Question

Explain why equimolar aqueous solutions of nacl and na2so4 are not isotonic?

Answer 1

nacl gives two ions and na2so4 gives 3 ions so concentration of ions become different due to which the osmotic pressure become different so they are not isotonic

Answer 2

Answer: Because they have different vant hoff factor.

Explanation: Isotonic solutions are those solutions which have the same osmotic pressure.  If osmotic pressures are equal at the same temperature, concentrations must also be equal.  

$\pi =iCRT$ for electrolytes

$\pi$ = osmotic pressure

C= concentration

R= solution constant

T= temperature

i= vant hoff factor

1) For $NaCl$ , when it undergoes complete dissociation, i= 2

$NaCl\rightarrow Na^++Cl^-$

2)  For $Na_2SO_4$ , when it undergoes complete dissociation, i= 3

$Na_2SO_4\rightarrow 2Na^++SO_4^{2-}$

Thus even if the molarity and temperature is same, osmotic pressures will be different.