A gas sample weighing 0.528 g is collected in a flask having a volume
of 126 mL.
At 75 degrees C the pressure of the gas is 754 torr. The molecular
mass of the gas is closest to which one of the following?
a. 120
b. 140
c. 160 
d. 180

Hi teatea!!

Recall the answer to the question #227688.

P.V = n.R.T  
 
Then: 
 
n = P.V / R.T 
 
We have for this problem: 

P = 754 torr = 0.9921 atm 
V = 126 mL = 0.126 L 
T = (75+273)K = 348K 
R = 0.082058 atm/(mol * K) 
 
n = (0.9921 atm x 0.126 L) / (0.082058 atm/(mol * K) x 348K) = 0.0043775 mol
  
There are 0.0043775 moles of gas. 

Molecular Mass  in grams = 0.528g x 1mol/ 0.0043775 mol = 120.62g

Then the correct answer is a.

Hope this helps.

livioflores-ga