How does vapor pressure lowering lead to freezing point depression and boiling p

Question

How does vapor pressure lowering lead to freezing point depression and boiling point elevation?

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You add 1.00 kg of the antifreeze ethylene glycol (C2H6O2) to your car radiator, which contains 4450 g of water. What is the freezing point of the solution?

[HINT: Example 14.9 on p. 536 of your textbook gives an example of how to solve this type of question. The constants, freezing points, and boiling points that you will need for this problem are found in Table 14.6 on p. 535 of your textbook.]

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Find the boiling point of the solution described in the previous question.

[HINT: Example 14.9 on p. 536 of your textbook gives an example of how to solve this type of question. The constants, freezing points, and boiling points that you will need for this problem are found in Table 14.6 on p. 535 of your textbook.]

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Biochemists have discovered more than 400 mutant varieties of hemoglobin, the blood protein that carries oxygen throughout the body. A physican studying a variety associated with a fatal disease finds its molar mass. She dissolves 21.5 mg of protein in water at 5.0 °C to make 1.50 mL of solution and measures an osmotic pressure of 3.61 torr. What is the molar mass of this hemoglobin variety?

[HINT: Example 14.10 on p. 538 of your textbook gives an example of how to solve this type of problem.]

9.98 x 102 g/mol

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Explanation / Answer

How does vapor pressure lowering lead to freezing point depression and boiling point elevation?

Best answer is:

It shifts the vaporization curve in a phase diagram downward and the fusion curve to the left.

Since --> Vapor pressure decreases as we add solute, that implies a decrease in P°, i.e. downward

For the fusion --> recall that the solid/liquid line is left/right, so the liquid will increase itstemperature range, meaning that T must go to the left

You add 1.00 kg of the antifreeze ethylene glycol (C2H6O2) to your car radiator, which contains 4450 g of water. What is the freezing point of the solution?

Apply

dTf = -Kf*m

m = mol of S / kg solvent = mass / MW /(Kg) = 1000/ 62.07 / 4.45 = 3.62 molal

Kf = 1.86 for water

dTf = 1.86*3.62 = 6.73 °C

Tf = T0 - dTf = 0 - 6.73 = -6.73 °C

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