Question

4.(b)(i) State Dalton's law of partial pressures.
(ii) The volume of a sample of methane collected over water at a temperature of 12°C was 30cm³ when the pressure of the dry gas at s.t.p was measured with saturated vapour pressure of water at 12°C being 10mmHg and real pressure 700mmHg. Calculate the volume of the dry gas at s.t.p.

Accepted Answer

(i) Dalton's law of partial pressures states that in a mixture of gases which do not react chemically, the total pressure exerted by the mixture is the sum of the partial pressures exerted by the individual gases.
(ii) Real pressure of gas at 12°C = 700−10 = 690mmHg. Using P₁V₁/T₁ = P₂V₂/T₂ with T₁=285K, T₂=273K, P₂=760mmHg, V₁=30cm³: V₂ = (690×30×273)/(760×285) ≈ 26.09cm³.

WAEC Chemistry 2018 Theory — Question 20

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