Question

2 gm/l of sol of nacl is isotonic with 7.2 gm/l of solu of glucose calculate the vant hoff factor of nacl solution

Answer 1

NaCl is ionic compound so, osmotic pressure of NaCl is given by, $\pi_{NaCl}=\iota CRT$

where, C is concentration of NaCl. but density, d of solution is given then, osmotic pressure is $\pi_{NaCl}=\iota\frac{dRT}{M}$

so, osmotic pressure of NaCl, $\pi_{NaCl}=\iota\frac{2RT}{58.5}$

now in case of glucose, it is covalent compound. it can't be dissociated into ions. so, osmotic pressure is, $\pi_{glucose}=\frac{dRT}{M}$

= 7.2RT/60

NaCl solution is isotonic with glucose.

so, $\pi_{NaCl}=\pi_{glucose}$

or, i 2RT/58.5 = 7.2RT/60

0r, 2i/58.5 = 0.12

or, i/58.5 = 0.06

or, i = 58.5 × 0.06 = 3.51

hence, Van't Hoff's factor is 3.51