Mass of Substance = Volume of Substance x Density of Substance
Density of cyclopentane = 745.4 kg/m3
Density of cyclopentane in pound/litre = 0.0007453999999999999
Mass of a Substance = 0.0007453999999999999 x 7
7 litre of cyclopentane weighs 0.005217799999999999 pound