WAEC Chemistry Past Questions & Answers - Page 219

1,091.

30cm3 pf hydrogen at s.t.p combine with 20cm3 of oxygen to form steam according to the following equation 2H2(g) + O2(g) → 2H2O(g).

Calculate the total volume of the gaseous mixture at the end of the reaction

A.

50cm3

B.

35cm3

C.

30cm3

D.

25cm3

Correct answer is B

2H\(_2\)(g) + O\(_2\)(g) → 2H\(_2\)O(g).


2 volumes of H\(_2\)(g) and 1 volume of O\(_2\)(g) produced 2 volumes of H\(_2\)O\(_2\)

ratio of reacting volumes

30cm\(^3\) + 15cm\(^3\) → 30cm\(^3\)

30cm\(^3\) of Hydrogen requires 15cm\(^3\) of oxygen to produce 30cm\(^3\) of water.

Excess oxygen: 20cm\(^3\) – 15cm\(^3\) = 5cm\(^3\)

Total volume of gaseous mixture: 5cm\(^3\) of Oxygen + 30cm\(^3\) of Water = 35cm\(^3\)

1,092.

Helium is preferred to hydrogen in filling balloons because hydrogen

A.

is inflammable

B.

is diatomic

C.

exhibits isotopy

D.

is a component of water

Correct answer is A

Helium is a colorless, non-toxic, non-flammable gas that is lighter than air. When balloons are filled with helium, they will float.

1,093.

What volume of hydrogen is produced at s.t.p. When 2.60 g of zinc reacts with excess HCI according to the following equation? Zn(s) + 2HCI(aq) → ZnCI 2(aq) + H2(g) [Zn = 65; 1 mole of a gas occupies 22.4dm3 at s.t.p]

A.

0.040dm 3

B.

0.896dm 3

C.

5.82dm 3

D.

8.62dm 3

Correct answer is B

Zn + 2HCI → ZnCI2 + H2; 65g of Zn produces 22.4 dm3 of H2; .: 2.6g of Zn will produce = 2.6/65 x 22.4 = 0.896 dm3

1,094.

Gas molecules are said to be perfectly elastic because

A.

they collide without loss of energy

B.

they move about in straight lines

C.

the distances between them are negligible

D.

the volume occupied by them is negligible

Correct answer is A

No explanation has been provided for this answer.

1,095.

Equal volumes of CO2 cnd CO at s.t.p have the same

A.

mass

B.

density

C.

rate of diffusion

D.

number of molecules

Correct answer is D

No explanation has been provided for this answer.