Quick Review
1) What is the % water in
iron (II) sulfate heptahydrate?
2) What is the extent of hydration
of aluminum sulfate if the
crystal is 48.67% water?
Solutions
--don’t worry—we’ll have
problems to go with them.
How does a solute dissolve in a
solvent?
How does a solute dissolve in a
solvent?
• IM forces in mixture are strong enough
overcome IM forces in solute
How much of a solute will dissolve
in a solvent?
How much of a solute will dissolve
in a solvent?
• It depends on the solute and the solvent
--some things, not much (e.g. Ag2S/H2O)
--others, any proportions, recall: “Miscible”
(N2/O2 ,for example)
Answer: Its “solubility”
How much of a solute will dissolve
in a solvent?
Solid/H2O: usually increases at higher To
• _____ gsolute/100 gsolvent
Gas/H2O: very low solubilities in water
--solubilities decrease with To
--solubilities increase directly with P
(Henry’s Law)
How can you speed up dissolving?
How can you speed up dissolving?
1)
2)
3)
4)
Raise the temperature of the solvent
Stir or shake
Grind or crush a solid
Add more solvent
Why do these methods help?
Why do these methods help?
Grind or crush a solid —increases surface
area—more solute is in contact with
solvent
Raise the temperature —particles move
faster—more collisions & more effective
collisions
Stir or shake, or add more solvent —brings
fresh solvent into contact with solute
How can you express
concentration?
How can you express
concentration?
1)
2)
3)
4)
5)
Mass % composition
Molarity
Molality
Mole fraction
Density
Dilution and titration problems
V x M= Moles
• Moles of solute in new solution = moles in
the stock solution. Molarity goes down,
volume goes up
• Moles of H+ and OH- are equal. The more
concentrated solution requires less volume
Dilution problems
Before
After
V1 x M1 =
_____moles
V2 x M2 =
_____moles
moles before = moles after
Small volume,
high concentration

Larger volume,
lower concentration
Dilution problems
• 10.00 ml of 1.53 M NaCl is diluted to 250. ml.
What is the new concentration?
• 15 ml of 18 M H2SO4 is diluted to 200. ml. What
is the new concentration?
• I need 50.00 ml of a 1.20 M NaCl solution. What
volume of a 3.00 M stock solution will I need to
add to the flask before diluting to 50.00 ml?
• I need .050 M HCl. If I start with 30. ml of 3.0 M
HCl, what volume of the new solution can I
make?
Neutralization problems
Acid
Base
V1 x M1 =
_____moles
moles H+
Moles you know
V2 x M2 =
_____moles
= moles OH-

Concentration
you’re measuring
Titration problems
• 10.00 ml of .153 M NaOH is titrated with 25.0 ml.
HCl. What is the concentration of the acid?
• 15.00 ml of .1877 M H2SO4 is titrated with 21.22
ml NaOH. What is the concentration of the base?
• 5.00 ml of a 1.20 M NaOH solution is titrated with
.300 M HCl. What volume will be required?
Quick Review
1) 12 g NaCl is dissolved in 150 g H2O.
What is the % comp, molality and mole
fraction?
2) 15 g NaCl is dissolved to make 250 ml of
solution.
What is the molarity?
The relationship between M and m
• We measured masses and volumes and
were able to calculate M, m, and D.
• Use two of these to calculate the third.
For example:
1. What is the molality of a .980 M AlCl3
(FM=133.34 g/mol) solution? (D=1.089 g/ml
=1089 g/L)
2. What is the molarity of a 1.000 m HC2H3O2
(FM=60.05 g/mol) solution? (D=1.064 g/ml
=1064 g/L)
3. What is the density of a 1.19 M CaCl2
(FM=110.99 g/mol) solution, if the molality
is 1.23 m?
Colligative properties
• Solutes affect the physical properties of a
solution.
• If the effect is caused by the number of
solute particles, it’s a colligative property
Colligative properties include…
•
•
•
•
Freezing point depression
Boiling point elevation
Vapor pressure depression
Osmotic pressure
Freezing point depression
DTf=iKfm
• If you dissolve a solute, the solution has a
lower freezing point than the pure solvent
• The effect is directly related to the number
of particles
• Kf for water is 1.86oC/m
Freezing point depression
•
•
•
•
DTf=iKfm
The constant, Kf, is specific to the solvent,
Kf =1.86oC/m , for water
The new freezing point is FP’=FP-DTf
i is the van’t Hoff factor —the moles of
particles/mole of solute. Ionic compounds
dissociate (i=2,3,etc), non-electrolytes
don’t (i=1)
m is molality (moles solute/ kg solvent)
FP depression problems:
1. What is the freezing point of a .86 m glucose
solution (i=1)?
2. How about a .86 m NaCl solution (i=?) ?
3. What is the freezing point of 1.83 g C2H4(OH)2
dissolved in 15 g H2O? (i=1)
4. What is the freezing point of a solution of 4.9 g
CCl4 dissolved in 33 g benzene?
5. What is the formula mass of a non-electrolyte
solute if 12 g dissolved in 48 g H2O gives a FP
of -1.2oC?
Boiling point elevation
• Same issues
DTb=iKbm
Kb for water =.51 oC/m
BP elevation problems:
1. What is the boiling point of a .86 m glucose
solution (i=1) ?
2. How about a .86 m NaCl solution (i=?) ?
3. What is the boiling point of 1.83 g C2H4(OH)2
dissolved in 15 g H2O? (i=1)
4. What is the boiling point of a solution of 4.9 g
CCl4 dissolved in 33 g benzene?
5. What is the formula mass of a non-electrolyte
solute if 12 g dissolved in 48 g H2O gives a BP
of 103.2oC?
Vapor pressure depression
• Nonvolatile solutevapor pressure ↓
• This causes the boiling point elevation. Vapor
pressure = outside pressure at BP!
• Use a mole fraction for a direct relationship
• If the solute can vaporize—both components
add to the vapor pressure.
VP H O = 760 mmHg at 100oC!
2
1. What is the VP, at 100oC, of the solution
of 12g C2H4(OH)2 dissolved in 150 g
H2O?
2. What is the VP, at 100oC, of the solution
of 12g NaCl dissolved in 150 g H2O?
3. What is the VP, at 35oC, of the solution
of 120 g C2H5OH in 150 g H2O?
VP’s at 35oC: C2H5OH:101 mmHg
H2O:
42 mmHg
Osmotic pressure
• Used in biology, osmosis is the diffusion of
water across a membrane
P=-iMRT
• P is the osmotic pressure
• i is the van’t Hoff factor
• M is the molarity of the solution
• R is the ideal gas constant
• T is the absolute temperature
• What is the osmotic pressure of .15M
NaCl?
• What is the osmotic pressure of pure
water?
Non-Electrolytes Electrolytes
•
•
•
•
Molecular
Do not dissociate
i=1
Don’t conduct
electricity in
solution
• Raise BP
• Lower FP, VP
•
•
•
•
Ionic (&strong acids)
Dissociate into ions
i>1
Conduct electricity in
solution
• Raise BP more
• Lower FP, VP more