Question

Compute the approximate density of acetylene, C2H2, at 25 degrees C and 0.98 atm.

Answer 1

We know that PV = nRT

                             = ( m/M ) RT

                         P = ( m/V ) x ( RT / M )

                         P = dRT /M

Where

d = density = ? (in g/mL)

T = Temperature = 25 ^oC = 25+273 = 298K

P = pressure = 0.98 atm

M = Molar mass of C₂H₂ = ( 2xAt.mass of C ) +(2x At.mass of H )

                                        = ( 2x12 ) + (2x1)

                                        = 26 g/mol

R = gas constant = 0.0821 L. atm / (mol - K)

m = mass of the gas

V= Volume of the gas

Plug the values we get   d = PM / RT

                                          = ( 0.98 x 26 ) / ( 0.0821 x 298 )

                                          = 1.04 g/mL

Therefore the density of acetylene is 1.04 g/ml