JAMB Past Questions and Answers - Page 1544

7,716.

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

A.

Na+ ions are discharged at the cathode

B.

Hydrogen ions are discharged at the cathode

C.

the concentration of sodium hydroxide decrease 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

Correct answer is B

Electrolysis of conc NaOH using platinum elcetrodes:

At the cathode, Hydrogen gas is evolved

at the anode, Oxygen gas is evolved.

7,717.

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 stand, water and methanoic acid?

A.

fractional distillation

B.

filtration followed by distillation

C.

neutralization with sodium hydroxide followed by distillation

D.

esterification with ethanol followed by distillation

E.

neutralization with sodium hydroxide followed by filtration

Correct answer is E

Water added to an acid decreases its pH, hence, methanoic acid and water (azeotropes with very close boiling points) will be more acidic. Hence, addition of sodium hydroxide forms a salt and water. Then filtration can be done easily.

7,718.

When carbondioxide is bubbled into limewater a white precipitate is formed. If the passage of the gas is continued, the precipitate disappears. The reason 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 carbondioxide forms solube calcium hydrogen carbonate

D.

concentration of the solution has occurred with the deposition of calcium hydroxide

E.

the solution has become saturated and solid carbondioxide has been deposited

Correct answer is C

No explanation has been provided for this answer.

7,719.

The oxidation state of manganese in potassium permanganate is

A.

+7

B.

+5

C.

+3

D.

+2

E.

+1

Correct answer is A

No explanation has been provided for this answer.

7,720.

The reaction of zinc with copper (ll) ions in aqueous solution can be represented as follows: Cu 2+(aq) +Zn (s) → Cu(s) + Zn 2+(aq).Which of the following is the most complete description of this reaction?

A.

Copper (ll) ions are being reduced

B.

Zinc is being oxidized.

C.

Copper (ll) ions and zinc are being reduced

D.

copper (ll) ions and zinc are being oxidized

E.

copper(ll) ions are being reduced and zinc oxidized

Correct answer is E

No explanation has been provided for this answer.