A brief history


Properties of Acids
Sour taste
 Change color of vegetable dyes
 React with “active” metals (Corrosive)
 React with carbonates, producing CO
2
 React with bases to form ionic salts
Bases/Alkalis
 Taste bitter and feel slippery
 Change color of vegetable dyes
 React with acids to form ionic salts

Neutralization
3

Arrhenius Theory
 Acids ionize in water to form H +
(aq) cations and anions
 Bases dissociate in water to OH -
(aq) anions and cations
H +
(aq)
+ OH -
(aq)
 H
2
O
(l)
 H + ions are protons
4

Modern view: Say goodbye to H +
(aq) hydronium ion : H
3
O +
(aq)

H
( aq )

H
2
O
( l )

H
3
O
(
 aq )

Strong vs Weak Acids

A. Ionization of Water
H
2
O + H
2
O H
3
O + + OH -
[H
3
O + ][OH ] = 1.0

10 -14

A. Ionization of Water
 Find the hydroxide ion concentration of 3.0

10 -2 M HCl.
[H
3
O + ][OH ] = 1.0

10 -14
[3.0

10 -2 ][OH ] = 1.0

10 -14
[OH ] = 3.3

10 -13 M
Acidic or basic?
Acidic

B. pH Scale
0
INCREASING
ACIDITY
7
NEUTRAL pH = -log[H
3
O + ] pouvoir hydrogène (Fr.)
“hydrogen power”
INCREASING
BASICITY
14

B. pH Scale pH of Common Substances

B. pH Scale
3
+
-

B. pH Scale
 What is the pH of 0.050 M HNO
3
?
pH = -log[H
3
O + ] pH = -log[0.050] pH = 1.30
Acidic or basic?
Acidic

B. pH Scale
 What is the molarity of the SA HBr(aq) in a solution that has a pOH of 9.6?
pH + pOH = 14 pH + 9.6 = 14 pH = 4.4
Acidic
[H
3
O + ] = 10 -pH
[H
3
O + ] = 4.0

10 -5 M
HBr = 4.0

10 -5 M (SA)

pH & pOH calculations

SUMMARY

Practice
 6.2 Practice Questions pp. # 4-11
 6.2 Section Questions pp. # 4,6,8-10
 pH Worksheet

Acid Base Indicators
 What is it??

A substance that changes COLOUR when pH changes (so hydronium ion concentration is changing)

Acid-Base Indicator
Indicator changes colour @ endpoint.
Indicator is chosen so that endpoint occurs at equivalence pt.

6.4 Explaining Acids and Bases
 How can we explain why ammonia and sodium carbonate are basic??
 What about other chemicals…..CaO, CO
2
,
NaHSO
4
, NaHCO
3….
??

FIRST
HSO
4
-
(aq)
THEN

FIRST
THEN
CO
3
2-
(aq)

6.4 Explaining Acids and Bases
 TWO key ideas to remember when revising the Arrhenius definition of acid and base


1. Must consider collisions with H
2
O
2. The nature of the hydrogen ion
 for example:
HCl
(aq)
+ H
2
O
(l)
Cl -
(aq)
NH
3(aq)
+ H
2
O NH +
4(aq)
+ H
3
O +
(aq)
+ OH
–
(aq)

New Acid Base definitions

Neutralization
Special case of a double replacement reaction: acid and base forms water and a salt
Now we can define neutralization as a the reaction between hydronium and hydroxide ion

PRACTICE
 PQ ‘s #1-2 p.251
 Sec 6.4 Q’s #1-5 p.253

Acids and Bases

Strong vs Weak Acids
H
2
O + HNO
3

H
3
O + + NO
3
-
What makes an acid an acid??
…..ionization and formation of hydronium ions
What makes an acid strong or weak??
…..depends on the % ionization
99% - STRONG
(less than) < 99% - WEAK

Strong vs Weak Acids
H
2
O + HNO
3

H
3
O + + NO
3
SA
H
2
O + CH
3
COOH

H
3
O + + CH
3
COO WA

Strong vs Weak Bases
 Strong Bases - soluble ionic hydroxides.
They dissociate to release OH ions

NaOH
(aq)
Na +
(aq)
+ OH -
(aq)

Ba(OH)
2(aq)
Ba 2+
(aq)
+ 2OH -
(aq)

Strong vs Weak Bases
 Weak bases – react partially with water to create OHions and the “balancing entity”….general pattern e.g. CO
3
2-
(aq)
+ H
2
O OH + HCO
3
-

Polyprotic Acids
 Monoprotic acids – acids that have only one “acidic hydrogen atom” in their compound formula ….
general formula HA
 Polyprotic acids – acids that can react more than once with water so they have more than one “acidic hydrogen atom” in their compound formula ….
general formula H x
A

Polyprotic Acids - example

Polyprotic Bases
 Monoprotic bases – bases that react only once with water to produce hydroxide ions
….
 Polyprotic bases – bases that can react more than once with water but all reactions with the water are much less than 50% ….

Polyprotic Bases - example

In general
 Polyprotic acids are weak acids whose reaction with water decreases with each successive step
 Polyprotic bases are weak bases whose reaction with water decreases with each successive step

Summary
Do Section 6.5 questions 3-7,9 HWK

pH
  log[ H
3
O

] pOH
  log[ OH

]
K w

[ H
3
O

][ OH

]
[ H
3
O

]

K
[ OH w

]
[ OH

]

10
 pOH
[ H
3
O

]

10
 pH pH
 pOH
[ OH

]

[ H
K w
3
O

]

14 .
00

Given
[H
3
O + ]
[OH ] pH pOH
Using the Toolkit
Possible Action
• Convert [H
3
O + ]  [OH ]
• Convert [H
3
O + ]  pH
• Convert [OH ]  [H
3
O + ]
• Convert [OH ]  pOH
• Convert pH  [H
3
O + ]
• Convert pH  pOH
• Convert pOH  [OH ]
• Convert pOH  pH

[ OH

]

[ H
K
3 w
O

]

[ H
3
O

]

K w
[ OH

]

pH

14 .
00
 pOH

pOH

14 .
00
 pH

pH
  log[ H
3
O

]

pOH
  log[ OH

]

Chapter REVIEW
 Learning summary
 Chapter Review

Chap 6 Pt 1 – ALL
Pt 2 - #12,13,17-21

UNIT REVIEW
 Unit Review

Pt 1 – ALL

Pt 2 - #19, 22, 24, 26, 27, 30-32, 35