Question

2.56g of sulphur (colloidal sol) in 100 ml solution shows Osmotic pressure of 2.463 atm at ${27}^{0}C$. How many sulphur atoms are associated in colloidal sol ? [Solution constant = 0.0821 atm.${mol}^{-1}{k}^{-1}$]

• A. 2
• B. 4
• C. 5
• D. 8

Answer 1

The correct option is D 8

Osmotic pressure $\left(\pi \right)=\frac{WRT}{MV}$

where,

$W=$ weight of sulphur (given)

$R=0.0821$ atm.mol ${}^{-1}{K}^{-1}$

$T={27}^{\circ }C=300k$

$V=$ volume of solution $=100ml=0.1L$

$\therefore M=\frac{WRI}{\pi v}$

$M=\frac{2.56\times 0.0821\times 300}{2.463\times 0.1}=256{gmol}^{-1}$

Associated number of atoms $=\frac{M}{\text{molar mass}\left(S\right)}$

$=\frac{256}{32}=8$