Question

1. The effect of chlorofluorocarbons (such as CCl₂F₂(g)) on the depletion of the ozone layer is well known. The use of substitutes, such as CH₃CH₂F(g), for the chlorofluorocarbons, has largely corrected the problem. Calculate the volume (in L) occupied by 17.5 g of each of these compounds at STP.

- CCl₂F₂(g)

- CH₃CH₂F(g)

2. Calculate the density (in g/L) of Freon-12, CF₂Cl₂, at 28.6°C and 0.984 atm.

Answer 1

1.

Mass of CCl₂F₂ = 17.5 g

Molar mass of CCl₂F₂ = 120.91 g/mol

Moles of CCl₂F₂ = mass of CCl₂F₂ / molar mass of CCl₂F₂

                           = 17.5 g / 120.91 g/mol

                           = 0.145 mol

At STP, 1 mol of any gas occupies 22.4 L

Therefore, at STP, 0.145 mol of CCl₂F₂ occupies = (22.4 L/1 mol) x 0.145 mol

                                                                               = 3.25 L

Hence, volume (in L) occupied by 17.5 g of CCl₂F₂ at STP = 3.25 L

-

Mass of CH₃CH₂F = 17.5 g

Molar mass of CH₃CH₂F = 48.06 g/mol

Moles of CH₃CH₂F = mass of CH₃CH₂F / molar mass of CH₃CH₂F

                               = 17.5 g / 48.06 g/mol

                               = 0.364 mol

At STP, 1 mol of any gas occupies 22.4 L

Therefore, at STP, 0.364 mol of CH₃CH₂F occupies = (22.4 L/1 mol) x 0.364 mol

                                                                                   = 8.15 L

Hence, volume (in L) occupied by 17.5 g of CH₃CH₂F at STP = 8.15 L