The density of a certain gas at 27.0°C and 98.66 kPa is 2.53 g/L. Calculate the molecular mass.?

Density, d = 2.53 g/L
Temperature,. T = (273.2 + 27.0)°C = 300.2 K
Pressure = 98.66 kPa
Gas constant, R = 8.314 J / (mol K)
Molar mass, M = ? g/mol

PV = nRT and n = m/M
PV = (m/M)RT
M = (m/V)RT/P
Hence, M = dRT/P

Molar mass, M = 2.53 × 8.314 × 300.3 / 98.66 g/mol = 64.0 g/mol (to 3 sig. fig.)

Assume you have 1 liter of this gas. Now, use the ideal gas law for find the number of moles (n) you have. I will convert kPa to atm so as to use R = 0.0821 L-atm/K-mole. 98.66 kPa x 1 atm/101.3 kPa = 0.974 atm. Also convert ºC to K; 27.0ºC + 273 = 300K
PV = nRT
n = PV/RT
n = (0.974 atm)(1 L)/(0.0821 L-atm/K-mol)(300K)
n = 0.0395 moles
Since molecular mass is g/mole, we have 2.53 g/0.0395 moles = 64.1 g/mole = molecular mass