1. Concentrations & Solutions
Unit 12

2. Mixtures Combination of 2 or more different substances
Heterogeneous mixtures – can see the parts (trail mix)
Homogeneous mixtures – mixture appears uniform (Kool-aid)

3. Types of Mixtures
1. Suspensions 2. Solutions 3. Colloids

4. Suspension Heterogeneous mixture
Particles remain mixed with liquid when stirred but separate spontaneously over time
Example – flour & water

5. Suspension
Flour & water

6. Solution Homogeneous mixture with even distribution of particles
Can be gas (air) or solid (brass)
Most often liquid
Solutes dissolved in solvent
Aqueous solution – water is solvent

7. Solution

8. Colloid Stable heterogeneous mixture
Appears homogeneous to naked eye b/c even distribution
BUT components visible under microscope
Does not settle when left to stand

9. Colloid

10. Separating Mixtures
Decanting – pour off liquid

11. Separating Mixtures
Centrifuge – spin to separate by density

12. Separating Mixtures
Filtration – liquid through filter

13. Separating Mixtures
Evaporation – leaves behind solid

14. Separating Mixtures
Chromatography - based on dissolving rates

15. Separating Mixtures
Distillation – separate by boiling point

16. Concentration Ratio of solute to solvent
Consistent throughout solution
Calculating concentration
Parts per million (ppm)
Molality (m)
Molarity (M)
g solute
g solvent
moles solute
kg solvent
moles solute
L solution

17. Molarity (M) M is read as “molar” or “moles per liter”
Any amount with the same molarity will have the same concentration or ratio of solutes to solvent
So 1 mL of 1 M HCl has the same concentration as 20 L of 1 M HCl

18. Preparing a Solution
When preparing a solution, you must have the correct total volume
1.00 mole solute L solvent DOES NOT equal 1.00 M solution!
Instead you need 1.00 L total solution
So dissolve solute in small amount of solvent and then add more solvent to get the correct total volume of solution

19. Calculating Molarity 0.75 M KBr M = 0.30 moles KBr = 0.40 L solution
0.30 moles of KBr are dissolved in 0.40 L of solution. What is the molarity?
M = 0.30 moles KBr =
0.40 L solution
0.75 M KBr

20. Calculating Molarity
What is the molarity of a KCl solution that has a volume of mL and contains 85.0 g of KCl?
Two problems
Grams mL

21. Molarity Calculations
How many grams of CaCl2 are needed to make 625 mL of a 2.0 M solution?

22. Dilution Adding solvent to solutions to decrease the concentration
Does not change the number of moles of the solute that are present
M1V1 = M2V2

23. Practice
2.0 L of a 0.88 M solution are diluted to 3.8 L. What is the new molarity?

24. Practice
You have 150 mL of 6.0 M HCl. What volume of 1.3 M HCl can you make?

25. Solubility The ability of a solute to dissolve in a solvent
Measured in terms of the amount of a solute that will dissolve in a given amount of solvent

26. Solubility – “Like dissolves like”
Polar substances tend to dissolve in other polar substances
Nonpolar substances tend to dissolve in other nonpolar substances
Degree of polarity also matters
Miscible – liquids that are completely soluble in each other

27. Solubility – “Like dissolves like”
Polar + nonpolar doesn’t usually dissolve
Immiscible – 2 or more liquids that do not mix with each other

28. How can we speed the dissolving process?
Shaking or stirring
Increases the surface area contact between the solute & solvent
Increasing the temperature
More energy available for dissolving

29. Effects of temp on solubility
ID trends
Least soluble
Most soluble
Extrapolate data
200 g at 50 oC
Precipitate formed from cooling

30. Saturation There is a maximum amount of solute that can be dissolved
Saturated solution
Less than that maximum amount
Unsaturated solution
More than that maximum amount
Supersaturated solution

31. Colligative Properties
Any physical effect of the solute on the solvent
Not specific to the solute present but rather caused by the presence of a solute
Examples
Boiling point elevation
Freezing point depression