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Van't Hoff Factor and Abnormal Molar Mass - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main

Quick Facts

  • van't Hoff factor(i) or Abnormal Colligative Property is considered one the most difficult concept.

  • Calculation of Extent of Dissociation in an Electrolytic Solution is considered one of the most asked concept.

  • 45 Questions around this concept.

Solve by difficulty

Which one of the following aqueous solutions will exhibit highest boiling point?

We have three aqueous solutions of NaCl labelled as 'A', 'B' and 'C' with concentration 0.1 M, 0.01 M and 0.001
M, respectively. The value of van 't Hoff factor(i) for these solutions will be in the order :

The values of Van't Hoff factors for KCl, NaCl, and K2SO4 are 

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The Van't Hoff factor for 0.1M Ba$\left(\mathrm{NO}_3\right)_2$ solution is 2.74. The degree of dissociation is

Which of the following statement(s) is/are correct regarding the colligative properties of a solution?

 

For electrolytes $A_2 B_3 \& A_3 B_2$ if degree of dissociation are $0.1 \& 0.2$ respectively then ratio of their van't Hoff factor is:

Colligative properties depend on ____________.

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If \alpha is the degree of dissociation of Na_{2}SO_{4} the Van't Hoff’s factor (i) used for calculating the molecular mass is

Concepts Covered - 3

van't Hoff factor(i) or Abnormal Colligative Property

If a solute gets associated or dissociated in a solution, the actual number of particles are different from expected or theoretical consideration.

We know, that:

\mathrm{Colligative\: property \propto number \: of \: particles}

Thus, we can say that:

\\\mathrm{i\: =\: \frac{Observed\: number\: of\: solute\: particles}{Number\: \: of\: particles\: initially\: taken}}\\\\\mathrm{i\: =\: \frac{Observed\: value\: of\: colligative\: property}{Theoretical\: value\: of\: colligative\: property}}\\

Again, we have:

\mathrm{Colligative\: property \propto\: \frac{1}{molecular\: mass\: of\: solute}}

Thus;

\mathrm{i\: =\: \frac{Theoretical\: molecular\: mass\: of \: solute}{Observed\: molecular\: mass\: of \: solute}}

 

Calculation of Extent of Dissociation in an Electrolytic Solution

van't Hoff Factor for dissociation of solute

Suppose we have the solute A which dissociates into n moles of A. Then the dissociation occurs as follows:

                         \mathrm{A_{n}\rightarrow nA}                    

At time t = 0         1          0

At time t = t       1 - \alpha      n\alpha

At time t = 0, initial number of solute particles = 1

And, at time t = t, observed number of solute particles = 1 - \alpha + n\alpha

                                                                                      = 1 + (n-1)\alpha

Thus, we know that:

\mathrm{i\: =\: \frac{observed\: number\: of\: solute\: particles}{initial\: number\: of\: solute\: particles}}

\mathrm{i\: =\: \frac{1+(n-1)\alpha }{1}}

where n = number of solute particles

         \alpha = Degree of dissociation

For strong electrolytes, the degree of dissociation is taken to be unity.

Using the above equation, the van’t Hoff factor and the degree of dissociation can be related which can be further related to the theoretical and observed colligative properties.

Calculation of Extent of Association in an Electrolytic Solution

Suppose we have a solute A and it associates into (A)nThen the association occurs as follows:

                        nA\rightarrow \left ( A \right )_{n}

At time t = 0        1            0

At time t = t       1 - \beta       \beta/n

Now, the initial number of solute particles = 1

And, the observed number of solute particles = 1-\beta+\frac{\beta }{n}

                                                            =1+\beta\left [ \frac{1}{n}-1 \right ]

Thus, van't Hoff factor is given as:

i=1+\beta\left [ \frac{1}{n}-1 \right ]

where, \beta is the degree of association

Using the above equation, the van’t Hoff factor and the degree of association can be related which can be further related to the theoretical and observed colligative properties.

Study it with Videos

van't Hoff factor(i) or Abnormal Colligative Property
Calculation of Extent of Dissociation in an Electrolytic Solution
Calculation of Extent of Association in an Electrolytic Solution

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