Question

* 2.18 Calculate the mass of a non-volatile solute (molar mass 40 g mol") which
should be dissolved in 114 g octane to reduce its vapour pressure to 80%.

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Answer 1

Explanation:

Let p be the vapour pressure of pure octane. The vapour pressure of solution will be

80/100p=0.8p

Molar mass of solute (M) and octane (m) are 40 g/mol and 114 g/mol respectively. Mass of octane, w is 114 g.

p−p'/p=Wm/Me

p-0.8p/p=W*114/40*114

W=8gm

Hence, 8 g of solute are required