Question
How much oxygen is dissolved in $$100\,mL$$ water at $$298\,K$$ if partial pressure of oxygen is $$0.5\,atm$$ and $${K_H} = 1.4 \times {10^{ - 3}}\,mol/L/atm?$$
A.
22.4$$\,mg$$
B.
22.4$$\,g$$
C.
2.24$$\,g$$
D.
2.24$$\,mg$$
Answer :
2.24$$\,mg$$
Solution :
According to Henry's law, $$s = {K_H} \times p,$$ where $$s$$ is concentration of $${O_2}$$ dissolved.
$$\eqalign{
& s = 1.4 \times {10^{ - 3}} \times 0.5 = 0.7 \times {10^{ - 3}}\,mol/L \cr
& s = \frac{n}{V}\,\,\,{\text{or}}\,\,\,n = 0.7 \times {10^{ - 3}} \times 0.1 = 0.7 \times {10^{ - 4}}\,mol \cr
& n = \frac{w}{M}\,\,\,{\text{or}}\,\,\,w = n \times M \cr
& \,\,\,\,\,\, = 0.7 \times {10^{ - 4}} \times 32 \cr
& \,\,\,\,\,\, = 22.4 \times {10^{ - 4}}\,g\,\,\,{\text{or}}\,\,\,2.24\,mg \cr} $$