Question

Which one of the following electrolytes has the same value of van't Hoff factor $\left(i\right)$ as that of $K_{4}Fe(CN{)}_6$ (if all are 100% ionised)?

• A. $N{a}_{2}S{O}_4$
• B. $Al(N{O}_3{)}_3$
• C. $NaCl$
• D. $A{l}_2(S{O}_4{)}_3$

Answer 1

The correct option is D $A{l}_2(S{O}_4{)}_3$

$K_4\left[Fe\right(CN{)}_6]$ dissociates as:
$K_4\left[Fe\right(CN{)}_6]\stackrel{So{l}^n}{⟶}4K^{+}+1[Fe(CN{)}_6{]}^{-4}$
Van't Hoff factor:
$i=5$
Option (a):
$A{l}_2(S{O}_4{)}_3\stackrel{So{l}^n}{⟶}2A{l}^{+3}+3S{O}_4^{-2}$
Van't Hoff factor :
$i=5$

Option (b) :
$NaCl\stackrel{So{l}^n}{⟶}N{a}^{+}+C{l}^{-}$
Van't Hoff factor :
$i=2$
Option (c) :
$Al(N{O}_3{)}_3\stackrel{So{l}^n}{⟶}1A{l}^{+3}+3N{O}_3^{-}$
Van't Hoff factor :
$i=4$
Option (d) :
$N{a}_{2}S{O}_4\stackrel{So{l}^n}{⟶}2N{a}^{+}+1S{O}_4^{2-}$
Van't Hoff factor :
$i=3$
Only option (a) i.e. $A{l}_2(S{O}_4{)}_3$ has the same value of Van't Hoff factor as that of $K_{4}Fe(CN{)}_6$
Option (a) is correct.