Waec Chemistry 1993 Past Questions and Answers

Question 36:

• WAEC 1993

(a) Give one disadvantage of:
(i) hard water
(ii) soft water
(b) Explain why the degree of hardness in a sample of clear lime water is higher than in another sample has that been turned milky by carbon (IV) oxide.

Question 37:

• WAEC 1993

(a) State one air pollution that causes:
(i) blood poisoning
(ii) acid poisoning
(iii) blackening of the walls of buildings

(b) Mention one major chemical industry in each case which requires the following as raw materials:
(i) petrochemicals;
(ii) cellulose.

Question 38:

• WAEC 1993

(a) If L is the Avogadro constant and E° is standard cell potential, state what X and Y stand for in the following expressions
(i) X = \(\frac{\text{Mass of L molecules of gas or vapour}}{\text{ Mass of L molecules of hydrogen}}\)
(ii) Y = -nFE°
(b) State two differences between a primary cell and a secondary cell.

Question 39:

• WAEC 1993

(a) State the phenomenon illustrated by the:
(i) spreading of the smell of hydrogen sulphide gas in the laboratory;
(ii) existence of atoms of the same element having different mass numbers
(b) The atomic number of an element is 17. It has different atoms containing 18 neutrons and 20 neutrons, with a relative abundance of 75% and 25% respectively. Calculate the relative atomic mass of the element.

Question 40:

• WAEC 1993

(a) Name the residue obtained on strongly heating the following:
(i) ZnCO\(_3\) in an open crucible;
(ii) CuSO\(_4\), 5H\(_2\)O and then allowing it to cool in a desiccator.
(b) State the colour changes observed on heating and cooling in each case in(a) above.