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JEE Main 202227 JuneMorning Shift
Exam
JEE Main
Year
2022
Date
27 June
Shift
Morning Shift
Subject
Chemistry
Chapter
Solutions

JEE Main 2022 · 27 June · Morning Shift · Chemistry · Solutions

Given below are two statements : one is labelled as Assertion and...

Given below are two statements : one is labelled as Assertion and the other is labelled as Reason.

Assertion: At 10°C10 ° C, the density of a 5M5M solution of KClKCl [atomic masses of K and ClK \text{ and } Cl are 39 and 35.5gmol−139 \text{ and } 35 . 5g{mol}^{- 1} respectively], is 'xx' gml−1{gml}^{- 1}. The solution is cooled to −21°C- 21 ° C. The molality of the solution will remain unchanged.

Reason: The molality of a solution does not change with temperature as mass remains unaffected with temperature.

In the light of the above statements, choose the correct answer from the options given below.

Options

  1. AAssertion is true but Reason is false.
  2. BAssertion is false but Reason is true.
  3. CBoth Assertion and Reason are true and Reason is the correct explanation of Assertion.
  4. DBoth Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Correct answer

C. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Step-by-step solution

The freezing point depression, ΔTf{\Delta T}_{f} is equal to the freezing point of the solvent minus the freezing point of the solution.

It is also proportional to the molal concentration of the solute.

ΔTf=Kfm\Delta{T}_{f} = {K}_{f}m

Where Kf{K}_{f}, the freezing point depression constant, depends only on the solvent. Molality is moles of solute per kg of solvent. So, the concentration of solvent is expressed in terms of mass, and the mass of a substance is not affected by the change in temperature. Hence, molality is independent of temperature.

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