1. If you are not part of the precipitate, you are part of the solution…
Chapter 15
Solutions
If you are not part of the precipitate, you are part of the solution…

2. solutions are everywhere!
air, shampoo, soda, gasoline, cough syrup, etc…
defined simply as a homogeneous mixture
Solvent: substance in largest amount
Solute: other substances
in “aqueous solutions” (aq), water is the solvent

3. 15.1 solubility
when an ionic compound dissolves, it conducts electricity
ionic compounds separate into their ions

4. as it dissolves, water molecules surround and rip away the ions

5. notice which end of the water butts up against the cations & anions

6. 15.1
Dissolving a solid

7. 15.1
water can also dissolve polar substances like ethanol

8. 15.1
the H-bonding plays a big role here

9. sucrose dissolves well, why?
H-bond attraction! (see all the OH’s)

11. not everything can dissolve in water
if it doesn’t have the structure for H-bonding and it’s not polar, then water
molecules don’t have a
way to attach to it and
dissolve it

12. 15.1

13. 15.1 like dissolves like Polar substances dissolve polar stuff
Nonpolar substances dissolve nonpolar stuff
The characteristics of the solvent must match the characteristics of the solute
Polar
H-bonding
Nonpolar

14. 15.2 solution concentration
there is a limit to how much you can dissolve; like sugar in iced tea
when the limit is reached, the solution is saturated
The Temperature of the solvent plays a role (think of iced tea vs hot tea)
if a solvent still hold more solute, it is unsaturated!

15. 15.2
sometimes when a saturated solution is allowed to cool, it will remain saturated without crystals coming out
It is supersaturated: a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances
Supersaturated solutions are very unstable; a single crystal can cause the excess to crystallize out

16. 15.2
Supersaturated Solution

17. concentrated and dilute
concentrated a lot of solute dissolved in the solvent
dilute a relatively small amount of solute dissolved.
Super saturated the solvent holds more solute than it should
Are those qualitative or quantitative terms?
Qualitative

18. 15.3 factors affecting the rate of dissolution
There are three key factors on how fast a solute dissolves
surface area
stirring
temperature

19. 15.3
Dissolving occurs at the surface of a solid, so the more surface area exposed to a solvent, the faster it will dissolve (powdered sugar v. sugar cube)
Stirring moves the particles of solute away from the solid mass and helps bring in fresh particles of solvent
Increasing the temperature speeds up the particle motion. Also, most solvents can dissolve more solutes at higher temps

20. Solubility Curve
How much silver nitrate will there be in a saturated solution at 10o C?
How would you describe a solution of KBr that had 100 g at 60o C?

21. the opposite is true for gases dissolved in water
15.3
the opposite is true for gases dissolved in water
higher T or more stirring means they don’t dissolve well
Consider the effects of heating and stirring on a soda…

22. 15.3 solutions of gas also depend on pressure
lower the pressure and the gases are more easily released

23. 15.3 higher pressure can “force” more gas into a liquid
cans and glass bottles can keep gases under pressure

26. 1986: Hundreds gassed in Cameroon lake disaster
At least 1,200 people are feared dead and hundreds more hospitalized after a cloud of lethal gas escaped from a volcanic lake in West Africa
Most of the victims died in their sleep.
The gas killed all living things within a 15-mile radius of the lake, the area is still highly contaminated.
It is not yet known what caused the gas to escape the lake
Eyewitnesses described how the normally clear waters of the lake turned a reddish brown, while a sudden wind arose and whipped up huge waves.

27. 15.3
Lake Nyos, Cameroon
1,700 people killed in 1986

28. 15.3
Lake Nyos, Cameroon
1,700 people killed in 1986

29. Questions?

31. Quantitative Concentration
Students know how to calculate the concentration of a solute in terms of
grams per liter
molarity
parts per million
percent composition.

32. Parts per million
The Salton Sea contains 44 grams of salt per 1000 grams of water.
What is the concentration in parts per million (ppm)?
first, calculate how many parts there are per gram, then convert that to parts per million
44g/1000g =
.044 x 1,000,000 =
.044
44,000 ppm

33. Questions? 33

34. Molarity
molarity: a measure of the concentration of a solute in a solution.
molarity = moles solute/Liter solution
M = mol / L
e.g. a 2.7M soln means there are 2.7 mol of solute per liter of solution
given that M = mol/L, you should be able to solve for any one variable if you know the other two

35. example 2.25 M = How many mols HCl are in 3.0 L of a 2.25 M soln? mol
M = mol/L
How many mols HCl are in 3.0 L of a 2.25 M soln?
mol
3.0 L
2.25 M =
2.25 M • 3.0 L = mol
6.8 = mol

36. example 2.00 M = How many grams are in 2.50 L of a 2.00 M NaCl soln?
5.00 mol g
1 mol
mol
2.50 L =
2.00 M =
293 g NaCl
2.00 M • 2.50 L = mol
5.00 = mol

38. the properties of solns: boiling point and freezing point
Colligative properties are properties of solutions that depend upon the ratio of the number of solute particles to the number of solvent molecules in a solution, Colligative properties include:
lowering of vapor pressure
Elevation of boiling point
Depression of freezing point
Osmotic pressure.

39. the solute interferes with the formation of bubbles and raises the boiling point

40. Therefore it takes more energy to form the bubbles
add more solute and the bp goes higher
it doesn’t matter what the solute is, just how much

41. Salutes also interfere with freezing
They get in the way of building a solid, lowering the freezing point

42. both the raising of bp and the lowering of fp is seen when we add antifreeze to water

43. Questions?