium hydroxide solution.

(c) State what is observed on:
(i) bubbling hydrogen chloride gas into an solution of lead (II) trioxonitrate (V);
(ii) heating the mixture from (c)(i) above to boiling and aging it to cool.
(d) A solution of bismuth chloride was prepared by adding the oxychloride which is a white powder to concentrated hydrochloric acid. The following equilibrium was set up: BiOCI\(_{(s)}\) + 2HCI\(_{(aq)}\) \(\rightleftharpoons\) BiCl\(_{3(aq)}\) + H\(_2\)O\(_{(q)}\). State what would be observed if some water is added to the system. Explain your answer

Question 49 :

• WAEC 1994

(a)(i) What is meant by hydrocarbons?
(ii) A hydrocarbon consists of 92.3% carbon. If it's vapour density is 39, determine its molecular formula. (H = 1; C = 12)

(b)(i) Outline a suitable laboratory procedure for obtaining ethanol from cassava tubers
(ii) List two laboratory reagents used for oxidizing ethanol to ethanoic acid.

(c) What name is given to each of the following processes?:
(i) Conversion of alkanols to alkanoates;
(ii) Breakdown of proteins to amino acids;
(iii) Conversion of oils to fats
(iv) Alkaline hydrolysis of fats and oils.

Question 50 :

• WAEC 1994

(a)(i) Determine the maximum number of electrons that can occupy the principal energy level M of an atom.
(ii) Show the changes in the electronic structures of atoms of sodium and fluorine (\(^{23}_{11}\)Na: \(^{19}_{9}F\)) when they combine to form sodium fluoride.
(iii) State: three properties that sodium fluoride would have, based a-n the bond type present in the compound.

(b) Write equations to show when:
(i) sodium metal burns in limited supply of oxygen;
(ii) water is added to the product in (b)(i) above

(c) Describe a suitable laboratory procedure for comparing the conductance of 1 mol dm\(^{-3}\) aqueous solutions of sodium hydroxide and ethanoic acid.