Question

How much oxygen is dissolved in $100mL$ water at $298K$ if partial pressure of oxygen is $0.5atm$ and $K_H=1.4\times {10}^{-3}$ $mol/L/atm$?

• A. $22.4mg$
• B. $22.4g$
• C. $2.24g$
• D. $2.24mg$

Answer 1

Answer: (D)

$2.24mg$

According to Henry's law,

$S=K_H\times \text{Partial pressure of Oxygen}$

where S is a concentration of $O_2$ is dissolved, $K_H$ is Henry's constant and $X_P$ partial pressure of $O_2$.

Here, $K_H=1.4\times {10}^{-3}molperLperatm$ and $p_{O_2}=0.5atm$

So, $S=1.4\times {10}^{-3}\times 0.5=0.7\times {10}^{-3}M$

now, $molarity=\frac{numberofmoleofsolute}{volumeofsolution}$

or, $0.7\times {10}^{-3}=\frac{massof{O}_2}{molecularweightof{O}_2\times volumeofsolutioninL}$

or, $0.7\times {10}^{-3}=\frac{massof{O}_2}{32gpermole\times 0.1L}$

or $0.7\times {10}^{-3}\times 3.2=massof{O}_2$

or, $massof{O}_2=2.24\times {10}^{-3}g=2.24mg$

The correct option is D.