Question

$12.2g$ benzoic acid $(M=122)$ in $100g{H}_{2}O$ has elevation of boiling point of ${0.27}^{\circ }C,k_b=0.54kkg/mole.$ If there is $100\%$ dimerization, the no. of molecules of benzoic acid in associated state is:

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

The correct option is B 2

As we know,
$\Delta T_b=i\times \frac{1000k_b{w}_2}{M_2{w}_1}$
$i=\frac{0.27\times 122\times 100}{1000\times 0.54\times 12.2}$
$i=0.5i=1-\alpha +\frac{\alpha }{n}$
$0.5=1-1+\frac{1}{n}n=2$