Post Utme Ahmadu Bello University Chemistry Past Questions and Answers

Question 16:

When carbon dioxide is bubbled into limewater, a white precipitate is formed. If the passage of the gas is continued,the precipitate disappears.
The reasons for this is ____________

A. Calcium carbonate is formed which on reaction dissolves
B. Calcium hydrogen carbonate is precipitated and then dissolves
C. Calcium carbonate is formed which on reaction with further carbon dioxide forms soluble calcium hydrogen carbonate
D. Concentration of solution has occurred with the deposition of calcium hydroxide
E. The solution has become saturated and solid carbon dioxide has been deposited

Question 17:

The following reactions are stages in important industrial processes
(i) \(\mathrm{N}_{2(9)}+\mathrm{O}_{2}-2 \mathrm{NH}_{3(9)} \Delta \mathrm{H}\) is negative
(ii) \(2 \mathrm{SO}_{2(g)}+\mathrm{O}_{2(g)}-2 \mathrm{SO}_{3(g)} \Delta \mathrm{H}\) is negative
(iii) \(\mathrm{N}_{2(g)}+\mathrm{O}_{3(9)}-2 \mathrm{NO}_{(9)} \Delta \mathrm{H}\) is positive.
Which of the above forward reactions is favoured by a decrease in the concentration of the pressure and an increase in temperature?

A. I
B. Ii
C. Iii
D. I & ii
E. I & iii

Question 18:

Methanoic acid mixes with water in all proportions and has about the same boiling point as water. Which of the following methods would you adopt to obtain pure water from a mixture of sand, water and methanoic acid

A. Fractional distillation
B. Filtration followed by aestivation
C. Neutralities with sodium hydroxide followed by distillation.
D. Neutralization with sodium hydroxide followed by filtration
E. Etherification with ethanol followed by distillation

Question 19:

Which of the following statements applies during theelectrolysis of sodium hydroxide solution using platinum electrodes?

A. Anions are discharge at the cathode
B. Hydrogen ions are discharge at the anode
C. The concentration of sodium hydroxide decreases at both electrode compartments
D. The concentration of sodium hydroxide increases at the cathode only
E. The concentration of sodium hydroxide increases at the anode only

Question 20:

Which of the following statement is true When the potassium atom forms its ion?

A. It gains one electron and becomes neutral
B. Its atomic number decreases
C. It achieves electronic configuration of argon
D. It loses one proton
E. It loses one neutron.