1. Solutions

2. Solutions: Basic Definitions
Solute – substance that is being dissolved
Solvent – substance that dissolves the solute
Solution – a mixture of substances that has a uniform composition; a homogeneous mixture

3. Solutions: Basic Definitions
Soluble – when a substance will dissolve in another substance (salt & water)
Insoluble – when a substance will not dissolve in another substance (sand & water)

4. Solutions: Basic Definitions
Miscible – when two liquids are soluble in each other (alcohol & water)
Immiscible – when two liquids are not soluble in each other (oil & water)
Aqueous – dissolved in water

5. Solutions: Basic Definitions
unsaturated solution - If the amount of solute dissolved is less than the maximum that could be dissolved
saturated solution - solution which holds the maximum amount of solute per amount of the solution under the given conditions
supersaturated solution - solutions that contain more solute than the usual maximum amount and are unstable.

6. Supersaturated Solutions
They cannot permanently hold the excess solute in solution and may release it suddenly.
Supersaturated solutions, as you might imagine, have to be prepared carefully.
Generally, this is done by dissolving a solute in the solution at an elevated temperature, at which solubility is higher than at room temperature, and then slowly cooling the solution.

7. Solutions: Basic Definitions
Suspension – mixture containing particles that will settle out is left undisturbed (cornstarch & water)
Colloid – heterogeneous mixture that will not settle out if left alone (blood)
Emulsion – colloid in which a liquid is suspended in another liquid (mayo)

8. Dissolution of a Solid in a Liquid
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9. Solutions: Basic Definitions
Electrolyte – solution that conducts an electric current
Non electrolyte – solution that does not conduct an electric current

10. Reading Solubility Graphs
According to the graph above, about how many grams of KBr are needed to make a saturated solution in 100 g of water at 30° C?
70 grams KBr

11. Reading Solubility Graphs
According to the graph above, what kind of solution would you have if you dissolved 10 g of KCl in 100 g of water at 0°C?
Unsaturated

12. Solubility
Solvation – process of surrounding solute particles with solvent particles to form a solution
The rule for dissolving solutions is “like dissolves like”
Polar substances will dissolve in polar solvents
Non polar substances will dissolve in non polar solvents
Non polar will NOT dissolve in polar and vice versa

13. Solubility Rules!!!

14. Increasing the Rate of Solution
Agitation
Increasing Temperature
Increasing Surface Area

15. Agitation Increases the speed of the particles
speeds up the dissolving process in solids.

16. Increasing Temperature
More collisions of particles as temperature increases.

17. Particle Size (Increasing Surface Area)
Smaller particles dissolve faster than larger particles.
more surface area
Sugar cube vs. ½ teaspoon sugar
Teaspoon will dissolve faster

18. Solubility of a gas
Two main factors that affect the solubility of a gas in a liquid
Temperature
Normally, the higher the temperature, the faster a solute will dissolve…NOT with a gas!
In a gas, the cooler the temperature, the faster the gas will dissolve
Think of drinking a coke…what’s fizzier, a cold coke or a hot coke?

19. Solubility of a gas
The second factor affecting the solubility of a gas is pressure
Pressure
The higher the pressure, the more gas that will dissolve
Think of a coke bottle…What will happen if you leave the lid off?

20. Concentration Concentration units can vary greatly.
They express a ratio that compares an amount of the solute with an amount of the solution or the solvent.
For chemistry applications, the concentration term molarity is generally the most useful. Abrv. (M)

21. % by Mass Remember … % = part x 100 whole
% by mass = mass solute x 100
mass solution

22. Example
What is the % by mass of a solution with 3.6 g of NaCl dissolved in g of water?
Remember what will the Total solution be!!
% = (3.6 / 103.6) x 100 = 3.5% NaCl

23. % by Volume Remember … % = part x 100 whole
% by volume = volume solute x 100
volume solution

24. Example
What is the % by volume of 75.0 ml of ethanol dissolved in ml of water?
Remember what will the Total solution be!!
% = (75.0 ml / ml) x 100 = 27.3%

25. Molarity
Molarity is defined as the number of moles of solute per liter of solution.
Molarity = moles of solute/liter of solution
Note that the volume is the total solution volume that results, not the volume of solvent alone.

26. Molarity Examples
Calculate the molarity of a solution made by dissolving 23.4 g of sodium sulfate in 125 ml of solution
23.4 g Na2SO4  mol
125 ml  L
M = mol / L
M = 0.165mol / L
M = 1.32 M

27. Molarity Examples
Calculate the molarity of a solution made by dissolving 5.00 g of C6H12O6 in enough water to make ml of solution
5g/180g = 0.028mol
0.028mol/0.100L
0.280 M

28. Molarity Examples
How many grams of Na2SO4 are required to make L of a M solution of Na2SO4?
24.9 g Na2SO4

29. Dilution
When chemists purchase solutions, they generally purchase “stock solutions” which are extremely concentrated solutions
This way a chemist can dilute the strong solution to any concentration that they wish. This stops the chemist from having to buy several concentrations

30. Dilution Equation M1V1 = M2V2 M1 = initial molarity
V1 = initial volume
M2 = final molarity
V2 = final volume
The units for V1 & V2 do not matter as long as they are the same
M1 & M2 MUST be in molarity

31. Dilution Problems
Suppose we want to make 250 ml of a 0.10 M solution of CuSO4 and we have a stock solution of 1.0 M CuSO4. How would we prepare the solution?
First do the math
M1V1 = M2V2
(1M)V1 = (.1M)(250ml)
V1 = 25 ml
Take 25 ml of 1M CuSO4 and add it to 225 ml H2O

32. More Dilution Problems
How many ml of 3.0 M H2SO4 are required to make 450 ml of a 1.0 M solution?
150 mL

33. molality Molality = moles of solute kg of solvent
Must have the appropriate units
Abrv (m)

34. Colligative Properties

35. Colligative Properties
Colligative properties – physical properties of solutions that are affected only by the number of particles NOT the identity of the solute
They include:
Vapor Pressure Lowering
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure
In all of these we will be comparing a pure substance to a mixture

36. Vapor Pressure Lowering
Vapor Pressure – the pressure exerted in a closed container by liquid particles that have escaped to the surface and entered the gas phase

37. Vapor Pressure Lowering
The vapor pressure of a mixture is lower than a non volatile pure substance due to the fewer number of particles that are able to escape into the gas phase

38. Vapor Pressure Lowering: Liquid/Vapor Equilibrium
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39. Vapor Pressure Lowering: Addition of a Solute
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40. Boiling Point Elevation
The boiling point of a solution is the point at which enough energy has been added to overcome the intermolecular forces that hold the solute in the solution.
At this point, the molecules gain enough kinetic energy to produce a pressure that is greater than the atmospheric pressure keeping them in solution
Once this point is reached, the solution vaporizes (becomes a gas)
The boiling point of a mixture is higher that the boiling point of a pure substance

41. Boiling Point Elevation: Liquid/Vapor Equilibrium
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42. Boiling Point Elevation: Addition of a Solute
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43. Boiling Point Elevation: Solution/Vapor Equilibrium
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44. Freezing Point Depression
The freezing point of a solution is the point where enough energy has been removed from the solution to slow the molecules down and increase intermolecular forces so the solution becomes a solid
The freezing point of a mixture is lower that the freezing point of a pure substance

45. Freezing Point Depression: Solid/Liquid Equilibrium
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46. Freezing Point Depression: Addition of a Solute
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47. Freezing Point Depression: Solid/Solution Equilibrium
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48. What is Osmosis?
Suppose a salt solution and water are separated by a semipereable membrane
Water will move through the membrane from into the salt solution to equalize the concentrations on each side of the membrane.
This is osmosis

49. Osmotic Pressure
Osmotic pressure is the pressure exerted on the semi permeable membrane by the movement of the water

50. Osmosis Click in this box to enter notes.
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51. Micelle Formation: The Cleansing Action of Soap
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