Question

A soap $\left(C_{17}{H}_{35}COONa\right)$ solution becomes a colloidal sol at a concentration of $1.2\times {10}^{-3}M$. On the average, $2.4\times {10}^{13}$ colloidal particles are present in $1{mm}^3$. What is the average number of stearate ions in one colloidal particle (micelle)?

• A. $30$
• B. $40$
• C. $50$
• D. $60$

Answer 1

The correct option is A $30$

The concentration of soap solution is $1.2\times {10}^{-3}moles/d{m}^3=1.2\times {10}^{-9}mole/m{m}^3$

This corresponds to $6.02\times {10}^{23}\times 1.2\times {10}^{-9}=7.2\times {10}^{14}molecules/m{m}^3$

Total number of colloidal particles in $1m{m}^3$ are $2.4\times {10}^{13}$.

Hence, the number of sterate ions in one particle are $\frac{7.2\times {10}^{14}}{2.4\times {10}^{13}}=30$

Hence, option $A$ is correct.