Depression of Freezing Point

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Depression of Freezing Point: Overview

This topic covers concepts such as freezing point, depression in freezing point, anti-freezing agents and molal freezing point depression constant using molar heat of fusion.

Important Questions on Depression of Freezing Point

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Calculate the freezing point of a solution containing 18 g glucose, C6H12O6and68.4gsucrose,C12H22O11in200g of water. The freezing point of pure water is 273 K and Kf for water is 1.86 K kg mol1.

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The freezing point of a solution containing 0.2 g of acetic acid in 20.0 g of benzene is lowered by 0.45°C. The molar mass (g/mol) of acetic acid from this data and the value of van’t Hoff factor would be (for benzene, Kf=5.12 K kg mol-1)

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Choose the correct statement?

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De-icing is the process of removing snow, ice or frost from a surface. In extremely cold regions, car windows get covered by ice reducing the visibility. The image below shows the de-icing of the window of a car during extreme cold using a fluid.

Question Image

Which of the following compounds could be present in the de-icing fluid used above?

MEDIUM
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An aqueous solution containing 3g of a solute of molar mass 111.6 g mol-1 in a certain mass of water freezes at -0.125°C. The mass of water in grams present in solution is Kf=-1.86K kg mol-1

MEDIUM
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An aqueous solution of sodium chloride freezes below 273 K. Explain the lowering in freezing point of water with the help of a suitable diagram.

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At TKxg of a non-volatile solid (molar mass 78 g mol-1 ) when added to 0.5 kg water, lowered its freezing point by 1.0°C. What is x (in g) (Kf of water at T(K)=1.86 KKgmol-1)

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The freezing point depression constant Kf of benzene is 5.12Kkg mol-1. Assuming 100% dimerization of acetic acid in benzene, the freezing point depression of 0.2m solution of acetic acid is

MEDIUM
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1.02 g of urea when dissolved in 98.5 g of certain solvent decreases its freezing point by 0.211K. 1.609 g of an unknown compound when dissolved in 86 g of the same solvent depresses the freezing point by 0.34 K. Calculate the molar mass of the unknown compound.

(Molar mass of urea = 60 g mol-1 )

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What is a de-icing agent? How does it work?

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What freezes out first when a solution of common salt is cooled?

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Why is camphor preferred as a solvent in finding the molecular mass of naphthalene by Rast method?

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Which of the following solution will have the lowest freezing point and why ? (i) 0.1 M NaCl solution (ii) 0.1 M glucose solution (iii) 0.1 M BaCl2 solution 

 

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Which of the following solution will have the lowest freezing point and why? (i) 0.1 M NaCl solution (ii) 0.1 M glucose solution (iii) 0.1 M BaCl2 solution.

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What is an antifreeze?

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Between 2 M glucose solution and 1 M glucose solution, which one has a lower freezing point?

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Give one most important application of the phenomenon of depression in the freezing point in everyday life.

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Define molal depression constant/ cryoscopic constant.

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 A solution of glucose (Molar mass = 180 g mol-1) in water has a boiling point of 100.20°C. Calculate the freezing point of the same solution. Molal constants for water Kf and Kb are 1.86 K kg mol-1 and 0.512 K kg mol-1 respectively.

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 A 0.1539 molal aqueous solution of cane sugar (mol. mass = 342 g mol-1) has a freezing point of 271 K while the freezing point of pure water is 273.15 K. What will be the freezing point of an aqueous solution containing 5 g of glucose (mol. mass = 180 g mol-1) per 100 g of solution.