Question

Suppose you want to climb a mountain that is 19,000 feet tall. The air at that altitude has a total pressure of about half an atmosphere. The chemical composition of the air is the same as at sea level. Suppose you want to breathe the same partial pressure of oxygen that you normally would breathe at sea level – no more and no less. You decide to breathe bottled air from a tank, and adjust the composition of the air in the tank so you get the same PO2 that you’d normally get at sea level. 2. What should the composition of the air in your tank be? A. 21% 02 , the same as at sea level. B. 10.5% 02 . C. 42% 02 . D. It depends on the pressure in the tank. The higher the pressure, the lower the 02 concentration should be.

Answer 1

partial pressure of oxygen at sea level is = pressure at sea level X percentage availability

= 1 atm X 20.9%

if the same partial pressure has to be maintained at 19000 feet where pressure is decreased to 0.5 atm the oxygen concentration has to be increased

= 1 atm X 21%= 0.5 atm X (conc. of oxygen needed)

therefore, conc. of oxygen needed= 1 X 21/0.5

= 42%