WAEC Chemistry Past Questions & Answers - Page 134

666.

On evaporation to dryness, 250 cm3 of saturated solution of salt X with relative molar mass 101 gave 50.5g of the. What is the soluility of the salt?

A.

1.0 mol dm-3

B.

2.0 mol dm-3

C.

4.0 moldm-3

D.

5.0 moldm-3

Correct answer is B

50.5g 0f salt X is contained in 250cm3,

what mass of X is contained in 1000cm3 

= (50.5 x 1000) ÷ 250 = 202g

no of moles of salt x = mass÷ molar mass

= 202÷ 101 = 2.0mol/dm3

667.

Which of the following metallic oxides is amphoteric?

A.

AI2O3

B.

Fe2O3

C.

MgO

D.

Na2O

Correct answer is A

No explanation has been provided for this answer.

668.

When NH 4CI was dissolved in water, the container was cold to touch. This implies that

A.

the process is endothermic

B.

the process is exothermic

C.

NH4CI is highly soluble in water

D.

NH 4CI forms a saturated solution

Correct answer is A

No explanation has been provided for this answer.

669.

Which of the following statements about enthalpy of neutralization is correct? It

A.

is constant for a strong acid and a strong base

B.

cannot be determined using calorimeter

C.

has a positive value

D.

is higher for strong acid and a weak base

Correct answer is A

No explanation has been provided for this answer.

670.

The colour of phenolphthalein indicator in alkaline solution at the end-point of an acid-base titration is?

A.

colourless

B.

orange

C.

pink

D.

yellow

Correct answer is C

Phenolphthalein is one of the most commonly-used indicators in neutralisation titration.

Phenolphthalein is naturally colorless but turns pink in alkaline solutions.