# You have 1.25 L of oxygen gas at STP. What is its mass?

##### 1 Answer

Jun 19, 2016

#### Explanation:

We are at STP and that means we have to use the ideal gas law equation!

- P represents pressure (could have units of atm, depending on the units of the universal gas constant)
- V represents volume (must have units of liters)
- n represents the number of moles
- R is the universal gas constant (has units of
#(Lxxatm)/ (molxxK)# ) - T represents the temperature, which must be in Kelvins.

Next, list your known and unknown variables. Our only unknown is the number of moles of

At STP, the temperature is 273K and the pressure is 1 atm. The proportionality constant, R, is equal to 0.0821

Now we have to rearrange the equation to solve for n:

To get the mass of