Calculate the mass of a non-volatile solute (molar mass 40 g mol-1
) which should be dissolved in
114 g octane to reduce its vapour pressure to 80%
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Answer:
Let p be the vapour pressure of pure octane. The vapour pressure of solution will be
100
80
p=0.8 p.
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÷Mw
p-0.8p÷p=W×114÷40×114
W=8g
Hence, 8 g of solute are required.
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