A scuba tank contains heliox, a special breathing gas composed of 5.0% oxygen and the remainder helium, for use by divers that spend extended amounts of time at depth underwater. The volume of the tank is 20 L and the pressure within it is 1500 lb/in2. Calculate the mass in grams of each gas in the tank and their partial pressures at 20 degrees celsius.

(Well I have the molar mass of HeO2 at 35 g/mol but do I have to go through the process of turning grams to moles to moles to grams? And I am not entirely sure about the last part whether I am to find the partial pressure or the partial pressure is 20 degrees celsius. Am I overthinking this?)

Perhaps. Partial pressure is what you are to find and you should understand that partial pressure is NOT measured in degrees C but in atm or mm Hg or some other pressure unit. What you want to do is to convert 1500 lb/in^2 to atm Then use PV = nRT, substitute with the conditions listed and solve for n = number of mols (total) of the mixture. 5% times that will tell you how much He is there and the difference (or 95%) = mols O2. After you know mols you can go one of two ways.

1. Resubstitute individual mols and the other conditions into PV = nRT and solve for pHe and the same thing with mols O2 to find pO2.

2. OR you may convert mols He and mols O2 to mole fractions.
XO2 = mols O2/total mols.
XHe = mols He/total mols.
Then pO2 = XO2*Ptotal
and pHe = XHe*Ptotal

To calculate the mass of each gas in the scuba tank, you need to convert the given volume (20 L) and pressure (1500 lb/in2) into moles of gas. Since you already know the molar mass of Heliox (35 g/mol), you can directly calculate the mass in grams of each gas using the ideal gas law equation:

PV = nRT

Where:
P = pressure (in atm)
V = volume (in L)
n = number of moles
R = ideal gas constant (0.0821 L(atm)/(mol·K))
T = temperature (in Kelvin)

First, you need to convert the pressure from lb/in2 to atm. 1 lb/in2 is equal to 0.068046 atm. So, the pressure is 1500 x 0.068046 = 102.069 atm.

Now, you need to convert the volume from L to moles. To get the number of moles, divide the volume by the molar volume of an ideal gas at standard temperature and pressure (STP), which is 22.4 L/mol. So, 20 L is equal to 20/22.4 = 0.8929 mol.

Next, convert the temperature from Celsius to Kelvin. Add 273.15 to the Celsius temperature to get the Kelvin temperature. In this case, 20°C + 273.15 = 293.15 K.

Now, you can substitute the values into the ideal gas law equation to determine the number of moles (n) for each gas:

n = (PV) / (RT)

For Helium (He):
P(He) = 0.95 x 102.069 atm (since the oxygen makes up 5% of the mixture, helium constitutes the remaining 95%)
V = 0.8929 mol
R = 0.0821 L(atm)/(mol·K)
T = 293.15 K

n(He) = (0.95 x 102.069) x 0.8929 / (0.0821 x 293.15) = 3.232 mol

For Oxygen (O2):
P(O2) = 0.05 x 102.069 atm
V = 0.8929 mol
R = 0.0821 L(atm)/(mol·K)
T = 293.15 K

n(O2) = (0.05 x 102.069) x 0.8929 / (0.0821 x 293.15) = 0.135 mol

To convert the number of moles to grams, multiply the number of moles by the molar mass.

Mass(He) = 3.232 mol x 35 g/mol = 113.12 g
Mass(O2) = 0.135 mol x 32 g/mol = 4.32 g

So, the mass of helium in the tank is approximately 113.12 g, and the mass of oxygen is approximately 4.32 g.

Regarding the partial pressure, it is the pressure exerted by each component of a gas mixture as if it alone occupied the volume of the entire mixture at the same temperature. In this case, you are asked to calculate the partial pressures of each gas at 20 degrees Celsius.

The partial pressure of each gas can be calculated using Dalton's Law of partial pressures, which states that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of each gas. The partial pressure of each gas is given by the mole fraction of that gas multiplied by the total pressure.

Partial Pressure of Helium (P(He)) = (moles of helium / total moles) x total pressure

P(He) = (3.232 mol / (3.232 mol + 0.135 mol)) x 102.069 atm

Partial Pressure of Oxygen (P(O2)) = (moles of oxygen / total moles) x total pressure

P(O2) = (0.135 mol / (3.232 mol + 0.135 mol)) x 102.069 atm

By substituting the values, you can find the partial pressures of helium and oxygen in the tank.

I hope this helps clarify the process for calculating the mass and partial pressures of each gas in the scuba tank.