Chemistry 16.4
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16.4
Calculations Involving Colligative Properties
Cooking instructions often
call for the addition of a
small amount of salt to the
cooking water. Dissolved
salt elevates the boiling
point of water. You will
learn how to calculate the
amount the boiling point of
the cooking water rises.
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
Molality and Mole Fraction
What are two ways of expressing the
concentration of a solution?
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
The unit molality and mole fractions are
two additional ways in which chemists
express the concentration of a solution.
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
The unit molality (m) is the number of moles of
solute dissolved in 1 kilogram (1000 g) of
solvent. Molality is also known as molal
concentration.
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
To make a 0.500m
solution of NaCl, use a
balance to measure
1.000 kg of water and
add 0.500 mol (29.3 g)
of NaCl.
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
Ethlylene Glycol (EG) is added to water as
antifreeze.
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SAMPLE PROBLEM 16.6
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SAMPLE PROBLEM 16.6
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SAMPLE PROBLEM 16.6
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SAMPLE PROBLEM 16.6
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Practice Problems for Sample Problem 16.6
Practice ProblemsFor Sample Problem 16.6
Problem Solving 16.29 Solve
Problem 29 with the help of an
interactive guided tutorial.
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
The mole fraction of a solute in a solution is the
ratio of the moles of that solute to the total
number of moles of solvent and solute.
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16.4
Calculations Involving
Colligative Properties
>
Molality and Mole Fraction
In a solution containing nA mol of solute A and nB
mol of solvent B (XB), the mole fraction of solute
A (XA) and the mole fraction of solvent B (XB) can
be expressed as follows.
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SAMPLE PROBLEM 16.7
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SAMPLE PROBLEM 16.7
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SAMPLE PROBLEM 16.7
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SAMPLE PROBLEM 16.7
Sample Problem 16.7
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Practice Problems for Practice Problem 16.7
Problem Solving 16.32 Solve
Problem 32 with the help of an
interactive guided tutorial.
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression and
Boiling-Point Elevation
Freezing-Point Depression and BoilingPoint Elevation
How are freezing-point depression and
boiling-point elevation related to
molality?
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
The magnitudes of the freezing-point
depression
and the boiling-point
elevation
of a solution are directly
proportional to the molal concentration
(m), when the solute is molecular, not
ionic.
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
The constant, Kf, is the molal freezing-point
depression constant, which is equal to the
change in freezing point for a 1-molal solution of
a nonvolatile molecular solute.
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
The constant, Kb, is the molal boiling-point
elevation constant, which is equal to the
change in boiling point for a 1-molal solution of a
nonvolatile molecular solute.
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
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Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
Simulation 21 Discover the principle
underlying the colligative properties of
solutions.
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16.4
Calculations Involving
Colligative Properties
>
Freezing-Point Depression
and Boiling-Point Elevation
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SAMPLE PROBLEM 16.8
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SAMPLE PROBLEM 16.8
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SAMPLE PROBLEM 16.8
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SAMPLE PROBLEM 16.8
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Practice Problems for Sample Problem 16.8
Problem Solving 16.33 Solve
Problem 33 with the help of an
interactive guided tutorial.
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SAMPLE PROBLEM 16.9
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SAMPLE PROBLEM 16.9
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SAMPLE PROBLEM 16.9
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SAMPLE PROBLEM 16.9
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Practice Problems for Sample Problem 16.9
Problem Solving 16.36 Solve
Problem 36 with the help of an
interactive guided tutorial.
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16.4 Section Quiz.
Assess students’ understanding
of the concepts in Section 16.4.
Continue to:
-or-
Launch:
Section Quiz
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16.4 Section Quiz.
1. What is the mole fraction of He in a gaseous
solution containing 4.0 g of He, 6.5 g of Ar,
and 10.0 g of Ne?
a. 0.60
b. 1.5
c. 0.20
d. 0.11
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16.4 Section Quiz.
2. The freezing point depression caused by a
given concentration of a nonvolatile molecular
solute
a. depends on the solute.
b. depends on the solvent.
c. is always the same.
d. cannot be determined.
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16.4 Section Quiz.
3. What are the freezing and boiling points of a
0.1m solution of CaCl2 in water?
a. -0.2°C, 100.1°C
b. -0.6°C, 100.1°C
c. -0.6°C, 100.2°C
d. -0.6°C, 99.8°C
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16.4 Section Quiz.
4. Compared to the freezing point depression by
ethylene glycol (C2H6O2,) for a given solvent,
the freezing point depression caused by the
same molal concentration of CaCl2 would be
a. exactly the same.
b. twice as large.
c. three times as large.
d. four times as large
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