# Chemistry

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The vapor pressures of ethanol (C2H5OH) and 1-propanol (C3H7OH) are 100 mmHg and 37.6 mmHg, respectively. Assume ideal behavior and calculate the partial pressures of ethanol and 1-propanol at 35 degrees Celsius over a solution of ethanol in 1-propanol, in which the mole fraction of ethanol is .300 .

I used the equation Pi = Xi * Ptotal. Where Pi is the partial pressure and Xi is the mole fraction.

So for ethanol I got Pi = .3 * 100mmHg = 30 mmHg (correct answer)

However for 1-propanol:
Pi = .3 * 37.6mmHg = 11.28 mmHg

But the book is telling me the answer is 26.3 mmHg.

• Chemistry -

And the book is right.
If the mole fraction for ethanol is 0.3, then the mole fraction for 1-propanol is 0.7 since mole fractions must add to 1.00.

• Chemistry -

THE MOLE FRACTION OF THE SOLUTES YIELD AT 1. THEREFORE IF ETHANOL HAS THE MOLE FRACTION OF 0.300, THE MOLE FRACTION OF 1-PROPANOL SHOULD BE 0.700 THEN USE THE EQUETION:Pi=Xi*P
=0.700*37.6mmHg
=26.32mmHg

• Chemistry -

26.32