Question

A 3.00-l flask is filled with gaseous ammonia, nh3. the gas pressure measured at 28.0 ∘c is 1.75 atm . assuming ideal gas behavior, how many grams of ammonia are in the flask?

Answer 1

I have found this variation on the ideal gas equation to be very handy. 
PV = nRT ..... n = m / M.... where m is mass, M is molar mass 
PV = mRT / M 
m = PVM / RT
m = 1.75 atm x 3.00L x 28.0g/mol / 0.0821 Latm/molK / 295K 
m = 6.07g

The grams of ammonia are in the flash is a total of 6.07 grams