Question

The solubility of substance $X$ in pure ethanol is $0.1g/L$ and in water is $0.01g/L$. To dissolve $11g$ of dry $X$ we are adding $20ml$ of fresh $50\%(V/V)$ ethanol solution in each time on $X$. How many times we are to add this ethanol solution to dissolve $X$?

• A. $100$
• B. $10^6$
• C. $10^3$
• D. $10^4$

Answer 1

Answer: (D)

Each time we are adding $20ml$ ethanol solution. In $20ml$ ethanol solution vol. $C_2{H}_{5}OH=10ml$ and vol. of water $=10ml$

In $10ml$ ethanol mass of " $X$'' dissolved $=\frac{0.1}{1000}\times 10g$

In $10ml$ water mass of ''$X$'' dissolved $=\frac{0.01}{1000}\times 10g$

In each time, total mass of " $X$ ''dissolved $=\frac{1.1}{1000}g$

$\therefore$ No. of times of addition of ethanol solution

$=\frac{11}{1.1}\times 1000=10^4$