4. ATr Kfx concentration. What does ATr stand for ? What does Kr stand for ? Wha

Question

4. ATr Kfx concentration. What does ATr stand for ? What does Kr stand for ? What are the units of the concentration used in this type of calculation? 5. A solvent has a freezing point of 32.6°C and Krs 9.75%gmol. A solution is made using 29.183 g of this solvent and 0.427 g of an unknown material. The solution has a freezing point of 30.7°C. a Calculate , for the solution (1) b. Calculate the concentration of the solution (give units) (2) b. Since the amount of solvent was 29.183 grams, how many moles of the solute were dissolved ? (2) Hint: you need kg of solvent to solve this. c. Since the mass of the solute was 0.427 grams, what is its molar mass? (2)

Explanation / Answer

4.

a) When a non volatile solute is added to a pure solvent then the freezing point of the solution decrease that is the freezing point of solution is less than the freezing point of pure solvent.

This difference in the freezing point is Tf and is called depression in freezing point.

b) This depression in freezing point is equal to Kf × molality of solution .

Kf is called molal depression constant or cryoscopic constant.

Since concentration = molality(m)

= mol of solute / mass of solvent in kg

So it's units are mol/kg or m

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