Heptane and octane form ideal solution. At 373 K, the vapour pressures of the pure liquids are 106 k — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

Molar mass of heptane ($\text{C}_7\text{H}_{16}$) = 100 g/mol; moles = $30.0 / 100 = 0.3 \text{ mol}$. Molar mass of octane ($\text{C}_8\text{H}_{18}$) = 114 g/mol; moles = $34.2 / 114 = 0.3 \text{ mol}$. Mole fractions: $X_H = 0.5$, $X_O = 0.5$. Total pressure $P = 106(0.5) + 46(0.5) = 53 + 23 = 76 \text{ kPa}$. Converting to bar: $76 \text{ kPa} = 0.76 \text{ bar}$ ($1 \text{ bar} = 100 \text{ kPa}$). Therefore, correct answer is D.