What is the molecular mass of a gas whose density is 1.25 grams per liter at STP?

STP = standard temperature and pressure

Use the formula:

d = MP/RT

where:

d = density = 1.25 g/L

M = molar mass (unknown)

P = pressure = 1 atm (standard pressure)

R = universal gas constant = 0.8206 L*atm/mol*K

T = temperature = 0C or 293.15 K (standard temperature)

1.25 g/L = M*(1 atm)/(0.08206 L*atm/mol*K)*(273.15 K)

M = 28.0 grams/mol