Problem: In ice-cream making, the ingredients are kept below 0.0°C in an ice-salt bath.(a) Assuming that NaCl dissolves completely and forms an ideal solution, what mass of it is needed to lower the melting point of 5.5 kg of ice to –5.0°C?(b) Given the same assumptions as in part (a), what mass of CaCl2 is needed?

FREE Expert Solution

Recall that the melting point is the same temperature as the freezing point.

The freezing point of a solution is lower than that of the pure solvent and the change in freezing point (ΔT­f) is given by:


ΔTf=Tf, pure solvent-Tf, solution


The change in freezing point is also related to the molality of the solution:


ΔTf=imKf


where: 

i = van’t Hoff factor

m = molality of the solution (in m or mol/kg)

Kf = freezing point depression constant (in ˚C/m)


Recall that the molality of a solution is given by:


molality=moles solutekg solvent


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Problem Details

In ice-cream making, the ingredients are kept below 0.0°C in an ice-salt bath.

(a) Assuming that NaCl dissolves completely and forms an ideal solution, what mass of it is needed to lower the melting point of 5.5 kg of ice to –5.0°C?
(b) Given the same assumptions as in part (a), what mass of CaCl2 is needed?

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Freezing Point Depression concept. If you need more Freezing Point Depression practice, you can also practice Freezing Point Depression practice problems.

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Based on our data, we think this problem is relevant for Professor Telesford's class at TTU.

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Our data indicates that this problem or a close variation was asked in Chemistry: The Molecular Nature of Matter and Change - Silberberg 8th Edition. You can also practice Chemistry: The Molecular Nature of Matter and Change - Silberberg 8th Edition practice problems.