year 10-IGCSE

1. Acids, Bases, and pH
Glencoe: Chapter 24 Sections 3
and 4
Pages 764-774

2. I. What are acids?
 Substances that donate hydrogen ions, H+,
to form hydronium ions, H3O+, when
dissolved in water

3. Formation of Hydronium Ions
1+
hydronium ion
H3O+
+
hydrogen ion
H+
water
H2O
1+
(a proton)
1+

4. A. Characteristics of acids
1. Acids turn blue litmus paper red
 Litmus paper is an indicator
2. Acids taste sour
3. Can burn skin

5. Common Acids
Sulfuric Acid H2SO4
Nitric Acid HNO3
Phosphoric Acid H3PO4
Hydrochloric Acid HCl
Acetic Acid CH3COOH
Carbonic Acid H2CO3
Battery acid
Used to make fertilizers
and explosives
Food flavoring
Stomach acid
Vinegar
Carbonated water

6. B. Strong vs. Weak acids
1. Strong acids – ionize (break in to
cations and anions) almost completely,
and conduct electricity well
a. Nitric acid (HNO3)
b. Hydrochloric acid (HCl)
c. Sulfuric acid (H2SO4)
d. Perchloric acid

7. B. Strong vs. Weak acids
2. Weak acids – do not completely ionize
a. Acetic acid (vinegar)
b. Citric acid
c. ALL others

8. II. What are bases?
- Substances that form hydroxide ions (OH-
)
ions when in water, or accept H+ ions

10. A. Characteristics of Bases
1. Taste bitter
2. Slippery
3. Bases turn red
litmus paper blue
4. Can burn skin

11. B. Strong vs. Weak bases
1. Strong bases - ionize (break into
cations and anions) almost completely,
and conduct electricity well
a. KOH – potassium hydroxide
b. NaOH – sodium hydroxide
2. Weak bases - do not completely ionize
a. Ammonia (NH3)

12. Review
 Acid: A solution that has an excess of H+
ions. It comes from the Latin word acidus
that means "sharp" or "sour".
 Base: A solution that has an excess of OH-
ions. Another word for base is alkali.
 Aqueous: A solution that is mainly water.
Think about the word aquarium. AQUA
means water.

13. III. Why is a substance neutral?
 A substance is neutral when:
1. It does not ionize at all, therefore no
H+ or OH- ions
2. It has equal concentrations
(amounts) of H+ and OH- ions

14. IV. How acidic or basic is it?
A. pH – measures the concentration of H3O+
ions
 Crowded
Not Crowded 
 More crowded = More concentrated
 Critical to certain processes and functions
- example: enzymes, blood
B. pH  indicates H3O+ and OH- concentrations

15. Concentration vs. Strength
 Concentration is not the same as strength
 Concentration deals with the amount of
hydronium ions in the solution, compared to
the amount of water in the solution.
 More acid or base and less water
= more concentrated
 More ions and less molecules
= stronger

17. III. How acidic or basic is it?
C. pH scale  0-14
 Indicates concentration of hydronium ions
0-6 = acid  closer to 0 is more acidic
8-14 = base  closer to 14 is more basic
7 = neutral  H3O+ concentration = OH-
concentrations

19. III. How acidic or basic is it?
D. Each pH unit = a power of ten
- Example: pH 3 is 100 times more
acidic than pH 5

20. Review
 Strong Acid: An acid that has a very low pH (0-4).
 Strong Base: A base that has a very high pH (10-14).
 Weak Acid: An acid that only partially ionizes in an
aqueous solution. That means not every molecule
breaks apart. They usually have a pH close to 7 (3-6).
 Weak Base: A base that only partially ionizes in an
aqueous solution. That means not every molecule
breaks apart. They usually have a pH close to 7 (8-10).
 Neutral: A solution that has a pH of 7. It is neither
acidic nor basic.