1. PowerPoint Presentation by R. Schultz
Chemistry 20
Chapter 5 - Solutions
PowerPoint Presentation by R. Schultz

2. 5.1 Classifying Solutions
Solutions are homogeneous mixtures
solvent: part of solution present in greatest quantity – e.g. water in an aqueous solution
solute: the substance dissolved in the solvent – e.g. salt in a saltwater solution
types of solutions: not just solid in liquid, but gas in gas, gas in liquid, liquid in liquid, ……. (chart page 167)
Do questions 1, 2 page 168

3. 5.1 Classifying Solutions
aqueous solutions will be our main focus
Dissolving processes:
a solute bonds break (endothermic)
b solvent intermolecular bonds break (endothermic)
c new solute/solvent bonds form (exothermic)
ionic
molecular
Ec > Ea + Eb (exothermic); Ec< Ea + Eb (endothermic)

4. 5.1 Classifying Solutions
discuss question 4, page 170
discuss cold packs:

5. 5.1 Classifying Solutions
Electrolytes: substances that conduct electricity when dissolved in water (ionics and strong acids)
Non-Electrolytes: don’t (moleculars)
Theory: dissolved ionic compounds dissociate; the compound breaks apart to release free cations and anions
Dissociation equations:
NaOH(s) Na+(aq) + OH¯(aq)
K2SO4(s) K+(aq) + SO42ˉ(aq)

6. 5.1 Classifying Solutions
The dissociation equation shows what happens when ionics dissolve in water
starts with the pure ionic compound in (s) state and produces (aq) ions
Ionics with low solubility remain in (s) state
Acids – molecular compounds that ionize to form H+(aq) and an anion in water. Ionization equation:
HCl(g) H+(aq) + Clˉ(aq)

7. 5.1 Classifying Solutions
Difference between ionization and dissociation (and equations)?:
Do worksheet BLM 5.1.3B
ionization: acids – ions not initially present; they form in the presence of water
starting compound in pure state or (aq)
dissociation: ionics – ions already present in crystal lattice; they just separate
starting compound in (s) state
Discuss questions 3, 4, 6, page 175

8. 5.2 Solubility solubility:  the ability to be dissolved
saturated solution
supersaturated solution:
 the ability to be dissolved
 often expressed in g (solute) per 100 mL solution
 solution of maximum concentration under a given set of conditions
 solution of > maximum concentration under a given set of conditions

9. 5.2 Solubility
Gas solubilities low in general, but very important in some cases e.g. O2 in H2O
In a saturated solution dissolving never really stops; dynamic equilibrium exists between dissolving and crystallizing processes
dissolving 
undissolved solute dissolved solute
crystallizing

10. 5.2 Solubility
dynamic equilibrium: 2 opposing processes, occurring at same rate so that no net change is observed
experimental evidence: in a mixture of a saturated solution with some undissolved solute, the size of the crystals will increase over time, even though the mass of crystals remains unchanged

11. 5.2 Solubility Example 11a, page 179 NaCl(s) Na+(aq) + Clˉ(aq)
Example 11c, page 179
(NH4)2CO3(s)  2 NH4+(aq) + CO32-(aq)
Try 11b, 11d, page 179
Note the difference in equations for saturated & unsaturated

12. As pressure of a gas  solubility of that gas 
Solubility Generalizations:
Solubility of
Effect of Temperature
Effect of Pressure
Solids in liquids
As temp  solubility 
No appreciable effect
Liquids in liquids
Gases in liquids
As temp  solubility 
As pressure of a gas  solubility of that gas 

13. 5.2 Solubility Question 7, page 183 – discuss
Do questions 2a, 3c, 4, 5, 6

14. 5.2 Solubility
Do Lab 5.B.1 – handout to help with report

15. 5.2 Solubility Solubility Chart 2009-10 Data Booklet H+, NH4+ H+, Na+
K+, NH4+
only
K+, NH4+
K+, NH4+

16. 5.3 Concentration of Solutions
Concentration of solution: quantity of solute per quantity of solution (it’s always solution, not solvent)
Can use terms “concentrated” or “dilute”, but most often using numbers
Expressions of Concentration:
% by mass:
commercial hydrogen peroxide is 3

17. 5.3 Concentration of Solutions
For very small concentrations: parts per million, ppm, and parts per billion, ppb
Used for toxic environmental pollutants

18. 5.3 Concentration of Solutions
Examples:
Practice Problem 2, page 186
Practice Problem 6a, page 188
Do worksheet BLM 5.3.2, #1 – 4, and 6

19. 5.3 Concentration of Solutions
moles – because we are doing the course in different order from the text we need to deal with moles now
recall from Science 10: a mole (mol) is a gigantic # of particles (6.02 x 1023)
atoms and molecules are so small that gigantic #’s are needed to make them have a measurable mass
Green Pea Analogy, Moles Song
you don’t need to know this # by memory

20. 5.4 Preparing and Diluting Solutions
October 23 each year from 6:02 am to 6:02 pm is International Mole Day since date and time is 6:
National Chemistry Week in USA is week in which Mole Day falls
Could you write a moles song, a moles poem, dress up as a mole – I challenge you /

21. 5.4 Preparing and Diluting Solutions
1 mol of moles placed head to tail would cover a distance of 11 million light years!
They would have a mass of approximately 90% of the Moon

22. 5.3 Concentration of Solutions
molar mass: mass of 1 mol of a substance
Examples:
Molar Mass of sodium 22.99
Molar Mass of nitrogen
Molar Mass of (NH4)2CO3
nitrogen is N x = 28.02
you will need to calculate molar masses often as part of other calculations in every further chapter
in this chapter you need to show this working
in further chapters no

23. 5.3 Concentration of Solutions
Calculating # of moles of a substance
example: calculate # moles in 3.50 g Na3PO4
formula method unit cancelling method
mass of sample (g)
number of moles (mol)
molar mass
need mol; have g and
to get mol, do g since
g = g x = mol

24. 5.3 Concentration of Solutions
calculating mass of a substance from # of moles
example: calculate mass of 1.75 mol of Ca(NO3)2
formula method unit cancelling method m
n M
need g; have mol and
to get g do mol x
Do worksheet BLM 3.0.2

25. 5.3 Concentration of Solutions
Back to concentrations – molar concentration
don’t memorize this formula – get it upside down and you’re sunk
molar concentration units (mol/L) – that tells you everything you need
molar concentration (mol/L)
# moles solute (mol)
volume of solution (L)

26. 5.3 Concentration of Solutions
Example:
Practice Problem 12a, page 191
Do worksheet, BLM a, b, e

27. 5.3 Concentration of Solutions
Molar concentration of ions
Solving these always requires a dissociation or ionization equation
Example: calculate the molar concentration of each ion in mol/L Fe2(SO4)3
1 Fe2(SO4)3(s) Fe3+(aq) + 3 SO42(aq)
you will use this ratio often in Chapters 5, 7, and 8 (get used to it here)
“[ a ]” stands for molar concentration of a

28. 5.3 Concentration of Solutions
Example: Calculate the molar concentration of Ca3(PO4)2 required to produce a solution with [Ca2+]=0.425 mol/L
1 Ca3(PO4)2(aq) Ca2+(aq) + 2 PO3-(aq)
Do worksheet BLM 5.3.5A – answers on my website

29. 5.3 Concentration of Solutions
Molar concentration of ions in solution (continued)
Example: Practice Problem 17, page 193
1 Na2CO3(s) Na+(aq) + 1 CO32-(aq)
Do worksheet BLM , 5, 6
this looks like final answer, but need concentration of Na+, not solute

30. 5.3 Concentration of Solutions
Calculating mass from concentration and volume
Example: Practice Problem 23a, page 194
unit cancellation is better

31. 5.3 Concentration of Solutions
Calculating volume from mass and concentration
Example: Practice Problem 27b, page 195
Do worksheet BLM first side only

32. 5.4 Preparing and Diluting Solutions
standard solution: carefully made solution with known concentration
you’ll learn, in the lab, how to prepare a standard solution by 2 methods
Method 1: Preparation from solid – calculation already done (slide 27)

33. 5.4 Preparing and Diluting Solutions
Method 2: Preparation by Dilution
This is done for 2 possible reasons:
calculated mass of solute is too small to be weighed out
you may already have a more concentrated solution available and can prepare your by diluting the other

34. 5.4 Preparing and Diluting Solutions
Dilution calculation:
since in dilution, moles of solute can’t change, ni = nf
the dilution equation!

35. 5.4 Preparing and Diluting Solutions
Example: Practice Problem 31a, page 198
biggest problem students have with these is misidentifying the variables
I encourage you to list them:
ci = 1.25 mol/L
vi = ?
cf = 1.00 mol/L
vf = 50 mL
formulas with all multiplication are easy to rearrange
 do this 1st
units don’t have to “match”; as long as both v’s and both c’s have same units
Do worksheet BLM all

36. 5.4 Preparing and Diluting Solutions
Investigation 5.D – Solution Preparation and Dilution, page 200

37. 5.4 Preparing and Diluting Solutions
Chapter Review
Calculation Review: worksheet BLM 5.3.7

38. 5.4 Preparing and Diluting Solutions