WAEC Chemistry Past Questions & Answers - Page 101

501.

A major factor considered in selecting a suitable method for preparing a simple salt is its

A.

crystalline form

B.

melting point

C.

reactivity with dilute acids

D.

solubility in water

Correct answer is D

No explanation has been provided for this answer.

502.

The gas given off when NH4 Cl is heated with an alkali is

A.

H2

B.

Cl2

C.

N2

D.

NH3

Correct answer is D

No explanation has been provided for this answer.

503.

Determine the mass of sulphur (IV) oxide obtained when 91.0g of oxygen reacts completely with sulphur according to the following equation: S(s) + O\(_2\)(g) → SO\(_2\)(g) [S = 32; O = 16]

A.

123g

B.

139g

C.

155g

D.

182g

Correct answer is D

S + O\(_2\) → SO\(_2\).

According to the equation 32g of O\(_2\) produced 64g of SO\(_2\)

therefore 91g of O2 will produce yg of SO2
y = \(\frac{91 * 64}{32}\)

y = 182g of SO\(_2\)

504.

Calculate the mass of chlorine gas which occupies a volume of 1.12 dm\(^3\) a volume of 1.12 dm\(^3\) at s.t.p [Cl = 35.5, 1 mole og gas occupies 22.4 dm\(^3\) at s. t. p ]

A.

1.80g

B.

3.55g

C.

7.10g

D.

15.50g

Correct answer is B

1 mole Cl\(_2\) occupy 22.4dm\(^3\)
i.e 2 x 35.5 → 22.4 ; x → 1. 12
:. x = \(\frac{1.12}{22.4}\) x 2 x 35.5 = 3.55

505.

What volume of hydrogen will be produced if 100cm3 of ammonia is completely decomposed at constant temperature and pressure? The equation for reaction is 2NH3(g) → N2(g) + 3H2(g)

A.

50cm3

B.

150cm3

C.

200cm3

D.

300cm3

Correct answer is B

According to the equation 2NH3 → N3 + 3H2
2 x 22400cm3 of ammonia will produce
3 x 22400cm3 of hydrogen
If 100cm3 of NH3 is used.
:. H2 volume = \(\frac{100}{2x22400} x 3x22400
=150cm3