As a research chemist, you are interested in studying the extent and types of in

Question

As a research chemist, you are interested in studying the extent and types of interactions in aqueous salt solutions. As part of this study, you weigh three samples of NaCl and dissolve each in 1.000 kg H_2 O. You then measure the freezing temperature of each solution and compare these temperatures to the freezing point of water. The data you collect are tabulated below. Explain the observed results. Predict and briefly explain the result you would expect for a solution made up of 29.22 g NaCl dissolved in 1.000 kg H_2 O.

Explanation / Answer

The depression in freezing point is given as

Delta Tf = i. Kf. m

where i is vant hoff's factor , kf is the cryoscopic constant of water = 1.86oC Kg/mol and m is the molality.

So lets determine vant ho0ff factor for NaCl using the observed results

m = [5.845 / 58.45] / 1 = 0.1

0.348 = i . 0.1 x 1.86

i = 1.9

Now 29.22 = 29.22 / 58.45 = 0.5 moles ,

m = 0.5 / 1 = 0.5

Delta Tf = 1.9 x 1.86 x 0.5

Delta Tf = 1.767oC

So the depression in freezing point in the solution will be observed as 1.767oC.

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