Ideal Gas Law: Calculate Moles and Mass

Question

A sample of nitrogen gas collected at a pressure of 0.936 atm and a temperature of 298 K is found to occupy a volume of 833 milliliters. How many moles of N₂ gas are in the sample?  ________mol

Answer 1

Hello Omar. Happy to help.

The ideal gas law says Pressure, Temperature and Volume of the gas are related to each other. The ideal gas law states PV= nRT. Where n is the number of moles,

R is the Universal gas constant R=0.08206L atm/(K mol)

We need to find the number of moles.

You have P=0.936 atm, T= 298 K and volume =833mL

First you want to make sure all of your units are consistent with the molar mass constant so your units will cancel. We have mL and we need L. All the others are good. So 833 mL is 0.833 L.

Now plug the values into the equation PV=nRT. Since we need moles (n) we can divide both sides by RT to get n=PV/RT.

This gives n= ( 0.936atm) (0.833 L) / (0.08206L atm/(K mol)) (298K)

n=0.0319 moles

Hope this helps.

Answer 2

Hello Omar,

To solve this problem, start by identifying the knowns and unknowns given in the problem. Then you will use the ideal gas law, PV=nRT to solve for the unknown (in this case "n" the number of moles of N₂ gas). It is sometimes helpful to also identify which values need to be converted before starting as well!

P= 0.936 atm

V= 833 mL ⇒ convert to L so that the units will properly cancel with those in the ideal gas constant R

n= ?

R= ideal gas constant= 0.0821 L·atm/K·mol

T= 298 K

I also find it easier to re-arrange the ideal gas law equation *before* inserting all the numerical values. To get n by itself, we will need to divide both sides by "RT".

n=PV/RT

Now you are ready to plug in the numerical values and solve for n (remember to use a parenthesis when entering the denominator into your calculator!).

Hope that helps get you started! I'd be happy to work with you on these types of problems during a private tutoring session :)