The common laboratory solvent chloroform is often used to purify substances diss
ID: 941435 • Letter: T
Question
The common laboratory solvent chloroform is often used to purify substances dissolved in it. The vapor pressure of chloroform , CHCl3, is 173.11 mm Hg at 25 °C.
In a laboratory experiment, students synthesized a new compound and found that when 14.88 grams of the compound were dissolved in 230.8 grams of chloroform, the vapor pressure of the solution was 168.61 mm Hg. The compound was also found to be nonvolatile and a non-electrolyte.
What is the molecular weight of this compound?
chloroform = CHCl3 = 119.40 g/mol.
NOTE : This proplem related to Raoult's Law
Explanation / Answer
m = 14.88 sample
m = 230.8 g of Chloroform
P° = 168.61 mm Hg
since it is nonvolatile then
dP = xsolute * P°solvent
Pmix = P°solvent - dP
then
substitute all values
Pmix = P°solvent - xsolute * P°solvent
Pmix = (1-xsolute) * P°solvent
168.61 = (1-x) * (173.11)
x = -(168.61 /173.11-1)
x = 0.02599503206
x S= mol of S/ (mol of S + mol of solvent)
mol of solvnet = mas/MW = 230.8/119.4 = 1.9329983
0.02599503206 = (mol of S)/(mol of S + 1.9329983)
(mol of S + 1.9329983) = 1/(0.02599503206 ) * mol of S
(mol of S + 1.9329983) = 38.46 mol of S
-37.46 mol of S = -1.9329983
mol of S= 1.9329983/(37.46) =0.0516016631 mol
then
MW of sample = mass of sample / mol of sample = 14.88/0.0516016631 = 288.362 g /mol