molar mass of gas X... pls help

matthew77ask

the mass of a 250cm3 round bottomed flask is filled with gas X is determined to be 16.2850g. the mass of the empty flask and stopper is 15.9516g. what is the molar mass of gas X?

am i right to do it this way:

mass of gas X alone = 16.2850 - 15.9516 = 0.3334g
volume of gas X = 250/1000 = 0.25 dm3

molar mass of gas X = 0.3334/0.25 = 1.3336g/dm3

however, the answer is 32g, where did i make a mistake?

thank you

Stevedye56

what conditions are you working under?? STP?

molar mass= g/mol
not g/L

If its at room temp then you have:
295K
1 atm
24.2 L/mol

.250L/(24.2L/mol)= .01033mol

.3334g/.01033mol= 34g/mol

matthew77ask

working under rtp

thank you