Chemistry Class 12 NCERT Solutions: Chapter 2 Solutions Part 13

Q: 30. Calculate the amount of benzoic acid Equation required for preparing Equation of Equation solution in methanol.

Answer:

Equation solution of benzoic acid in methanol means,

Equation of solution contains Equation mol of benzoic acid

Therefore, Equation mL of solution contains Equation of benzoic acid

Equation of benzoic acid

Molar mass of benzoic acid Equation Equation

Equation

Hence, required benzoic acid Equation

Equation

Q: 31. The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.

Among H, Equation , and F, H is least electronegative while F is most electronegative. Then, F can withdraw electrons towards itself more than Equation and H. Thus, trifluoroacetic acid can easily lose Equation ions i.e., trifluoroacetic acid ionizes to the largest extent. Now, the more ions produced, the greater is the depression of the freezing point. Hence, the depression in the freezing point increases in the order:

Acetic acid < trichloroacetic < trifluoroacetic acid

Q: 32. Calculate the depression in the freezing point of water when 10 g of Equation is added to Equation of water. Equation , Equation Equation .

Answer:

Molar mass of Equation

Equation

∴ No. of moles present in 10 g of Equation

Equation

It is given that 10 g of Equation is added to Equation of water.

∴ Molality of the solution, Equation

Equation

Let α be the degree of dissociation of Equation

Equation undergoes dissociation according to the following equation:

Equation

Equation

Equation

Since αis very small with respect to Equation

Now, Equation

Equation

Equation

Equation Equation

Equation

Again,

Equation

Total moles of equilibrium Equation

Equation

Equation

Equation

Equation

Equation

Hence, the depression in the freezing point of water is given as:

Equation

Equation

Equation

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