1. Solutions
Chapter 15

2. What Are Solutions?
Section 15.1

3. What Are Solutions?
Solution: homogeneous mixture of 2 or more substances
Solid, liquid, or gas
Solvent: dissolving medium
Solute: substance that dissolves
When in solution, you cannot distinguish solvent and solute

4. What is a Solution?
Soluble – a substance that can dissolve in a given solvent
Miscible: two liquids that can dissolve in each other
Example: water and antifreeze
Insoluble – substance cannot dissolve
Immiscible: two liquids that cannot dissolve in each other
Example: oil & water

5. Why Do Some Substances Dissolve and not Others?
To dissolve, solute particles must dissociate from each other and mix with solvent particles
Attractive forces between solute and solvent must be greater than attractive forces within the solute
Process of surrounding solute particles with solvent particles is called SOLVATION
In water, it is also called HYDRATION

6. Aqueous Solutions of Ionic Compounds
Remember:
Water molecules are polar (+ and – ends)
Water molecules are in constant motion
When you put salt in water, water molecules collide with surface of crystal
Charged ends of water attract ions of salt
Dipole interaction (water/salt) is stronger than ions in crystal, so it pulls them away

7. Solvation

8. Aqueous Solutions of Molecular Compounds
Water is also a good solvent for many molecular compounds (Example: sugar)
Sugar has many O-H bonds (polar)
When water is added, the O-H bond becomes a site for hydrogen bonding with water
Water’s hydrogen bonds pulls the sugar molecules apart
Oil is not a good solute because it has many C-H bonds (not polar) and few or no O-H (polar) bonds

9. Factors that Affect Solvation Rate
Increase Solvation Rate (Dissolve Faster) by:
Agitation (stirring)
Increase surface area (make particles smaller)
Temperature (make it hotter)
All these increase the number of collision between water and the solute

10. Heat of Solution
During Solvation it takes energy to make the solute particles come apart.
Solvent particles must also move apart
This energy requirements is called “Heat of Solution”

11. Solubility Has Anyone ever made rock candy?
How much water does it take to dissolve the sugar at room temperature?
What happens when we raised the temperature?
Only a limited amount of solute can dissolve in a given amount of solvent
Every solute is unique for the solvent
This is ‘Solubility’ – the amount of solute that can dissolve in a given amount of solvent at a specified temperature and pressure

12. Solubility Continued
Solubility can also be understood at the particle level:
As particles collide, some particles are deposited back to the solute
Some particles are removed from the solute.
When the rate of deposit equals the rate of solvation, then the solution is SATURATED
Saturated Solution – no more solute can be dissolved in the solvent at this temperature and pressure
Unsaturated Solution – there is still room for more solute to be dissoved

13. Factors that Affect Solubility
Most substances are MORE soluble at high temperature than at low
If you dissolve a substance until saturated at high temperature and then reduce the temperature, the solution becomes “supersaturated”
Supersaturated solutions are unstable
A small change makes the solute reappear
Rock candy worked that way. How?

14. Factors that Affect Solubility
Pressure affects solubility of gaseous solutes
Carbonated beverages
Henry’s Law
At a given temperature solubility (S) of a gas in a liquid is directly proportional to pressure (P) S2 =
S1P1 P2 S1 P1 = S2 P2 OR

15. Solution Concentration
Section 15.2

16. Expressing Concentration
Concentration is a measure of how much solute is dissolved in a specific amount of solvent.
Concentration can be qualitative or quantitative
Qualitative: strong, weak, etc.
Quantitative: percent by mass, percent by volume, molarity, molality

17. Using Percent to Express Concentration
Percent by mass =
Mass of solute
Mass of solution
X 100
Percent by volume =
Volume of solute
Volume of solution
X 100

18. Molarity
Molarity is the most common method of expressing concentration in Chemistry
Molarity is moles of solute in 1 liter of solution.
You make it by taking 1 mole of a solute and filling up with solvent to the 1 liter level.
Molarity (M) =
Moles of solute
Liters of solution

19. Molarity - Example SOLVE for Mole/Liter: 5.10g glucose X 1 mol glucose
An IV solution contains 5.10 g of glucose (C6H12O6) in 100.5ml of water. What is the molarity of this solution?
Known:
Mass of solute = 5.10 g glucose
Molar mass of glucose = g/mol
Volume of solvent = ml
SOLVE for Mole/Liter:
5.10g glucose X
1 mol glucose
180 g/mol glucose
= mol glucose
Convert ml to liters:
100.5 ml X
1 L
1000 ml
= L
0.028 mol L
Moles
Liter
= 0.28 M
Molarity = =

20. Preparing Molar Solutions
How do you prepare a 1.5M solution of sucrose (C12H22O11) ?
1.5 moles sucrose x 342g/mol = 513 g sucrose
1.5 Molar would be 513g in 1 L of water
Measure out 513 g sucrose
Put it in a 1L graduated cylinder
Add distilled water to make 1L total solution
To make 100ml, use 1/10th of each
51.3g sucrose in 100ml of water

21. Making Dilute Solutions
Concentrated HydroChloric Acid is 12M.
How would I make ½ the concentration, or 6 M ?
Use M1V1 = M2V2
12moles x 1L = 6moles x ?L
= 12moles x 1L/6 moles = 2 L
So put in twice the solvent and you have ½ the concentration.

22. Molality and Mole Fraction
Molality is Moles of Solute per 1 kg of Solvent
Abbreviated m and is read as molal.
This is because volume increases with temperature and this changes the molarity.

23. Calculating Molality
If a student adds 4.5 g of sodium chloride to 100.0g of water, what is the molality?
Known:
Mass of water is g
Mass of sodium Chloride is 4.5g
Unknown: m or mol/kg
4.5g NaCl X
1 mol NaCl
58.5 g NaCl
= mol NaCl
100.0 g water X
1 kg H2O
1000 g H20
= kg H2O
m =
Moles of solute
Kg solvent =
0.077 mol NaCl
kg H2O
= 0.77 mol/kg

24. Mole Fraction
Mole fraction = moles solute divided by total moles of solute + solvent
Mole Fraction (X) =
___nA__
nA + nB
Example: What is the mole fraction of hydrochloric acid if for every 100 g of solution, 37.5 g is HCl
37.5 g HCl x
1 Mol HCl
36.5 g HCl
= 1.03 mol HCl
62.5 g H2O x
1 mole H2O
18.0 g H2O
= 3.47 mol H2O
XHCl =
___nHCL___
nHCl + nH2O =
_____1.03 mol HCl_______
1.03 mol HCl mol H2O
= 0.229

25. Colligative Properties of Solutions
Chapter 15.3

26. Electrolytes and Colligative Properties
When solutions are made, the physical properties of the solutions are affected by the number of particle dissolved
Colligative: depending on the collection

27. Colligative Properties
Electrolytes vs non-electrolytes
Ionic compounds ARE electrolytes because they form ions in solution that conduct electricity
Molecular compounds ARE NOT electrolytes because they do not conduct electricity
Vapor Pressure Lowering
Adding a non-volatile solute lowers the vapor pressure of the solution (vs. solvent)
More solute  more vapor pressure lowering

28. Colligative Properties
Boiling Point Elevation
Because vapor pressure is lowered, it takes more energy to make it boil
Boiling point temperature is raised
Boiling point elevation is directly proportional to solution molality
What is the benefit of adding salt to boiling water for pasta?
Freezing Point Depression
Freezing point temperature is lowered
Solute particles interfere with attractive forces of solvent
Freezing point of a solution is always lower than the freezing point of a pure solvent
FP Depression is directly proportional to molality

29. Colligative Properties
Osmosis and Osmotic Pressure
Diffusion: mixing of gasses or liquids through random motions
Osmosis is diffusion of solvent through a semi permeable membrane from high solvent concentration to lower solvent concentration
Living cells use this to get materials in/out of cells

30. Colligative Properties
Example: Salt/water
During Osmosis, Water molecules move both directions through membrane
But only water can move through the membrane
So pure water builds up on one side of the membrane
Water/salt builds up on the other.
Higher concentration of water on one side creates:
Osmotic pressure
A pressure or push to equalize the water/salt concentrations
Pressure depends on concentration of solute

31. Colligative Properties - Antifreeze

32. Freezing Point Depression
B. Types
Freezing Point Depression
View Flash animation.

33. Boiling Point Elevation
B. Types
Boiling Point Elevation
Solute particles reduce vapor pressure of solvent, requiring more energy for vapor pressure to reach atmospheric pressure (boiling), thus raising the boiling point temperature.

34. B. Types Applications salting icy roads making ice cream antifreeze
cars (-64°C to 136°C)
fish & insects

35. C. Calculations t: change in temperature (°C)
t = k · m · n
t: change in temperature (°C)
k: constant based on the solvent (°C·kg/mol)
m: molality (m)
n: # of particles

36. C. Calculations # of Particles Nonelectrolytes (covalent)
remain intact when dissolved
1 particle
Electrolytes (ionic)
dissociate into ions when dissolved
2 or more particles

37. C. Calculations GIVEN: WORK: b.p. = ? m = 0.73mol ÷ 0.225kg tb = ?
At what temperature will a solution that is composed of 0.73 moles of glucose in 225 g of phenol boil?
GIVEN:
b.p. = ?
tb = ?
kb = 3.60°C·kg/mol
WORK:
m = 0.73mol ÷ 0.225kg
tb = (3.60°C·kg/mol)(3.2m)(1)
tb = 12°C
b.p. = 181.8°C + 12°C
b.p. = 194°C
m = 3.2m
n = 1
tb = kb · m · n

38. C. Calculations GIVEN: WORK: f.p. = ? m = 0.48mol ÷ 0.100kg tf = ?
Find the freezing point of a saturated solution of NaCl containing 28 g NaCl in 100. mL water.
GIVEN:
f.p. = ?
tf = ?
kf = 1.86°C·kg/mol
WORK:
m = 0.48mol ÷ 0.100kg
tf = (1.86°C·kg/mol)(4.8m)(2)
tf = 18°C
f.p. = 0.00°C - 18°C
f.p. = -18°C
m = 4.8m
n = 2
tf = kf · m · n

39. Heterogeneous Mixtures
Chapter 15.4

40. Types of Heterogeneous Mixtures
Look like a solution, but are really mixtures
Mixtures of substances that exist in 2 different phases
2 Types:
Suspensions
Colloids
Solutions:
Particles of solute are atomic sized compared to solvent

41. Suspensions Particle Size
Suspended particles are large compared to solvent
Larger than 1000 nm for solvated particles
CAN be filtered
When stirred, solid-like state begins to flow like a liquid
Called Thixotropic
Examples
housepaint

42. Colloids Particle Size Cannot be Separated by filtration or settling
Particles of solute are intermediate sized (between atomic and large suspension sized) compared to solvent
Between 1 nm and 1000 nm diameter
Cannot be Separated by filtration or settling
Example: milk, butter, cheese,

43. Colloids Types of Colloids Solid Sol: Solid in solid (gemstones)
Sol: Solid in Liquid (Blood, gelatin)
Solid emulsion: Liquid in solid (butter, cheese)
Emulsion: liquid/liquid (milk, mayonaise)
Solid foam: gas/solid (marshmallows, soap that floats)
Foam: gas/liquid (whipped cream, beaten egg whites)
Aerosol: solid/gas (smoke, dust in air)
Aerosol: liquid/gas (clouds, spray deodorant

44. Brownian Motion
Liquid colloid under a microscope shows random, jerky motions of dispersed particles
Brownian motion
From collisions of particles of dispersion medium with dispersed particles
Collisions prevent particles from settling out
Due to polar or charged atomic particles
Link for display

45. Tyndall Effect
Dilute Colloids sometimes appear as clear solutions (concentrated colloids do not)
Because particles are too small to be seen with naked eye
But: dispersed colloid particles are large enough to scatter light
Tyndall effect
Solutions do not scatter light (particles are too small)

46. Tyndall Effect
Colloid
Solution

47. Chapter Summary Chapter 15 Test on Friday (5/16)
Chapter 15 Vocabulary Due Friday (5/16)
Chapter 15 HO’s (remaining) Due Friday (5/16)

48. Chapter Test Covers: Characteristics of Solutions
Solvation – ionic vs molecular
Factors Affecting Solubility
Solution Concentrations: Calculate
Percent by mass
Percent by volume
Molarity
Molality
Colligative Properties of Solutions
Suspensions and Colloids