Solutions Question 346
Question: A molecule M associates in a given solvent according to the equation $ M\rightarrow {{(M)}_{n}} $ . For a certain concentration of M, the van’t Hoff factor was found to be 0.9 and the fraction of associated molecules was 0.2. The value of n is:
Options:
A) 3
B) 5
C) 2
D) 4
Show Answer
Answer:
Correct Answer: C
Solution:
van ’t Hoff factor (i) and the degree of association are related as below: $ i=1-\alpha ( 1-\frac{1}{n} ) $
$ 0.9=1-0.2( 1-\frac{1}{n} ) $ On solving, $ ( 1-\frac{1}{n} )=\frac{1}{2} $
$ \frac{1}{n}=1-\frac{1}{2}=\frac{1}{2} $
$ \therefore n=2 $
