# Question 52ffd

Mar 11, 2015

You use the ideal gas law equation, $P V = n R T$, to figure out how many moles of gas you have, then, asssuming you know the identity of the gas, you use its molar mass to see how many grams you have.

In your case, the number of moles will be

$P V = n R T \implies n = \frac{P V}{R T}$

n = (668/760"atm" * "2.15 L")/(0.082("atm" * "L")/("mol" * "K") * "298 K") = "0.0773 moles"#

Since the number of moles can be written as mass divided by molar mass, you'd get

$n = \frac{m}{M} _ M \implies m = n \cdot {M}_{M}$

SIDE NOTE Notice that I've converted the pressure from torr or mmHG, whichever you had, to atm to be able to use the value of 0.082 for R, since it's expressed in atm L/mol K.