Question

If 10⁻⁴ dm³ of water is introduced into a 1 dm³ flask at 300 K, how many moles of water are in the vapour phase when equilibrium is established?

(Given: Vapour pressure of H₂O at 300 K is 3170 Pa; R = 8.314 JK⁻¹ mol⁻¹)

Options

• 5.56 × 10⁻³ mol

• 1.53 × 10⁻² mol

• 4.46 × 10⁻² mol

• 1.27 × 10⁻³ mol

Answer 1

1.27 × 10⁻³ mol

Explanation:

The value of volume used should be the volume of the container (1 dm³) as the number of moles of water in the vapour phase is to be calculated and the volume of water is negligibly small (10⁻⁴ dm³).

pV = nRT  .....(1 dm³ = 10⁻³ m³)

n = `(3170 xx 1 xx 10^-3)/(8.314 xx 300)`

= 1.27 × 10⁻³ mol