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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.

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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.

Sum
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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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