Chemistry 1989 Waec Past Questions and Answers

Question 16 :

• WAEC 1989

Copper can best be purified by

A. Roasting the impure copper in a blast furnace
B. Heating the oxide with coke
C. Electrolyzing a copper (ll) salt solution using the impure copper as the anode
D. Converting the impure copper to a trioxonitrate (V)
E. Washing the impure copper with sodium hydroxide solution

Question 17 :

• WAEC 1989

Locally produced soap in which wood ash is used as the base is usually soft because the wood ash contains a lot of

A. Sodium ions
B. Potassium ions
C. Lithium ions
D. Calcium ions
E. Magnesium ions

Question 18 :

• WAEC 1989

Why is potassium fluoride added to the electrolyte in the extraction of sodium from fused sodium chloride?

A. Pure sodium chloride does not conduct electricity
B. Potassium fluoride prevents the sodium produced from attacking the electrodes
C. Potassium fluride increases conductivity
D. Potassium fluride reduces the temperature at which sodium chloride fuses
E. The potassium fluride acts as a catalyst

Question 19 :

• WAEC 1989

The rate of the hydrogen in the reaction Zn_(s) + 2HCI _(aq) → ZnCI _2(g) + H _2(aq) + H _2(g) can be increased by

A. Using Zinc powder instead of Zinc granules
B. Using dilute instead of concentrated hydrochloric acid
C. Cooling the container in which the mixture is placed
D. Using an alloy of zinc instead of pure zinc
E. Using hydrogen chloride gas instead of hydrochloric acid solution

Question 20 :

• WAEC 1989

Octane number is highest in petrol containing a high proportion of

A. Heptane
B. Octane
C. 2-methylpentane
D. 2, 4-dimethylpentane
E. 2,2,4-trimethylpentane