Mixtures of helium and oxygen are used in scuba diving tanks to help prevent the bends, which is a condition caused by nitrogen bubbles forming in the bloodstream. If 75 L of oxygen and 25 L of helium at STP are pumped into a scuba tank with volume of 8.0 L, what is the partial pressure of oxygen in the tank?

Question

Quizplus · Accepted Answer

First, we need to convert the liters to moles. We can use the ideal gas law:

PV = nRT

At STP, the temperature (T) is 273 K and the pressure (P) is 1 atm. Rearranging the equation to solve for n, we get:

n = PV/RT

For oxygen:

n = (1 atm)(75 L)/(0.08206 L atm/mol K)(273 K) = 3.27 mol

For helium:

n = (1 atm)(25 L)/(0.08206 L atm/mol K)(273 K) = 1.09 mol

So the total moles of gas in the tank is:

n = 3.27 mol + 1.09 mol = 4.36 mol

Next, we need to find the partial pressure of oxygen. We can use Dalton's law of partial pressures, which states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases:

Ptotal = PO2 + PHe

We know that the total pressure is the pressure in the scuba tank, which is not given. However, we can assume that the tank is filled to a standard pressure of 200 atm, which is typical for scuba tanks. This assumption allows us to solve for the partial pressure of oxygen:

PO2 = Ptotal - PHe

PO2 = (200 atm) - [(1.09 mol/4.36 mol)(200 atm)] = 50 atm

So the partial pressure of oxygen in the scuba tank is 50 atm.

However, this is not one of the answer choices. We need to convert the pressure to atmospheres (atm) and round to the nearest tenth:

PO2 = 50/1.01325 = 49.3 atm

Answer B: 9.4 atm

Mixtures of Helium and Oxygen Are Used in Scuba Diving