WAEC Chemistry Past Questions & Answers - Page 43

211.

Which of the following pairs of substances has the highest heat of neutralization?

A.

strong acid and strong base

B.

weak acid and weak base

C.

strong acid and weak base

D.

weak acid and strong base

Correct answer is A

In other terms, the stronger the acid the greater the amount of hydrogen ions present in the solution, and hence the more alkali that should be required to neutralise the solution, hence increasing the enthalpy

212.

Consider the following reaction equation: 2Al(OH)\(_3\) + 3H\(_2\)SO\(_4\) Al\(_2\)(SO4)\(_3\)(aq)+6H\(_2\)O. How many moles of tetraoxosulphate(vi)acid is needed to produce 0.5mol of aluminium tetraoxosulphate(vi)?

A.

0.5

B.

1.0

C.

1.5

D.

3.0

Correct answer is C

Where 3mols of H2So4 = 1 mol of (Al2SO4)3
y mols of H2SO4 = 0.5 mol of (Al2SO4)3
Then cross multiply to have:
y = \(\frac{3×0.5}{1}\)
y = 1.5 moles

213.

The most suitable indicator for the reaction between NaOH and HCOOH is?

A.

bromocresol

B.

methyl orange

C.

methyl red

D.

phenolphthalein

Correct answer is D

Phenolphthalein is suitable as indicator for this reaction i.e strong base and weak acid

214.

A sample of air was bubbled into water. The PH of the water slowly changed from 7 to 6. Which of the following gases in the samples caused the change?

A.

carbon(iv)oxide

B.

carbon(ii)oxide

C.

nitrogen

D.

oxygen

Correct answer is A

An acid gas is any gaseous compound which, when dissolved in water, will form an acidic solution

The most common acid gases are hydrogen sulfide (H2S) and carbon dioxide (CO2) gases

215.

Which of the following solutions containing one mole per dm\(^3\) of the compound would have the lowest PH?

A.

ethanoic acid

B.

hydrochloric acid

C.

sodium chloride

D.

sodium hydrogentrioxocarbonate(iv)

Correct answer is B

Low PH means strongly acidic cause acidity increases with decreasing PH values.

Example is Hydrochloric Acid