Calculate the vapor pressure at 25 °C of an aqueous solution
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Question

Calculate the vapor pressure at 25 °C of an aqueous solution 
that is 5.50% NaCl by mass. (Assume complete dissociation of 
the solute.)

Accepted Answer

Hi everyone here we have a question telling us that an agreed solution is 3.25% potassium chloride by mass. What is its vapor pressure at 40°C assume that potassium chloride is completely dissociated in the solution. The vapor pressure of water at 40.0 degrees Celsius is 55. millimeters of mercury. So 3.25% potassium chloride means there are 3.25 g. A potassium chloride In 100 g of solution. So the mass of water Is going to equal 100 0.0 g -3.25g, Which is going to equal 96 .75g. Now we're going to calculate our mole fraction of water. So our moles of potassium chloride Equals 3.25 g times one mole. A potassium chloride over our molar mass, which is 74. g. So our g are going to cancel out here, leaving us with moles and that gives us 0. 36 moles of potassium chloride. Since potassium chlorate is fully dissociated, our potassium cool ride acquis is going to form potassium Aquarius plus chloride Aquarius. There are twice the solid particles in the salute than the moles of potassium chloride. So are solid particles Equals two times 0.0436 moles, Which equals 0.087. two moles. Our moles of water equals .75g of water times one mole Divided by our Molar Mass, which is 18.02g, Which equals 5. moles of water. So our mole fraction of water Equals 5.369 moles, Divided by 5.369 moles plus 0. moles, Which equals 0.9840. Now, to calculate the vapor pressure of our solution, the pressure of our solution equals our mole fraction of our solvent times the vapor pressure of our solvent, so our pressure of our solution Equals 0. times 55. millimeters of mercury. So the pressure of our solution equals 54 .4 mm of Mercury. And that is our final answer. Thank you for watching. Bye.

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