1. Acids, Bases and Salts
1

2. Acids
Definition: Acids are chemical substances
that produces hydrogen ions as the only
positively charged ion when dissolved in
water
 Acids taste sour
 pH < 7
 Corrosive
 Conducts electricity when aqueous
 Turns blue litmus paper red
2

3. Acids: Strong or weak?
Strong acid Weak acid
 
Ionizes completely in water Ionizes partially in water
 
Produces a lot of H+ ions Produces little H+ ions
 
All acid molecules form ions Not all acid molecules form ions
 
Very corrosive Not so corrosive
 
Mineral acids Organic acids
 
Strong electrolyte Weak electrolyte
 
3

4. Complete Ionisation in SA
Cl-
H+
Cl
H
Cl
Cl
-
H
H
H+
Cl-
Cl
H
Cl
-
Cl
+
H
H+
–
HCl  H + Cl +
4

5. Partial Ionisation of WA
CH3COO H
CH3COO H
H
CH3COO
H
CH3COO
CH
CH
C OO
3
CO +
H
3
O-
H
H
H
OO
OO C
C
CH
3
CH
3
CH3COOH  H+ + CH3COO–
5

6. Strong Acids
 Hydrochloric acid, HCl
 Sulphuric acid (UK); Sulfuric acid (US),
H2SO4
 Nitric acid, HNO3
6

7. Weak Acids
 Natural acids/Food acids
 Ethanoic/Acetic acid (Found in
vinegar)
 Citric acid (Found in
lime/lemon)
 Malic acid (Found in apple)
7

8. Reactions of Acids
with Reactive Metals
 Acid + Metal  Salt + Hydrogen
 Eg.
Hydrochloric acid + Zinc

 Zinc chloride + Hydrogen
Not applicable to non-reactive metals like
copper, silver and gold…
8

9. Reactions of Acids
with Metal Carbonates
 Acid + Metal Carbonate
 Salt + Carbon Dioxide + Water
 Eg.
Hydrochloric Acid + Sodium carbonate
 Sodium chloride +
carbon dioxide + water
9

10. Bases
Definition: A class of chemical substances
which include all metal oxide, hydroxides,
ammonium oxide and hydroxides
 Calcium oxide – quicklime
 Calcium hydroxide – limewater
 Sodium hydroxide
 Magnesium oxide etc…
10

11. Alkali
Definition: An alkali is a soluble base that produces
hydroxide ions as the only negatively charged
ions when dissolved in water
 Feel soapy to touch
 Taste bitter
 pH > 7
 Corrosive
 Conduct electricity when aqueous
 Turn red litmus paper blue
11

12. Reaction of Alkali
with Ammonium Salts
 Alkali + Ammonium Salt
 Salt + Ammonia + Water
 Eg.
Sodium hydroxide + Ammonium chloride
 Sodium chloride + Ammonia + Water
12

13. Neutralization
 Acid + Base  Salt + Water
 Eg.
Hydrochloric acid + Sodium hydroxide
 Sodium chloride + Water
Ionic equation for acid-alkali neutralization:
H+ (aq) + OH– (aq)  H2O (l)
13

14. Salts
Definition: A salt is the substance formed
when the hydrogen of an acid is partially
or totally replaced by a metal
14

15. Basicity
 The number of hydrogen atoms in an acid
that can be replaced by a metal is called
Basicity
 Eg. Hydrochloric acid with 1 hydrogen
atom is monobasic
 Sulphuric acid with 2 hydrogen atoms is
dibasic
 Phosphoric acid with 3 hydrogen atoms is
tribasic
15

16. Acid Salts
 Definition: Only part of the hydrogen
present in the acid is replaced by a metal
 Eg. Sodium hydrogensulphate
 Sodium hydrogencarbonate, Baking soda
16

17. Uses
 Salts are used in chemicals, soaps &
detergents, photography, food &
flavourings, medical uses, paints and
fertilizers, etc…
 Eg. Ammonium nitrate used as a fertilizer,
Zinc sulphide in luminous paints, sodium
fluoride in toothpaste, barium carbonate
as a rat poison, calcium sulphate used as
plaster
17

18. Indicators
 Definition: Indicators are dyes, or mixtures
of dyes, which changes colour when acids
or alkalis are added to them
18

19. Indicators
19

20. Power of Hydrogen
When pH decreases, the concentration of

hydrogen ions increases.
When pH increases, the concentration of

hydrogen ions decreases.
pH values lesser than 7, shows that it is acidic.

More hydrogen ions than hydroxide ions.
pH values greater than 7 shows that it is

alkaline. More hydroxide ions than hydrogen
ions.
At pH 7, it is neutral. Hydrogen and hydroxide

ions are in equal concentration.
20

21. Types of Oxides
 Basic oxides
 Amphoteric oxides
 Acidic oxides
 Neutral oxides
21

22. Basic Oxides
Oxides of metals

Mostly insoluble in water – refer to solubility

table
Soluble basic oxides will dissolve in water to

form alkalis
Sodium oxide dissolves readily in water to for sodium

hydroxide
Reacts with acids and undergoes neutralization

reactions
Eg. Copper(II) oxide, calcium oxide, magnesium

oxide
Does not react with bases

22

23. Amphoteric Oxides
Oxides of metals that react with both acids and

bases
Eg. ZnO + 2HCl  ZnCl2 + H2

In the presence of acid, the amphoteric oxide

behaves like a base
ZnO + 2NaOH  Na2ZnO2 + H2O

In the presence of alkali, the amphoteric oxide

behaves like an acid
Others include aluminium oxide and lead(II)

oxide and lead(IV) oxide
23

24. Acidic Oxides
 Oxides of non-metals
 Soluble in water to produce acids
 Eg. CO2 + H2O  H2CO3
 Acidic oxides reacts with alkalis and
undergoes neutralization reactions
 Eg. Sulfur dioxide, sulfur trioxide, nitrogen
dioxide, phosphorus(V) oxide
 Does not react with acids
24

25. Neutral Oxides
 Oxides of non-metals
 Insoluble in water
 Will not react with acids nor bases
 Eg. Water, carbon monoxide, nitrogen
monoxide
25

26. Water of crystallization
26

27. Hydrated salts
 Salts that contain water of crystallization
 Eg. Hydrated copper(II) sulphate
 Chemical formula: CuSO4.5H2O
 Crystalline solid held together by water
molecules to form crystals
 Salts without water of crystallization are
called anhydrous salts
 Water of crystallization can be removed by
heating, water is driven off
27