Question

An aquatic species need at least 4mg/L of $O_2$ for their survival. $O_2$ in water at 273K and 1 atm pressure is $2.21\times {10}^{-3}$ mol/L. The partial pressure of $O_2$ above water(in an atmosphere at 273K) needed for the survival of species is:

• A. 0.56 atm
• B. 0.056 atm
• C. 5.525 atm
• D. 5.525 $\times$10${}^{-3}$ atm

Answer 1

The correct option is A 0.56 atm

Given, required solubility of oxygen gas for the survival of marine species=4mg/L

We know 1 mole of oxygen $=32g$ of oxygen

0.004g of $O_2=125\times {10}^{-6}mol/L$

Now we know initial pressure above water = 1 atm

Also given,

Initially solubility of $O_2$ gas in water at 1 atm $=2.21\times {10}^{-3}mol/L$

Now,we know according to Henry's law of partial pressure.

Solubility of gas is directly proportional to partial pressure of that gas over liquid.

$S\propto P$

$\frac{S_1}{S_2}=\frac{P_1}{P_2}$

$\frac{2.21\times {10}^{-3}}{125\times {10}^{-6}}=\frac{1}{P_2}$

$P_2=0.056atm$