# How do you calculate the vapor pressure of water above a solution prepared by adding 22.5 g of lactose [#C_12H_22O_11# ]tp 200 grams of water at 338 K?

##### 1 Answer

We need (i) the mole fractions of water in the solution; and (ii) the vapour pressure of pure water at

#### Explanation:

And (ii) we need the vapour pressure of pure water at this temperature. This site quotes the vapour pressure of PURE water at

Now the vapour pressure of the solution will be proportional to the mole fraction of each component.......

And as is required for a binary solution, the sum of the mole fractions is equal to unity.......

But

And thus at