Calculate the freezing point depression (T f ) of an aqueous 0.25 m K 2 SO 4 sol

Question

Calculate the freezing point depression (Tf) of an aqueous 0.25 m K2SO4 solution.

[HINT: Example 14.11 on p. 540 of your textbook gives an example of how to solve this type of problem. Use the information in Table 14.7 on p. 539 for van’t Hoff Factors.]

0.8 °C

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You dissolve 2.50 g of Na2SO4 in 500.0 mL of water. What is the vapor pressure of this solution at 30 °C? The vapor pressure of water at 30 °C is 31.8 torr and the density is 0.9957 g/mL.

[HINT: Example 14.12 on p. 541 of your textbook gives an example of how to do this type of problem.]

Explanation / Answer

Ans 1. b) 1.2 oC

Delta Tf = i.Kf .m

Where Kf is the cryoscopic constant of water = 1.86 0C kg/mol

and i is the vant hoff factor which is little less than 3 for K2SO4

So putting the terms in the formula

Delta Tf = 3x 1.86 x 0.25

Delta Tf = 1.395

So the freezing point depression will be little less than i.e. 1.20C

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