Problem: A solution contains 0.111 mol H2O and an unknown number of moles of sodium chloride. The vapor pressure of the solution at 30 oC is 25.7 torr. The vapor pressure of pure water at this temperature is 31.8 torr.Calculate the number of grams of sodium chloride in the solution. (Hint: Remember that sodium chloride is a strong electrolyte.)

FREE Expert Solution

We’re being asked to determine the grams of sodium chloride in the solution.


The vapor pressure of a solution can be given by Raoult’s Law:

Psolution = P°solventχsolvent


where P˚ = vapor pressure of solvent and χ = mole fraction of solvent.


The mole fraction of a solvent is given by:

χsolvent = moles solventi(moles solute) + moles solvent

where i = van’t Hoff factor.


We will do the following steps to solve the problem:

Step 1: Calculate the mole fraction of the solvent

Step 2: Calculate the moles of NaCl

Step 3: Calculate the grams of NaCl

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Problem Details

A solution contains 0.111 mol H2O and an unknown number of moles of sodium chloride. The vapor pressure of the solution at 30 oC is 25.7 torr. The vapor pressure of pure water at this temperature is 31.8 torr.

Calculate the number of grams of sodium chloride in the solution. (Hint: Remember that sodium chloride is a strong electrolyte.)

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the The Colligative Properties concept. You can view video lessons to learn The Colligative Properties. Or if you need more The Colligative Properties practice, you can also practice The Colligative Properties practice problems.

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Based on our data, we think this problem is relevant for Professor Bailey's class at Oklahoma City Community College.