Answer:
a) There must be added 4.465 grams of aspirin
b) The unknown has a molecular weight of 342.2 g/mol
Step-by-step explanation:
Step 1: Data given
The vapor pressure of chloroform is 173.11 mm Hg at 25°C
a nonvolatile, nonelectrolyte (MW = 180.1 g/mol), must be added
Mass of chloroform = 244.0 grams
The vapor pressure is reduced to 171.05 mm Hg
chloroform = CHCl3 = 119.40 g/mol.
The boiling point of water, H2O, is 100.000 °C
Step 2: Calculate moles chloroform
244.0g CHCl3/ 119.40g/ mol = 2.0436 mol CHCl3
step 3: Calculate moles aspirin
Moles aspirin = x grams / 180.1 g/mol
(p0 - p)/p0
⇒ p0 is the initial pressure = 173.11 mm Hg
⇒ p = the reduced pressure = 171.05 mm Hg
(p0 - p)/p0 = (173.11-171.05)/173.11 = (xg/180.1 g/mol) / (2.0436 mol + (xg/180.1g/mol))
0.0119 mol = (xg/180.1 g/mol) / (2.0436 mol + (xg/180.1g/mol))
0.02432 + (0.0119x/180.1) = (x/180.1)
0.02432 =(( x - 0.0119x)/180.1)
0.9981x = 4.38
x = 4.465 grams
There must be added 4.465 grams of aspirin
b) What is the molecular weight they determined for this compound?
Step 1: Define molar mass of the compound:
Molar mass = mass / moles
Molar mass compound = 11.55 grams / moles
Step 2: Calculate ΔT
ΔT = Tsoln - Tpure
ΔT = 100.071 - 100.00 = 0.071 °C
Step 3: Calculate m
ΔT = m*Kb
0.071°C = m*0.512 °C/m
m = 0.071 °C / 0.512 °C/m
m = 0.13867 m = 0.13867 mol/kg
Step 4: Calculate number of moles of the compound
Moles = mass of water * m
Moles = 0.2434 kg * 0.13867 mol/kg
Moles = 0.03375 moles
Step 5: Calculate molar mass
Molar mass = mass / moles
Molar mass compound = 11.55 grams / 0.03375 moles
Molar mass compound = 342.2 g/mol
The unknown has a molecular weight of 342.2 g/mol (and can be sucrose. It has a molar mas of 342.2 g/mol, is nonvolatile and non-electrolyte.).