density and ideal gas law?

Question

What is the density of nitrogen gas (molecular mass = 28 u) at a pressure of 2.3 atmospheres and a temperature of 282 K?

Ok so first I converted the molecular mass to moles, which would be 2, and then I used the equation pv=nrt to get the volume, and then divided the volume by the mass, and got an answer of 1.4 but that is wrong. Any idea of what I'm doing wrong?

I'd appreciate any help.

Thanks.

Answer 1

> Ok so first I converted the molecular mass to moles, which would be 2,...

Not sure how you came up with that. 2 moles is a particular number of nitrogen molecules. (12×10^23, to be exact). But since the problem gives you no clue about how much nitrogen you're dealing with (it could be a tiny nitrogen bubble in a test tube, or a building full of nitrogen), there is no way you can calculate how many moles there are. That should be your first clue that you're going about it wrong.

Here's how I would do it:

n = number of moles = (mass in kg) / (molecular weight)

So:

n / v = mass / (molecular weight) / v
= (mass/v) / (molecular weight)
= density / (molecular weight)

So:

density = (molecular weight) (n / v)

From the ideal gas law:

n / v = P / (RT)

So:

density = (molecular weight) (P / (RT))

Answer 2

Density And Ideal Gas Law

Answer 3

Ideal Gas Law With Density

Answer 4

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RE:
density and ideal gas law?
What is the density of nitrogen gas (molecular mass = 28 u) at a pressure of 2.3 atmospheres and a temperature of 282 K?

Ok so first I converted the molecular mass to moles, which would be 2, and then I used the equation pv=nrt to get the volume, and then divided the volume by the mass, and got...

Answer 5

The reason why Nitrogen is not 2 moles is because Nitrogen gas exists as a diatomic molecule. There are 7 elements that exist in nature as diatomic--> I, Br, Cl, F, O, N, and H. So 1 mole of nitrogen gas weighs 28 grams because nitrogen gas is N2. However, 1 mole of Nitrogen atoms weighs 14g which is the value on the periodic table. Don't worry about it too much because this isn't gen chem, but just know that those 7 elements are diatomic.