a. State Henry’s law and explain why are the tanks used by scuba divers filled with air diluted with helium

Question

Answer the following questions:

a. State Henry’s law and explain why are the tanks used by scuba divers filled with air diluted with helium (11.7% helium, 56.2% nitrogen and 32.1% oxygen)?

b. Assume that argon exerts a partial pressure of 6 bar. Calculate the solubility of argon gas in water. (Given Henry’s law constant for argon dissolved in water, K_H = 40kbar)

Answer 1

a. Henry’s law: the partial pressure of the gas in vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution.

The pressure underwater is high, so the solubility of gases in blood increases. When the diver comes to surface the pressure decreases so does the solubility causing bubbles of nitrogen in blood, to avoid this situation and maintain the same partial pressure of nitrogen underwater too, the dilution is done.

b. p = K_H x

mole fraction of argon in water x = p/k = 6/40 x 10³ = 1.5 x 10^-4