A 0.465 g sample of an unknown compound occupies 245 mL at 298 K and 1.22 atm. What is the molar mass of the unknown compound? A. 38.0 g/mol
B. 56.0 g/mol
C. 12.2 g/mol
D. 33.9 g/mol
E. 81.8 g/mol
Solution: Molar mass has units of grams/moles. Therefore, if we have grams and divide them by moles, we will get molar mass. Grams are given and we need to find moles. We are given:
V = 245 mL = 0.245L
T = 298 K
P = 1.22 atm
We can use the Ideal Gas Law to find the number of moles:
PV=nRT
1.22 atm*0.245L = n (0.0821 Latm/molK)(298 K)
n = 0.0122 moles
Now, lets find the molar mass.
Molar mass = 0.465 g/0.0122moles = 38.0 Choice A