can someone help me with this environmentalchem problem?

Question

what is the concentration of neon in the atmosphere in molecules per L assuming an atmospheric pressure of 743 torr and a temperature of 295 Deg Celcius. the mole fraction of neon in dry air is 0.00001818moles.

is the formula PV= NRT used?

Answer 1

You have the mole fraction of Neon in air and you know that one mole contains 6.022 * 10^23 molecules (if you assume the gas behaves like an Ideal Gas).

First, the Temperature must be either incorrect or very hot. I will assume that you mean 295 °K (which is only 22 °C).

To find the number of moles of Air:
PV = nRT or n = PV/RT (using R = 62.3637 L-torr/°K-mole)

n = (743 torr*1.00 L)/(62.36 L-torr/°K-mole)(295 °K)
= 743 / 18396 = 0.0404 moles of Air

The moles of Neon = 0.0404 * 0.00001818 = 0.000000734 moles (this is 7.34*10^-7), so the number of molecules is:

6.022 * 10^23 molecules/mole * 7.34*10^-7 moles
= (6.022 * 7.34) * (10^23 * 10^-7)
= 44.20 * 10^16 = 4.420 * 10^17 molecules / L

Check my math, but this is how it should be done.

Answer 2

yes i think so...
N=PV/RT AND N = CV can be put together to get
CV=PV/RT
THE V'S CANCEL OUT WHICH LEAVES U WITH C= P/RT
PLUG IT IN, DONT FORGET TEMPERATURES SHLD BE IN KELVIN.

NOT TOO SURE IF IT'S CORRECT BUT TRY IT OUT TO SEE IF U GET A REASONABLE ANSWER.