Question

The partial pressure of $O_2$ in air is $0.21atm$ at sea level. If aquatic life requires a concentration of $O_2$ at least $4.16mg/litre$, will the aquatic life sustain in sea level lake. $K_H$ for $O_2$ is $1.3\times {10}^{-3}mol/litre-atm$.

• A. $0.82mg/litre$
• B. $0.87mg/litre$
• C. $0.95mg/litre$
• D. $0.9mg/litre$

Answer 1

Answer: (B)

$0.87mg/litre$

Total pressure is 1 atm. The mole fraction of oxygen is 0.21.
Hence, the partial pressure of oxygen is $0.21\times 1=0.21atm$
According to Henry's law, $S=KP$
S is the solubility in moles per litre
K is the henry's law constant
P is the pressure in atm.
Substitute values in the above expression.
$S=1.3\times {10}^{-4}Mat{m}^{-1}\times 0.21atm=2.73\times {10}^{-5}M$
Thus $2.73\times {10}^{-5}$ moles of oxygen are dissolved in 1 L of water.
This corresponds to $2.73\times {10}^{-5}\times 32=8.736\times {10}^{-4}\text{g}or0.8736mg$ of oxygen in 1 liter of solution.