WAEC Past Questions and Answers - Page 1345

6,721.

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

6,722.

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

6,723.

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

6,724.

Vinegar is an aqueous solution of?

A.

Hydrochloric acid

B.

ethanedioc acid

C.

ethanoic acid

D.

hydrofluoric acid

Correct answer is C

Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings

6,725.

What is the solubility of a salt X at 25ºC if the saturated solution of the salt contains 0.28g in 100cm\(^3\) of the solution in mol\dm\(^3\)? 

[ X = 56.0g ]

A.

0.05

B.

0.10

C.

2.60

D.

2.80

Correct answer is A

(mass / molar mass) X (1000 / vol )

(0.28 / 56.0) X (1000 / 100 )

= 2.8 / 56 

= 0.05 mol\dm\(^3\)