1. Chemistry 20 Chapter 6 – Acids and Bases
PowerPoint Presentation by R. Schultz

2. 6.1 Theories of Acids and Bases
Acids and Bases at home:
chart page 208

3. 6.1 Theories of Acids and Bases
Nomenclature
Bases have no special nomenclature
Acid nomenclature:
New IUPAC nomenclature – name the compound as if it was ionic adding the word “aqueous” in front
examples:
HCl(aq)
H2SO4(aq)
aqueous hydrogen chloride
aqueous hydrogen sulfate
this method is relatively new and still not commonly used by chemists

4. 6.1 Theories of Acids and Bases
Classical acid nomenclature
Start by naming the compound as it was ionic
Look at ending and apply following rules
__________ide  hydro_______ic acid
__________ate  __________ic acid
__________ite  __________ous acid

5. 6.1 Theories of Acids and Bases
Example: Consider the following group of acids:
Formula
Name (if it was ionic)
Classical Acid
Name
put the word “aqueous” in front and you’ve got the IUPAC name HC l ( aq )
rule 1
hydrogen
chloride
hydrochloric acid HC l O ( aq )
rule 2
hydrogen
perchlorate
perchloric
acid 4 HC l O ( aq )
rule 2
hydrogen chlorate
chloric
acid 3
rule 3 HC l O ( aq )
hydrogen
chlorite
chlorous
acid 2
rule 3 HC l O ( aq )
hydrogen hypochlorite
hypochlorous
acid

6. 6.1 Theories of Acids and Bases
2 elements to be careful about: S and P
both keep the middle syllable in classical acid nomenclature H2SO4(aq) “sulfuric acid”, not “sulfic acid” H3PO4(aq) “phosphoric acid”, not “phosphic acid”
Quiz next day – same format as practice quiz you’ll do now
After quiz you won’t need to know classical acid nomenclature by memory as the names and formulae of many acids are in your Data Booklet, pages 8 and 9

7. 6.1 Theories of Acids and Bases
acids and bases can be defined empirically (in terms of properties) or theoretically (in terms of theories that explain their properties)
chart page 210

8. 6.1 Theories of Acids and Bases
Explaining (theories)
Arrhenius acid: ionizes in water to produce H+(aq) base: dissociates in water to produce OHˉ(aq)
according to Arrhenius’ theory, acid formulas must contain H and base formulas must contain OH
do Investigation 6.B to test this out

9. 6.1 Theories of Acids and Bases
problems from lab: NH3(aq) was basic, NaHCO3(aq) was basic, others??
Arrhenius’ theory worked well for many, but not all acids and bases
Slight modifications provide great improvement

10. 6.1 Theories of Acids and Bases
revised or modified Arrhenius theory:
acid: reacts with water to produce hydronium ion, H3O+(aq)
before: HCl(aq) H+(aq) + Clˉ(aq)
now: HCl(aq) + H2O(l) H3O+(aq) + Clˉ(aq)
base: dissociates or reacts with water to produce OHˉ(aq)
before: NaOH(s) Na+(aq) + OHˉ(aq)
now: exactly the same

11. 6.1 Theories of Acids and Bases
Here’s where the benefit comes:
NH3(aq):
before: NH3(aq) ???????
now: NH3(aq) + H2O(l) NH4+(aq) + OHˉ(aq)
now NH3’s basic behaviour is explained
NaHCO3(aq):
NaHCO3(s) Na+(aq) + HCO3ˉ(aq), then, HCO3ˉ(aq) + H2O(l) H2CO3(aq) + OHˉ(aq)
now NaHCO3’s basic behaviour is explained

12. 6.1 Theories of Acids and Bases
Try a weird acid like CO2(aq) (soda water)
standard Arrhenius theory doesn`t explain
Revised:
CO2(g) + H2O(l) H2CO3(aq), then,
H2CO3(aq) + H2O(l) HCO3ˉ(aq) + H3O+(aq)
oxides will always be 2 steps – metal oxides to produce bases; non-metal oxides to produce acids
Worksheet BLM 6.1.0

13. 6.2 Strong and Weak Acids and Bases
terms: “strong acid” and “weak acid” have technical meaning – they are based on identity, not acidic behaviour
note that at both 1.0 mol/L and mol/L HCl(aq) is more reactive than CH3COOH(aq)
fig 6.7 page 218

14. 6.2 Strong and Weak Acids and Bases
Strong acid: reacts 100% with water or 100% ionized in water
HCl(aq) + H2O(l) H3O+(aq) + Clˉ(aq)
strong acids are the 1st 6 acids listed in your chart, page 8-9 of the Data Booklet
fig 6.8, page 219

15. 6.2 Strong and Weak Acids and Bases
Weak Acid: reacts only partially (usually very weakly) with water or ionizes only partially
CH3COOH(aq) + H2O(l)  H3O+(aq) + CH3COOˉ(aq)
weak acids are all the others
fig 6.9 page 220
do worksheet BLM 6.2.4

16. 6.2 Strong and Weak Acids and Bases
Is it possible for a strong acid to be less acidic in behaviour than a weak acid?
strong bases and weak bases:
aqueous ionic hydroxides and ionic oxides are strong bases
all other bases (from Data Booklet page 8-9 “Conjugate Base” column) are weak
yes, if its concentration is very low and the weak acid’s concentration is very high
read about “weak acids and bases” page 221 bottom and page 223 bottom
discuss questions 5-7, page 222

17. 6.2 Strong and Weak Acids and Bases
Mono and polyprotic acids
monoprotic acids: have only 1 hydrogen atom that reacts to produce H3O+(aq), e.g. HCl(aq), HBr(aq), HNO3(aq)
polyprotic acids: have 2 or more hydrogen atoms that react to produce H3O+(aq), e.g. H2SO4(aq) (diprotic), H3PO4(aq)  (triprotic)

18. 6.2 Strong and Weak Acids and Bases
in a series of acids, one with most H’s is strongest
e.g. H3PO4(aq)
H3PO4(aq) + H2O(l)  H3O+(aq) + H2PO4ˉ(aq)
H2PO4ˉ(aq) + H2O(l)  H3O+(aq) + HPO42ˉ(aq)
HPO42ˉ(aq) + H2O(l)  H3O+(aq) + PO43ˉ(aq)
H3PO4(aq) > H2PO4ˉ(aq) > HPO42ˉ(aq)
strongest weakest

19. 6.2 Strong and Weak Acids and Bases
mono and polyprotic bases
monoprotic base: reacts with water or ionizes to produce 1 OHˉ(aq) e.g. NaOH(aq), NH3(aq)
polyprotic base: reacts with water or ionizes to produce 2 or more OHˉ(aq)
e.g. CO32ˉ(aq), HPO42ˉ(aq)
in a series of bases, one with the least H’s is most basic:
PO43ˉ(aq) > HPO42ˉ(aq) > H2PO4ˉ(aq)
strongest weakest

20. 6.2 Strong and Weak Acids and Bases
Read pages
neutralization reaction:
acid + base water + a salt
neutral ionic compound
e.g. NaOH(aq) + HNO3(aq) H2O(l) + NaNO3(aq)
net ionic equation for all strong acid/strong base neutralizations:
H3O+(aq) + OHˉ(aq) H2O(l)

21. 6.3 Acids, Bases and pH
all aqueous solutions contain both H3O+(aq) and OHˉ(aq) ions If [H3O+] is high, [OHˉ] is low
following slide illustrates their relationship in aqueous solutions
note: to fit this comfortably on 1 page, I have used H+(aq) instead of H3O+(aq), recognizing that they both represent same chemical entity

22. 6.3 Acids, Bases and pH example [H+]: pH= 1 3 5 9 11 13 7
10-1 mol/L
10-3 mol/L
10-5 mol/L
10-7 mol/L
10-9 mol/L
10-11 mol/L
10-13 mol/L
acidic
basic
pH= 7
corresponding [OHˉ]:
10-13 mol/L
10-11 mol/L
10-9 mol/L
10-7 mol/L
10-5 mol/L
10-3 mol/L
10-1 mol/L

23. 6.3 Acids, Bases and pH
fig 6.17, page 230

24. 6.3 Acids, Bases and pH H2O(l) + H2O(l)  H3O+(aq) + OHˉ(aq)
water is an extremely weak acid; [H3O+]=[OHˉ]=1.0 x 10-7 mol/L
also, [H3O+]=[OHˉ]=1.0 x 10-7 mol/L in any neutral solution
In previous slide if [H3O+] = 10ˉ9 mol/L, pH equaled 9
formula: pH = -log [H3O+] or pH = -log [H+]

25. 6.3 Acids, Bases and pH log is a function on your calculator
log of a # is the power of 10 you’d need to get the #
based on this, what is log 100 (no calculator)?
log 1000?
log 0.1? 2 3 -1

26. 6.3 Acids, Bases and pH
log (10ˉ7 mol/L)=-7 (try it on your calculator)
Why do you think pH = - log [H3O+]?
Discuss
should look like this
or you could enter like this

27. 6.3 Acids, Bases and pH
Try the following exercise (write your answers):
-log (1.89x10ˉ9) (enter as 1.89E-9)
-log(1.89x10ˉ8)
-log(1.89x10ˉ7)
-log(1.89x10ˉ6)
this part is related to the 1.89
this part is related to the power of 10
significant digits
not significant
if [H3O+] = 1.89 x 10-6 mol/L, pH = !

28. 6.3 Acids, Bases and pH
General rule: when finding pH from concentration, number of significant digits in concentration is same as the number of decimal places in pH! (this is rule 4 on significant digits handout!)
When finding concentration from pH, number of decimal places in pH is same as significant digits in concentration

29. 6.3 Acids, Bases and pH What is meaning of pH increase by 2 units?
Examples: Practice Problems 1a, 1c page 230
1a)
1c)
Do worksheet BLM questions 1, 2, 5, 6, 9, 10a
[H3O+] has decreased by 100 times

30. 6.3 Acids, Bases and pH Measuring pH – indicators and pH meters
Indicators: substances whose colour changes with pH
page 10, Data Booklet:
shorthand formulas
here’s a few; fig 6.18, page 231
HMr(aq)/Mrˉ(aq)
HBb(aq)/Bbˉ(aq)
HIc(aq)/Icˉ(aq)

31. 6.3 Acids, Bases and pH
Examples: following indicators are added to fresh samples of a solution. Results given. Estimate pH.
indicator
colour
methyl violet
blue
methyl orange
yellow
methyl red
red
phenolphthalein
colourless
pH > 1.6
pH > 4.4
pH < 4.8
pH < 8.2
conclusion: pH 4.4 – 4.8

32. 6.3 Acids, Bases and pH Try this one: indicator colour indigo carmine
blue
phenol red
yellow
bromocresol green
methyl orange
orange
pH < 11.4
pH < 6.6
pH < 3.8
pH 3.2 – 4.4
conclusion: pH 3.2 – 3.8
do worksheet BLM 6.3.6
Investigation 6.D, page 232

33. 6.3 Acids, Bases and pH
Demonstration: Investigation 6.E, page 234

34. 6.3 Acids, Bases and pH
pH after dilution – note can’t raise pH of an acid to > 7 by dilution (since water already has [H3O+] = 10ˉ7 mol/L)
can’t lower pH of a base to < 7 by dilution
(since water already has [OHˉ] = 10ˉ7 mol/L)

35. 6.3 Acids, Bases and pH
Example: A 35.0 mL sample of mol/L HCl(aq) is diluted to 300 mL
What is pH of the concentrated solution?
What is concentration of diluted solution?
pH of diluted solution?
do worksheet BLM #2, 3, 4

36. 6.3 Acids, Bases and pH pOH = -log [OHˉ] (like pH, but for OHˉ)
you haven’t heard of pOH because it’s never measured or reported – it’s calculated and used as a calculation tool because ………..
pOH is opposite to pH – it’s low for bases and high for acids (see table 6.8, page 237)
pH + pOH = 14.00

37. 6.3 Acids, Bases and pH Further formulas:
[H3O+] = 10ˉpH [OHˉ] = 10ˉpOH
Examples:
Practice Problem 13a, page 241
2 ways to enter:
1 significant digit
a) type “10^-3.9”
b) Do “2nd log” then enter -3.9

38. 6.3 Acids, Bases and pH Practice Problem 13d, page 241
What is the pOH of a mol/L solution of barium hydroxide, Ba(OH)2?
Ba(OH)2(s) Ba(OH)2(aq) Ba2+(aq) + 2 OHˉ(aq)

39. 6.3 Acids, Bases and pH
What is the concentration of sodium hydroxide, NaOH(aq), that gives a solution with a pH of 10.32?
since it’s a base start by finding pOH
Since NaOH dissociates as
NaOH(s) Na+(aq) + OHˉ(aq),
[NaOH]=2.1x10-4 mol/L

40. 6.3 Acids, Bases and pH
Example: What mass of rubidium hydroxide, RbOH(s), needs to be dissolved in 1.50 L of water to create a solution with a pH of 9.35?
Do worksheet BLM questions 1a, 2a, 3, 4, 6, 7, 8
RbOH(s) → RbOH(aq) → Rb+(aq) + OH‾(aq)

41. 6.3 Acids, Bases and pH Putting it all together:
Worksheet BLM question 1, 3, 4, 6, 7

42. 6.3 Acids, Bases and pH
Chapter Review:
Worksheet BLM

43. 6.3 Acids, Bases and pH