Chemistry questions and answers

Chemistry Questions and Answers

Learn more about the properties, composition, and structure of substances (elements and compounds) with these Chemistry questions and answers. This Test can be used by students preparing for Chemistry in JAMB, WAEC, NECO or Post UTME.

646.

Which of these sources of water may likely contain the least concentration of Ca\(^{2+}\) and Mg\(^{2+}\)?

A.

Spring water

B.

River water

C.

Tap water

D.

Sea water

Correct answer is C

Tap water contains less Ca\(^{2+}\) and Mg\(^{2+}\)

647.

Aluminium does not react with either dilute or concentrated trioxonitrate (V) acid because

A.

it is insoluble in either dilute or concentrated trioxonitrate (V) acid

B.

it is lower than hydrogen in the electrochemical series

C.

the reaction with trioxonitrate (V) acid has a light activation energy

D.

an insoluble oxide is formed on its surface which renders it passive

Correct answer is D

Aluminium doesn’t react with either dilute or concentrated trioxonitrate (V) acid because an insoluble oxide is formed on its surface which renders it passive. It will depend on the concentration of the nitric acid used…. Although aluminium reacts with dilute nitric acid to produce aluminium nitrate and hydrogen gas, concentrated (>60%) nitric acid is such a powerful oxidising agent that it instantly causes a thin layer of aluminium oxide to coat the surface of the aluminium

648.

The presence of ammonia gas in a desiccator can exclusively be removed by

A.

phosphorus (V) oxide

B.

fused calcium chloride

C.

calcium oxide

D.

concentrated tetraoxosulphate (VI) acid

Correct answer is D

Ammonia gas can be removed from a dessicator by adding a conc. H2SO4 so as to neutralize it since ammonia gas is basic.

649.

The collision theory explains reaction rates in terms of

A.

size of the product

B.

frequency of collision of the reactants

C.

size of reactant

D.

frequency of collision of the products

Correct answer is B

Collision theory is the theory used to predict the rates of chemical reactions, particularly for gases. The collision theory is based on the assumption that for a reaction to occur it is necessary for the reacting species (atoms or molecules) to come together or collide with one another.

650.

The end products of burning a candle in the atmosphere are water and 

A.

carbon (II) oxide

B.

sulphur (IV) oxide

C.

carbon (IV) oxide

D.

sulphur (VI) oxide

Correct answer is C

When we ignite a candle, the hydrocarbon reacts with oxygen (in excess) to produce carbon dioxide and water. The burning sets an air current which gives dome shape to candle flame and it helps to get complete combustion at the bottom and the outer surface of the flame.

CO\(_2\) is produced