How Do You Calculate Vapor Pressure Of A Solution?
Chemistry students are often asked to estimate the vapor pressure of a solvent. The easiest way to calculate this value is to use a simple formula. You just have to plug some numbers in and calculate the pressure. Write the formula P = mole fraction of solvent X pressure of pure solution. Use a calculator to calculate the mole fraction of the solvent by dividing the number of moles of solvent by the total number of moles in the solution. For example, if you are studying a solution that has 20 moles of water and .5 moles of sugar, you would divide 20 moles by 20.5 moles, yielding a mole fraction of .98. Look up the vapor pressure of the pure solvent in a chemistry book or table. Rewrite the formula using the values you obtained. For example, using water at a temperature of 62 degrees and the mole fraction calculated in Step 2, you would rewrite the formula as P = .98 x 163.8 mmHg Perform the calculation to obtain an answer.
