November 18th, 2009
How to calculate the partial pressure of each gas and the tpta; pressure in a tank?
Mixtures of helium and oxygen are used in scuba diving tanks to help prevent "the bends." For a particular dive, 46L He at 25 C and 1.0 atm and 12 L of O_2 at 25 C and 1.0 atm were pumped into a tank with a volume of 5.0 L. So…. calculate the partial pressure of each gas and the tpta; pressure in a tank at 25 C.
Helium is an inert gas, but will it react with oxygen in a high-pressure atmosphere? (I’ll assume not.) If not, then I’m going to use Dalton’s Law of Partial Pressures to say that the total pressure of the mixture = the sum of the partial pressures of each gas, and that the partial pressures inside the tank will be a ratio of what they were outside.
Now, from your question, we have that 46L of He is being pumped into a tank with 12L of O2, or a total of 58L of gas is being squeezed into a 5L tank. As the 58L of gas is at 1 atm, I’d have to guess the total pressure of the gas can be found by examining the proportions:
P1 = 1 atm
V1 = 58L
P2 = ?
V2 = 5L
P1*V1 = P2*V2
(1 atm)(58L) = P2*(5L)
11.6 atm = P2 (total pressure in the tank)
Again, I’m guessing that the partial pressures inside the tank are a ratio of what they were outside, meaning:
He:
V(He)/V(total) = P(He)/P(total)
46L/58L = P(He)/11.6
11.6*(46/58) = P(He)
9.2 atm = P(He)
P(O2) = 11.6 = 9.2 = 2.4 atm
It’s been a long time since I’ve had a chemistry course, but I have a few old textbooks here that are (somewhat) refreshing my memory.
November 18th, 2009
wheezer_april_4th_1966 Says :
Helium is an inert gas, but will it react with oxygen in a high-pressure atmosphere? (I’ll assume not.) If not, then I’m going to use Dalton’s Law of Partial Pressures to say that the total pressure of the mixture = the sum of the partial pressures of each gas, and that the partial pressures inside the tank will be a ratio of what they were outside.
Now, from your question, we have that 46L of He is being pumped into a tank with 12L of O2, or a total of 58L of gas is being squeezed into a 5L tank. As the 58L of gas is at 1 atm, I’d have to guess the total pressure of the gas can be found by examining the proportions:
P1 = 1 atm
V1 = 58L
P2 = ?
V2 = 5L
P1*V1 = P2*V2
(1 atm)(58L) = P2*(5L)
11.6 atm = P2 (total pressure in the tank)
Again, I’m guessing that the partial pressures inside the tank are a ratio of what they were outside, meaning:
He:
V(He)/V(total) = P(He)/P(total)
46L/58L = P(He)/11.6
11.6*(46/58) = P(He)
9.2 atm = P(He)
P(O2) = 11.6 = 9.2 = 2.4 atm
It’s been a long time since I’ve had a chemistry course, but I have a few old textbooks here that are (somewhat) refreshing my memory.
References :
November 18th, 2009
solario19 Says :
use the ideal gas law and the values for helium and for oxygen, solve for pressure for each. that will be the partial pressure for the two gases separately.
to find the total pressure simply add up the two partial pressures.
References :