Chapter 16 Solutions (abbr. “soln”)

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Chapter 14: Solutions
Concentration formulas
Making a solution
Freezing pt. depression
Boiling pt. elevation
Ch. 14
Concentration formulas
Molarity
Molality
Equation
M = mole of solute . m = mole of solute .
Liter of solution
kilogram of solvent
Effects
Depends on temp.
Does not depend on temp.
How do you make a solution?
• Solvation: process of surrounding solute
particles with solvent particles to form a
solution
• Heat of solution: overall energy change
that occurs during the solution formation
process
Speed of dissolving
• Solution formation depends on how much
solute will dissolve in solvent.
Affect on dissolving
Stirring/
1
agitation
Stir/agitate  Solute dissolves faster
Increase temp  Solute dissolves
2 Temperature faster
Surface area
3
of solute
Increase surface area  Solute
dissolves faster
Surface area
Solubility – amount of solute that
dissolves in solvent at a given temp.
and pressure
Varying solubility of solution
1
Unsaturated
solution
Less solute than
saturated solution
2
Saturated
Solution
Contains maximum
amount of solute at
given temp and pressure
3
Supersaturated
solution
Contains more solute than it
can theoretically hold at
given temp. and pressure
Factors affecting solubility
Simulation: Solubility and temp
Factors affecting solubility
•Increase temp
• increase solubility of solids
Temper1
ature
•Allows supersaturated soln. to
be made
• decrease solubility of gases
•Crystallization of supersaturated
soln. initiated by
•seed crystal
•If container is scratched
Factors affecting solubility
Factors affecting solubility
•Negligible for
solubility of L and S
2 Pressure •Increase pressure
gas  increase
solubility gas
•(Henry’s Law)
Section 2
Concentrations of Solutions
Objective:
Using Molarity (M)
Change to
moles!!
1. Mass of solute in grams
2. Amount of solute in mol
3. Volume of solute in L
4. Molar concentration, M
1. What is the molarity of a solution prepared by
dissolving 37.94 g of potassium hydroxide in some
water and then diluting the solution to a volume of
500.0 mL?
Don’t
Given:
Unknown:
forget to
use moles!
2. Determine the molarity of a solution prepared by
dissolving 141.6 g of citric acid, C3H5O(COOH)3 in water
and then diluting the resulting solution to 3500.0 mL.
Given:
Unknown:
3. What is the molarity of a salt solution
made by dissolving 280.0 mg of NaCl in
2.00 mL of water?
Given:
Unknown:
mg…
tricky?
How do
you get
grams?
Here’s a hint:
1g = 1000 mg
4. What is the molarity of a solution that contains
390.0 g of acetic acid, HC2H3O2, dissolved in
enough acetone to make 1000.0 mL of solution?
Given:
Unknown:
5. An analytical chemist wants to make 750.0 mL of a
6.00 M solution of sodium hydroxide. What mass of
NaOH will the chemist need to make this solution?
Given:
Unknown:
6. What mass of glucose, C6H12O6
would be required to prepare
5.000x103 L of a 0.215 M solution?
Given:
Unknown:
Can you
figure
this
out?
7. A solution has a volume of 2.0 L and contains 36.0
g of glucose (C6H12O6). If the molar mass of glucose is
180 g/mol. What is the molarity of the solution?
Given:
Unknown:
8. A solution has a volume of 250 mL and
contains 0.70 mol NaCl. What is its molarity?
Given:
Unknown:
This
is
CAKE
!
Section 3: Colligative properties
• Property that depends on amount of solute
in solution, and not on identity of solution.
Freezing point (FP)
• Solute disrupts formation of orderly pattern; as a
result, more kinetic energy must be withdrawn from
a solution to cause solidification.
* Solution that contains a solute has a lower
Freezing point than the pure solvent
Boiling point (BP)
• Since adding a solute to a solvent decreases VP,
additional kinetic energy must be added to raise
VP and initiate boiling.
* Solution that contains a solute has a higher
boiling point than the pure solvent
Factors affecting Colligative Properties
1. Increase amt. of solute, increase
magnitude…
a. VP lowering
b. FP depression
~1 mol solute lowers FP by 1.86°C
c. BP elevation
~ 1 mole solute increases BP by 0.512°C
Factors affecting Colligative Properties
2. Solutes that dissociate have greater
effects than nondissociating (nonpolar)
solutes
3 particles
Affect colligative
property least
6 particles
9 particles
Affect colligative
property most
Calculations with Colligative properties
• Freezing pt. depression (FP dep)
– difference in temperature between FP of
solution and FP of pure solvent
ΔTf = (Kf)(m)
FP dep. example problems
FP dep example 1: What is the freezing point
depression (ΔTf) of a 0.100 m solution made
with water?
ΔTf = (Kf)(m)
FP dep. Example 2: A solution made with ethanol is
made to lower the freezing point by 6.10˚C. What is
the molality of the solution?
ΔTf = (Kf)(m)
Calculations with Colligative properties
• Boiling point elevation (BP elev.)
– difference in temp between BP of a solution
and BP of pure solvent
ΔTb = (Kb)(m)
BP dep. example problems
BP elev. Example 1: What molality of NaCl
solution would have to be used raise the boiling
point of water by 2.00˚C?
ΔTb = (Kb)(m)
BP elev. Example 2: Determine BP elevation (ΔTb)
of a 0.857 m CaCl2 solution?
ΔTb = (Kb)(m)
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