1. Chapter 15
Solutions

2. solutions are everywhere!
air, brass, shampoo, Diet Coke, gasoline, cough syrup, etc.
defined simply as a homogeneous mixture (chm a)
substance in largest amt = solvent
other substances = solute
in aqueous solns water is solvent

3. 15.1 solubility when an ionic cmpd dissolves, it conducts electricity
therefore ionic cmpds break up into their ions

4. 15.1
as it dissolves, waters surround and rip away the helpless ions

5. 15.1
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 here; why?

8. 15.1 the H-bonding plays a big role here
the more you look like water the more likely it will dissolve you

9. 15.1 why do you think sucrose here dissolves so well?
H-bond attraction! (see all the OH’s?)

11. not everything can dissolve in water
if you have no polar handle on you, water doesn’t recognize you
like the long nonpolar hydrocarbon above

12. 15.1

13. 15.1
so to dissolve in water you have to be able to break the net, to interrupt the H-bonding; you have to fit in
polar molecules and ionic cmpds can do that; nonpolar cannot
like dissolves like is a good general phrase
nonpolar solutes can dissolve into nonpolar solvents, too!

14. 15.1
sugar
sugar in np solvent
sugar in water

15. 15.1
grease
grease in np solvent
grease in water

16. 15.2 solution concentration
there is a limit to how much you can dissolve; like sugar in iced tea
when the limit is reached = saturated
depends on T (think: iced T vs hot tea)
can it still hold more solute?
unsaturated!
add more it will dissolve…

17. 15.2
sometimes when a saturated soln is allowed to cool, it will remain saturated without crystals coming out!!!
= supersaturated
very unstable; a single crystal will cause the xs to crystallize out to saturation

18. 15.2
Supersaturated Solution

19. 15.2
chemists also use concentrated and dilute - both really qualitative terms
concentrated basically means there’s a lot of stuff dissolved in there
dilute means not so much
but neither tells us about how much (quantitative)

20. 15.3 factors affecting the rate of dissolution
Three big factors here on how fast something dissolves
surface area
stirring
temperature

21. 15.3 dissolving occurs at the surface of a solid, so…
the more surface exposed to a solvent, the faster it will dissolve
like powdered sugar vs rock candy
fine salt vs rock salt

22. 15.3 stirring will increase the rate, too
in slow motion the solute is dissolved in the solvent, but
instead of hanging around and getting in the way, stirring gets them out of the way
this exposes new solute to new solvent

23. 15.3 raising the T means speeding up the solvent molecules
this lets them get their job done faster
not only does it happen faster, but most solutes dissolve more completely at higher T’s…

24. 15.3

25. 15.3 but! the opposite is true for gases dissolved in water
higher T or more stirring means they don’t dissolve well
that’s why we don’t heat up soda or aquariums, and why we don’t stir (shake) soda

26. 15.3 why do carbonated beverages do this?
sol of gas also depends on pressure
release the P and bye bye gases

27. 15.3 can “force” more gas into liq w/ higher pres
cans and glass bottles can keep gases under pres; not plastic

28. 15.3
Lake Nyos, Cameroon overturned
2000 people killed in 1986

29. 15.5 molarity concentration with numbers!
most commonly used unit is molarity
molarity (M) = moles solute/L soln
e.g. a 2.7M soln means there are mol of crud per litre of soln
given that M = mol/l, you shd be able to solve for any one variable if I give you other two…

30. example 2.25 M = How many mols HCl are in 1.45 L of a 2.25 M soln? mol
M = mol/L
How many mols HCl are in 1.45 L of a 2.25 M soln?
mol
1.45 L
2.25 M =
2.25 M • 1.45 L = mol
3.26 = mol

31. example 6.5 M = How many mols HCl are in 3.5 L of a 6.5 M soln? mol
M = mol/L
How many mols HCl are in 3.5 L of a 6.5 M soln?
mol
3.5 L
6.5 M =
6.5 M • 3.5 L = mol
23 = mol

32. example 1.5 M = How many mols NaCl are in 2.5 L of a 1.5 M soln? mol
M = mol/L
How many mols NaCl are in 2.5 L of a 1.5 M soln?
mol
2.5 L
1.5 M =
1.5 M • 2.5 L = mol
3.8 = mol

33. example 1.34 M = How many grams are in 2.50 L of a 1.34 M NaCl soln?
3.35 mol g
1 mol
mol
2.50 L =
1.34 M =
196 g NaCl
1.34 M • 2.50 L = mol
3.35 = mol

34. 15.10 the properties of solns: boiling point and freezing point
when you add solute to water it boils at a higher T than 100˚C!
and freezes at less than 0˚C!
why does solute have this effect; raising bp and lowering fp
[BTW, it happens with all the solutes in all liquid solvents]

35. 15.10
those darn solute guys make it tough for the water to get into the bubble and exert vp!

36. 15.10

37. 15.10

38. 15.10
so we have to give them more E to maintain the vp to fight the atm above
add more the bp goes higher
notice it doesn’t matter what the solute is, just how many
= colligative property

39. 15.10 also interferes with freezing
they get in the way of building a solid
this means lowering the fp
like salt on ice!

40. 15.10
both the raising of bp and the lowering of fp is seen when we add antifreeze to water