Chemistry questions and answers

Chemistry Questions and Answers

Learn more about the properties, composition, and structure of substances (elements and compounds) with these Chemistry questions and answers. This Test can be used by students preparing for Chemistry in JAMB, WAEC, NECO or Post UTME.

2,852.

30cm3 of hydrogen was collected over water at 27°C and 780 mm Hg. If the vapour pressure of water at the temperature of the experiment was 10 mm Hg, calculate the volume of the gas at 760 mm Hg and 7°C?

A.

40.0 cm3

B.

35.7 cm3

C.

28.4 cm3

D.

25.2 cm3

Correct answer is C

Y1 = 30cm3 T1 = 27 + 273 = 300K and P1 = (780 - 10)mm Hg i.e the pressure minus the vapour pressure of water
P2 = 760mm Hg and T2 = 7 + 273 = 280K
From (P2V2) / (T2) = (P1V1) / (T1)
(770 x 30) / (300) = (760 x O2) / (280)
V2 = (770 x 30x 280) / (300 x 760)
V2 = 28.4 cm3

2,853.

C3H8(g) + 502(g) → 4H2O + 3CO2(g). Form the equation above the volume of oxygen at s.t.p. required to burn 50cm3 of propane is?

A.

250 cm3

B.

150 cm3

C.

100 cm 3

D.

50 cm3

Correct answer is A

C3H8 + 502 → 4H2O + 3CO2.
From the equation above 1 dm3 of C3H8 require 5dm3 of O2 at s.t.p.
∴ 50cm3 of C3H8 require x = (50) / (1000) x 5 x 1
x = (250) / (1000)
x = 250cm

2,854.

8.0 g of an element X react with an excess of copper (ll) tetraoxosulphate (lV) solution to deposit 21.3 g of copper. The correct equation for the reaction is?

(Cu = 64).

A.

X(s) + CuSO4(aq) → Cu(s) + XSO4(aq)

B.

X(s) + 2CuSO4(aq) → 2Cu(s) + X(SO4)2(aq)

C.

2X(s) + CuSO4(aq) → Cu(s) + X2SO4(aq)

D.

2X(s) + 3CuSO4(aq) → 3Cu(s) + X2(SO4)3(aq)

Correct answer is A

No explanation has been provided for this answer.

2,855.

A given amount of gas occupies 10.0 dm3 at 4atm and 273°C. The number of moles of the gas present is?
(Molar volume of a gas at s.t.p. = 22.4 dm3)

A.

0.89 mol

B.

1.90 mol

C.

3.80 mol

D.

5.70 mol

Correct answer is A

\(V_1\) = \(10dm^3\), \(V_2\) = ?, \(P_1\) = 4atm =  4 x 760 = 3040mmHg, \(P_2\) = 760mmHg \(T_1\) = 273ºc = 273 + 273 = 546K, \(T_2\) = 273K

Using the general gas law = \(\frac{P_1 V_1}{ T_1} = \frac{P_2 V_2}{T_2}\)

\(V_2  = \frac{P_1 V_1 T_2}{P_2 T_1}\)

\(V_2 = \frac{ 3040 \times10 \times273}{760 \times546}\)

\(V_2 = 20dm^{-3}\)

1mole of a gas = \(22. 4dm^{3}\)

  x                     = \(20.0dm^{3}\)

= 0.89mol.