We have a methanol solution that is 6.0 m methanol, CH 3OH in water. Vapor pressure pure water at 30. degrees C is 31.82 mmHg. Vapor pressure methanol at 30. degrees C is 170.0 mm Hg. What is the total pressure above the solution at 30. degrees C

The total pressure above the solution at 30°C is 45.29 mmHg

Explanation:

We are given:

Molality of methanol = 6.0 m

This means that 6.0 moles of methanol present in 1 kg or 1000 g of pure water

To calculate the number of moles, we use the equation:

Given mass of water = 1000 g

Molar mass of water = 18 g/mol

Putting values in above equation, we get:

Mole fraction of a substance is given by:

To calculate the total pressure, we use the equation given by Dalton and Raoults, which is:

where,

= total vapor pressure  = ?

We are given:

Mole fraction of methanol = 0.0975

Mole fraction of water = 0.9025

Vapor pressure of methanol = 170.0 mmHg

Vapor pressure of water = 31.82 mmHg

Putting values in above equation, we get:

Hence, the total pressure above the solution at 30°C is 45.29 mmHg

the answer is option a.