Chemistry Past Questions and Answers

The alloy used for metal work and plumbing contains

Classify each of the following as physical change or a chemical change:
(a) fractional distillation of liquefied air;
(b) cracking of petroleum fractions;
(c) conversion of rhombic sulphur to monoclinic sulphur;
(d) chromatographic separation of chlorophyll.

(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.

(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.

(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.