Question

If a is the degree of dissociation of $Na_2SO_4$, the van’t Hoff factor (i) used for calculating the molecular mass is :

• A. $1-2\alpha$
• B. $1+2\alpha$
• C. $1-\alpha$
• D. $1+\alpha$

Answer 1

Answer: (B)

$Na_{2}SO_{4}\,{\rightleftharpoons}\,2Na^{+} + SO^{2-}_{4}$
van’t Hoff factor $i = \left[1 + \left(y - 1\right)\alpha\right]$
where $y$ is the number of ions from one mole solute, (in this case $= 3$), $\alpha$ the degree of dissociation.$\quad\quad i = \left(1 + 2\alpha\right)$