Assuming ideal-gas behavior, how many grams of ammonia are in the flask?

Question

A 3.00-L flask is filled with gaseous ammonia, NH_3. The gas pressure measured at 23.0 degrees C is 1.55 atm.

Answer 1

Just plug the values you have into the ideal gas law equation. Remember that temperature needs to be converted from C to Kelvin:

PV = n RT
(1.55 atm )(3.00 L) = n (.0821 Latm/molK) (23+273 K)

and solve for n. This will give you the number of moles of ammonia. To calculate grams, multiply the moles of ammonia by the molar mass of NH3 and you've got it.