One mole of heptane (V.P. = ) is mixed with four moles of octane (V.P. = ) to form an ideal solution — Solutions and Colligative Properties Chemistry Question
Question
One mole of heptane (V.P. = $92\text{ mm Hg}$) is mixed with four moles of octane (V.P. = $31\text{ mm Hg}$) to form an ideal solution. Calculate the total vapour pressure of the resulting mixture.
Answer: C
💡 Solution & Explanation
Total moles $= 1 + 4 = 5$. Mole fraction of heptane $= 1/5$, octane $= 4/5$. By Raoult's law, $P_{total} = (92 \times \frac{1}{5}) + (31 \times \frac{4}{5}) = 18.4 + 24.8 = 43.2\text{ mm Hg}$.
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