Question

Which is the correct expression of van't Hoff factor for dissociation of electrolyte?
Here,
n is the number of ions formed from one formula unit of the substance

• A. $i=1+(n-2)\alpha$
• B. $i=1+(n-1)\alpha$
• C. $i=1+(n+1)\alpha$
• D. $i=1-(n+1)\alpha$

Answer 1

The correct option is B $i=1+(n-1)\alpha$

Dissociation of electrolyte:
$A_x{B}_y\left(aq\right)\rightleftharpoons x{A}^{y^{+}}+y{B}^{x^{-}}$
$t=0:C00$
$t=t_{eq}:C(1-\alpha )xC\alpha yC\alpha$

At equilibrium,
$\text{Net concentration}=C-C\alpha +xC\alpha +yC\alpha$
$=C[1+(x+y-1\left)\alpha \right]$
$=C[1+(n-1\left)\alpha \right]$
n is the number of particles in which 1 molecule of electolyte dissociates.
$i=\frac{C[1+(n-1\left)\alpha \right]}{C}$
$i=1+(n-1)\alpha$