1. Solutions
Chapter 18

2. Recall….. Solutions are homogeneous mixtures
that may be solid, liquid, or gas

3. Examples Scuba Tank Salt-Water Aquarium
Solution of oxygen and several other gases.
Salt-Water Aquarium
In this solution aquarium salt is the
solute, water is the solvent.

4. Solutions and Other Mixtures
6.1
Solutions and Other Mixtures
Suspension – a mixture that looks uniform when stirred or shaken that separates into different layers when it is no longer agitated
Colloid – a mixture of very tiny particles of pure substances that are dispersed in another substance but do not settle out of the substance
Emulsion – any mixture of immiscible liquids in which the liquids are spread throughout one another

5. Suspensions The pulp in orange juice is spread throughout the
mixture right after the juice is shaken – over time, the
pulp does not stay mixed with the water molecules
and settles to the bottom of the container.

6. Examples of suspensions
Water and coffee
Oil and vinegar
Sand and water
Water and oil
Blood

7. Examples of colloids Egg whites Paint
Whipped cream (dispersing gas in a gas)
Marshmallows (dispersing gas in a solid)
Fog (water dispersed in air)
Smoke (solid particles dispersed in air)

8. Emulsions Examples: Ice cream Milk Mayonnaise
Emulsifying agents like soap and detergent allow the formation of colloidal dispersions between liquids that do not ordinarily mix

9. Factors determining solubility
Temperature
Stirring (agitation)
Surface area

10. Properties of Solubility
Miscible – two liquids are miscible IF they dissolve in each other
EXAMPLE: Water and alcohol
Immiscible – liquids that are insoluble in each other
EXAMPLE: Oil and vinegar

11. Factors affecting solubility
Solubility of most solid substances increases as temperature of solvent increases
Solubility of gases is greater in cold water than hot water

12. The Dissolving Process
More solid will dissolve as temperature increases
Less gas will dissolve as
temperature increases

13. Henry’s Law
…at a given temperature the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid
(simply put, as pressure of gas above the liquid increases, the solubility increases; similarly, as pressure of the gas decreases, the solubility of the gas decreases)

14. Solubility Curve Graphs

15. What mass of sodium nitrate
will dissolve in 100cm3 of water at 50°C?
About 112g

16. How much oxygen will dissolve in 100g
water at 80C°?
0.5 mg
How much oxygen will dissolve in
100g water at 10C°?
1.3 mg

17. Henry’s Law - Equation S1 S2 P1 P2 ------ = ------=
P1 P2
Solubility # 1 divided by pressure # 1 is equal to
Solubility # 2 divided by Pressure #2

18. Henry’s Law - Example
If the solubility of a gas in water is 0.77 g/L at 3.5 atm of pressure what is its solubility (in g/L) at 1.0 atm of pressure? (The temperature is held constant at 250C)
1. ANALYZE List the knowns and the unknown.
Knowns: Unknown:
P1 = 3.5 atm S2 = ? g/L
S1 = 0.77 g/L
P2 = 1.0 atm
Henry’s Law: S1/P1 = S2/P2

19. Example - continued 2. Calculate Solve for the unknown.
Solving Henry’s law for S2 yields
S2 = S1 X P2 P1
Substituting the known values and calculating yields
S2 = 0.77 g/L X 1.0 atm = 0.22 g/L
3.5 atm

20. Example continued 3. Evaluate Does the result make sense?
The pressure is reduced (from 3.5 atm to 1.0 atm, so the solubility of the gas should decrease, which it is shown to do. Because the new pressure is approximately one-third of the original pressure, the new solubility should be approximately one-third of the original, which it is. The answer is correctly expressed to two significant figures.

21. Concentrations of Solutions
Concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent
A dilute solution is one that contains only a low concentration of solute
A concentrated solution contains a high concentration of solute

22. Molarity (M) THE most important unit of concentration in chemistry……
Molarity (M) is the number of moles of a solute dissolved per liter of solution

23. Molarity Molarity = moles of solute or M = mol liters of solution L
For example: to calculate the molarity when 2 mol of glucose is dissolved in 5 L of solution, divide the number
of moles by the volume in liters.
2 mol glucose
5 L of solution =
0.4 mol/L = 0.4 M
mole

24. Molarity Calculations
Rearrange the equation:
Moles of solute = molarity (M) X liters of solution (V)
Moles of solute = M1 X V1
M1 X V1 = M2 X V2
V1 = M2 X V2 / M1

25. Colligative Properties
Colligative Properties – properties that depend only on the number of particles dissolved in a given mass of solvent. Three important ones:
Vapor-pressure lowering
Boiling-point elevation
Freezing-point depression

26. Colligative properties
Vapor pressure – the pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system
Boiling-point Elevation – the difference in temperature between the boiling point of a solution and that of the pure solvent
Freezing-point depression – the difference in temperature between the freezing point of a solution and that of the pure solvent

27. Calculations involving Colligative Properties
Molality (m) – is the number of moles of solute dissolved per kilogram (1000g) of solvent. (Also known as molal concentration)
Molality = moles of solute
kilogram of solvent
moles of solute = moles of solute
kilogram of solvent g of solvent

28. Percent composition Percent by volume (% v/v) =
Volume of solute
Volume of solution X 100
Percent (mass/volume) (% m/v) =
mass of solute (g)
volume of solution (mL) X 100

29. Assignment Complete calculations…. Practice Problems # 1,2 pg 507

30. Problems page 507
1. The solubility of a gas in water is 0.16g/L at 104 kPa of pressure. What is the solubility when the pressure of the gas is increased to 288 kPa? (Assume the temperature is constant)
2. A gas has a solubility in water at 0 C of 3.6 g/L at a pressure of 1.0 atm. What pressure is needed to produce an aqueous solution containing 9.5 g/L of the same gas at 0 C?

31. Problems page 511
8. A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution?
9. A solution has a volume of 250and contains 0.70 mol NaCl. What is its molarity?

32. Problems page 511
10. How many moles of ammonium nitrate are in 335 mL of 0.425M NH4NO3?
11. How many moles of solute are in 250 mL of 2.0 M CaCl2? How many grams of CaCl2 is this?

33. Problems page 513
12. How many milliliters of a stock solution of 4.00M KI would you need to prepare mL of 0.760M KI?
13. Suppose you need 250 mL of 0.20M NaCl, but the only supply of sodium chloride you have is a solution of 1.0M NaCl. How do you prepare the required solution? Assume that you have the appropriate volume-measuring devices on hand.

34. Problems page 514
14. If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone of this solution?
15. A bottle of hydrogen peroxide antiseptic is labeled 3.0% (v/v). How many mL H2O2 are in a mL bottle of this solution?

35. Problems page 515
16. Calculate the grams of solute required to make 250 mL of 0.10% MgSO4 (m/v).
17. A solution contains 2.7g CuSO4 in 75 mL of solution. What is the percent (mass/volume) of the solution?

36. Problems page 521
28. How many grams of sodium fluoride are needed to prepare a 0.400m NaCl solution that contains 750.0g of water?
29. Calculate the molality of a solution prepared by dissolving 10.0g NaCl in 600g of water.