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Question
Calculate the mole fraction of solute, if the vapour pressure of pure benzene at a certain temperature is 640 mmHg and the vapour pressure of a solution of a solute in benzene is 600 mmHg.
Solution
We can use Raoult's law to calculate the mole fraction of the solute. Raoult's law states:
Where:
- Psolution = 600 mmHg
- Ppure solvent = 640 mmHg
- Xsolvent = mole fraction of the solvent
The mole fraction of the solvent can be expressed as:
Xsolvent = `P_(solution)/P_(pure solvent)`
Substitute the values:
Xsolvent = `600/640` = 0.9375
Now, the mole fraction of the solute (Xsolute) is given by:
Xsolute = 1 − Xsolvent
Substitute the value of Xsolvent:
Xsolute = 1 − 0.9375
= 0.0625
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