Question

The density of a gas at S.T.P is 1.25g/dm³. Calculate the molecular mass of gas​

Answer 1

Answer:

For ideal gas

PV=RT

V=RT/P

Density is given by

D=M/V

Where

M - mass

V - volume

Putting the value of V

D= M / ( RT/P )

D = PM / RT

Hence,

D = PM/RT

1.25 = 1 atm x M/ (0.0821 x 273)

M = 28 g/mol

Explanation :

One mole of gas at STP would occupy 22.4 liters, this gas is 1.25 g/liter so in 22.4 virtual liters it will have a mass of 28 grams, so the MW= 28g/mol and the gas is N2.