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 $1m{m}^3$. What is the average number of stearate ions (in multiples of ${10}^6$) in one colloidal particle (micelle)?

• A. 30
• B. 40
• C. 50
• D. 60

Answer 1

The correct option is A 30

Concentration $=1.2\times {10}^{3}M$
1 $m{m}^3$ will contain $\frac{1.2\times {10}^{3}mol/d{m}^3}{{10}^{6}m{m}^3/d{m}^3}=1.2\times {10}^{-3}$ moles of soap.
1 mole of soap $=6.023\times {10}^{23}$ molecules
$1.2\times {10}^{-3}$ moles of soap $=1.2\times {10}^{-3}\times 6.023\times {10}^{23}=7.227\times {10}^{20}$ stearate ions.
The average number of stearate ions in one colloidal particle (micelle) $=\frac{7.227\times {10}^{20}}{2.4\times {10}^{13}}=3\times {10}^7$