chemistry question I dont get

Question

Calculate the density of oxygen, O2, under each of the following conditions:

STP

1.00 bar and 35.0 ∘C

Express your answers numerically in g L−1. Enter the density at STP first and separate your answers by a comma.

please help I do not get this show all the work please I'm confuse

Answer 1

Hello, Kal,

Let's start with the density at STP (1 atm and 0 C) [the easiest to answer]. All gases at STP occupy 22.4 liters per mole of gas. Let's assume we have 1 liter of O₂ , for convenience. We can calculate the moles of O₂ present in that 1 liter by dividing by the useful 22.4 liters/mole conversion factor (at STP):

1 liter/(22.4 l/mole) = 0.04461 moles O₂

The molar mass of O₂ is 32 g/mole.

Therefore, we have (0.04461 moles O₂ )*(32 g/mole) = 1.428 grams O₂

Since we assumed 1 liter, we can now see that the density of O₂ is 1.428 g/liter.

For the question at 1 bar (atm) and 35 C, I use the ideal gas law. One can also use the combined gas law, but here is how the ideal gas law would work"

PV = nRT

We will again assume 1 liter, but since we are no longer at STP, we need to find the new number of moles:

n = PV/RT, where R is the gas constant and T is the temperature in Kelvin (add 273.15 to C).

n = (1atm)(1 L)/(0.08206 L*atm*K^-1mol^-1 )(308.15K)

n = 0.03955 moles O₂

This is a mass of (32 g/mole)*(0.03955 moles) = 1.266 grams O₂ .

Again, since we assumed 1 Liter, we can say the density of O₂ is 1.266 g/l at these conditions. The temperature was raised over the previous problem while the volume and pressure remained constant. It najkes sense that we'd wind up with fwerer moles of O₂. The it therefore makes sense that the sensity of O₂ is lower than before.

I hope this helps,

Bob