Question

Trichloroethane, C2H3CL3 is used as a degreaser (solvent for waxes and oils). Its density is 1.435 g/mL and its vapor pressure at 20 degrees C is 124 mmHg.

a) How many mL will vaporize in an evacuated 1.50-L flask at 20 degrees C?

b)A 3.00-mL sample is poured into an evacuated 1.5-L flask at 20 degrees C. Will all the liquid vaporize? If not, what is the pressure in the flask?

c) A similar 3.00-mL sample is poured into an evacuated 20.00-L flask at 20 degrees C. What physical state(s) is/are in the flask?

Answer 1

The density of trichlorethane = 1.435 g / mL

Vapour pressure at 20 degree C = 124 mmHg

a) let us calcualte moles of trichloromethane from ideal gas equation

PV = nRT

Pressure = 124mmHg

V = 1.5 L

n = moles = ?

Temperature = 293 K

R =

62.36 L mmHg /K /mole

So number of moles = n = PV / RT = 124 X 1.5 / 62.36 X 293 = 0.0101 moles

So mass of trichloromethane = Moles X molecular weight = 0.0101 X 133 = 1.34 grams

So volume = Mass / density = 1.34 / 1.435 = 0.935 mL

b) The whole amount will not vapouirze onlu 0.935 mL will vapourize

c) Let us calculate the moles in 20L of flask

Moles = PV / RT = 124 X 20 / 62.36 X 293 = 0.135

So mass = Moles X molecular weight = 0.135 X 133 = 17.95 grams

So volume = Mass / density = 17.95 / 1.435 = 12.5 mL

So whole trichloroethane will evaporate.