calculate the boilinng point (at 1 atm) of a solution containing 116g of acetone
ID: 2997482 • Letter: C
Question
calculate the boilinng point (at 1 atm) of a solution containing 116g of acetone MW58 and 72g of water(MW=18) by using the following table assume that this mixture obeys Raoults law
T vapor pressure (atm) Acetone Vapor pressure (atm) water
60 1.14 0.198
70 1.58 0.312
80 2.12 0.456
90 2.81 0.694
Explanation / Answer
Calculate the boiling point (at 1 atm) of a solution containing 116 g of acetone (Mw = 58) and 72 g of water (Mw = 18) by using the following table:
Temperature
oC
Vapor pressure (atm)
Acetone
Vapor pressure (atm)
Water
60
1.14
0.198
70
1.58
0.312
80
2.12
0.456
90
2.81
0.694
A liquid starts to boil when its vapor pressure matches the atmospheric pressure (1 atm in this case). Thus, according to Raoult's law
P = xacetone Poacetone + xwater Powater = 1 atm
From the given data we can calculate the molar fractions
molesacetone = 116/58 = 2
moleswater = 72/18 = 4
total moles = 6
xacetone = 2/4 = 1/3
xwater = 4/6 = 2/3
thus
P = 2/3 Poacetone + 1/3 Powater= 1 atm
By trials, using the table, we can find the values of vapor pressure which satisfies the above equation. The best result is obtained by using the values at 80oC :
P = 2/3 0.456 + 1/3 2.12 = 1.01 atm
then the boiling point is about 80oC.
Temperature
oC
Vapor pressure (atm)
Acetone
Vapor pressure (atm)
Water
60
1.14
0.198
70
1.58
0.312
80
2.12
0.456
90
2.81
0.694