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WAEC Physics 2013 Paper

Question : 17

Total: 46

Solution:

Concept:

The combined gas law relates pressure, volume, and temperature for a fixed mass of gas.

Explanation:

At initial conditions,

P_1 = 800\ \mathrm{mmHg}

V_1 = 76\ \mathrm{cm}^3

, and

T_1 = 27^\circ\mathrm{C} = 300\ \mathrm{K}

At standard temperature and pressure (s.t.p),

P_2 = 760\ \mathrm{mmHg}

and

T_2 = 273\ \mathrm{K}

Using the combined gas law:

V_2 = \frac{P_1V_1T_2}{P_2T_1}

Substitute the values:

V_2 = \frac{800 \times 76 \times 273}{760 \times 300}

Simplify step by step:

\frac{800}{760} = \frac{20}{19}

Then

V_2 = 76 \times \frac{20}{19} \times \frac{273}{300} = 80 \times 0.91

Therefore,

V_2 = 72.8\ \mathrm{cm}^3

Answer:

The volume at s.t.p is

72.8\ \mathrm{cm}^3

Correct option: B. $72.8\ \mathrm{cm}^3$ .

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