Version 348 – Quiz 1 – laude – (51155) 1
This print-out should have 8 questions.
Multiple-choice questions may continue on
the next column or page – find all choices
before answering.
001 5.0 points
An unknown liquid has a vapor pressure of
88 mmHg at 45 ◦C and 39 mmHg at 25 ◦C.
What is its heat of vaporization?
1. 32 kJ/mol correct
2. 32000 kJ/mol
3. 2000 J/mol
4. 2000 kJ/mol
Explanation:
Use the Clausius-Clapeyron Equation.
Here, the only thing we don’t know is ∆Hvap.
ln(P2
P1
) = ∆Hvap
R(1
T1
−1
T2
)
∆Hvap =Rln(P2/P1)
1/T1−1/T2
∆Hvap = 32.0 kJ/mol
002 5.0 points
If ethylene glycol has a pure vapor pressure
of 28 torr and acetaldehyde has a pure vapor
pressure of 756 torr A mixture of 24 moles of
ethylene glycol and 8 moles of acetaldehyde
would have what total vapor pressure?
1. 189 torr
2. 21 torr
3. 588 torr
4. 196 torr
5. 210 torr correct
Explanation:
Ptotal =χa·Pa+χb·Pb+...
Ptotal = 0.75 ·28 torr + 0.25 ·756 torr
Ptotal = 210 torr
003 5.0 points
Which of the following is not related to
colligative properties?
1. Applying a pressure across a semi-
permeable membrane to force pure water
across.
2. Mixing water and anti-freeze to improve
radiator fluid’s freezing/boiling point.
3. Adding lots of salt to ice to lower its
freezing point when making ice cream.
4. Water boiling at 75 ◦Cinstead of 100 ◦C
high in the Himalayan mountains. correct
Explanation:
The change in boiling point as one’s ele-
vation changes is not a consequence of col-
ligative properties, but rather of the changing
atmospheric pressure.
004 5.0 points
How much heat is required to heat 0.1 g of
ice at −30 ◦C to steam at 100 ◦C? Use the ap-
proximate values below for your calculation.
cice = 2 J/g·◦C
csteam = 2 J/g·◦C
cwater = 4 J/g·◦C
∆Hvap = 2,260 J/g
∆Hfus = 340 J/g
1. 193 J
2. 187 J
3. 306 J correct
4. 80 J
5. 300 J
6. 74 J
