WAEC Past Questions and Answers - Page 1414

7,066.

The mass of 800cm3 of gas Q at s.t.p. is 1.0g. What is the molar mass of Q? [Avogadros constant = 22.4dm3 mol-1`]

A.

18.0 gmol-1

B.

22,4gmol-1

C.

28.0gmol-1

D.

36.0 gmol-1

Correct answer is C

Imole Q occupies 22400 cm3
x mole occupies 800 cm3
x = \(\frac{800 x 1}{22400}\)
= 0.036mol

Molar mass = Mass ÷ Mole 

                    = 1 ÷ 0.036

 Molar mass ≈ 28 g/mol

7,067.

If 0.20 mol dm-3 NaOH(aq) was evaporated to yield 5.0g of solid NaOH, calculate the volume of NaOH (aq) used. (Na = 23.0,O = 16:0; H = 1.00)

A.

600cm-3

B.

625cm3

C.

10003

D.

1600 cm 3

Correct answer is B

Mole = 5/40 = 0.125 mole
:. 0.2 mole NaOH dissolved in 1000 cm3
0.125 mole NaOH dissolved in xcm3
xcm3 = \(\frac{0.215 x 1000}{0.2}\)
= 625cm3

7,068.

The oxidation number of sulphur in Fe2(SO4)3 is

A.

+2.

B.

+3

C.

+4.

D.

+6.

Correct answer is D

Fe2(SO4)3 = 0
(+3 x 2) 9 3x + (-2 x 4 x 3) = 0
+6 + 3x -24 = 0
+3x - 18 = 0
3 x = 18
x = 18/3 = +6

7,069.

A gaseous mixture contains 0,256 g of hydrogen and 2.00 g of oxygen. The mole ration of hydrogen to oxygen in the mixture is (H=1.00; O=16,0)

A.

1:1

B.

2:1

C.

1:4

D.

8:1

Correct answer is B

Mole = \(\frac{Mass}{Molar Mas}\) : \(\frac{Mass}{Molar Mass}\)
\(\frac{0.256}{2}\) : \(\frac{2}{32}
0. 128 : 0.0625
\(\frac{0.128}{0.0625}\) : \(\frac{0.0625}{0.0625}\)
2 : 1

7,070.

An aqueous solution of Na2CO3 is

A.

acidic

B.

alkaline

C.

amphoteric

D.

neutral

Correct answer is B

No explanation has been provided for this answer.