Question

Using molar volume (stp) or the ideal gas law equation, determine the molar mass , g/mole, of each of the fillowin g.

1- 12.5 g of a gas that has a volume of 2.25 L at stp M =

2- 0.742 g of a gas that has a volume of 835 ml at 1.10 ATM and 19 degrees C. M=

Answer 1

1) Answer:

weight = 12.5 g, Volume = 2.25 L at STP conditions

PV =nRT

n = number of moles

n = weight / molar mass

At STP conditions,

P = 1 atm, R = 0.0821 L atm K^-1mole^-1;  T = 273 K

PV =nRT

1 x 2.25 = (12.5/molar mass) x 0.0821 x 273

molar mass = (12.5/2.25) x 0.0821 x 273

molar mass = 124.518 g/mole

2) Answer:

weight = 0.742 g, Volume = 835 mL = 0.835 L

T = 19 C = 19+273 K = 292K; P = 1.10 atm

PV =nRT

n = number of moles

n = weight / molar mass

PV =nRT

1.10 x 0.835 = (0.742/molar mass) x 0.0821 x 292

0.9185 = (0.742/molar mass) x 0.0821 x 292

molar mass = (0.742/0.9185) x 23.9732

molar mass = 19.366 g/mole