Question

A solution of sodium chloride in water has a vapor pressure of 19.6 torr at 25°C. What is the mole fraction of NaCl in this solution? The vapor pressure of pure water is 23.8 torr at 25°C.

Answer 1

Answer:

Mole fraction of Nacl is 0.173

Explanation:

we know that

$P_{sol}=\chi_{solvent}P^0_{solvent}$

where,

P sol  - the vapor pressure of the solution

χ  solvent - the mole fraction of the solvent

P ∘ solvent  - the vapor pressure of the pure solvent

This means that in order to be able to calculate the mole fraction of sodium chloride, you need to know what the vapor pressure of pure water is at  

25 ° C  You can use an online calculator to find that the vapor pressure of pure water at  25 C  is equal to about  23.8 torr .

$\chi_{water}= \frac{P{sol}}{P^0{water}}$

$\chi_{water}= \frac{19.6}{23.8}$

=0.827

Also we know that

$\chi_{water}+\chi_{Nacl}= 1$

This means that the mole fraction of sodium chloride is

χ_{Nacl}= 1-Χ_{water}

= 1-0.827 =0.173