Question

Question 15. a) What pressure in atm of gas from a scuba regulator would equal the air plus water pressure at a depth of 100 m (328 feet)? Show work

b) What percent of a He/O2 mix would have to be O2 to make the partial pressure of O2 0.21 atm when the pressure of the mix is the value in 15.a. Show work

Answer 1

Question 15a)

Density of water, d = 1000 kg/m³

Depth, h = 100 m

Gravity, g = 9.81 m/s²

Atmospheric Pressure, P_o = 1 atm

Water Pressure, P_w =d * g * h = (1000 kg/m³)* (9.81 m/s²) * (100 m ) = 98100 Pa

We need it in atm,

P_w = 981000 Pa = 981000 Pa * (1 atm /101325 Pa) = 9.68 atm

Total Pressure= P_o + P_w = 1 atm + 9.68 atm = 10.68 atm

Question 15b)

Total pressure = 10.68 atm

Partial pressure of oxygen, p_o2 = 0.21 atm

mole fraction of Oxygen = p_O2/P = 0.21 atm / 10.68 atm = 0.0197 = 0.020 (2 sig fig)

% of Oxygen = 0.020* 100 % = 2.0%

Mole fraction and volume fractions are same.

Thus, Oxygen will have to 2.0 % v/v