Chemistry Form 4 KSSM Chapter 6 Acid, Base and Salt

1. CHAPTER 6
ACID, BASE AND SALT
PREPARED BY : ESTHER ANNE ANAK RANDI

2. Chapter 6 Acid, Base and Salt
6.1 Role of water in showing acidic and alkaline
properties.
6.2 pH value
6.3 Strength of acids and alkalis
6.4 Chemical properties of acids and alkalis
6.5 Concentration of aqueous solutions
6.6 Standard solution
6.7 Neutralisation
6.8 Salts, crystals and their uses in daily life
6.9 Preparation of salts
6.10 Effect of heat on salts
6.11 Qualitative analysis

3. 6.1 ROLE OF WATER IN SHOWING
ACIDIC AND ALKALI PROPERTIES

4. Learning Standards
Pupils are able to :
6.1.1 Define acids and alkalis
6.1.2 State the meaning of basicity of an acid
6.1.3 Investigate the role of water in showing acidic and alkaline
properties through experiment

5. Learning Objectives
A student is able to :
 State the meaning of acid, base and alkali
 State uses of acids, bases and alkalis in daily life
 Explain the role of water in the formation of hydrogen ions
to show the properties of acids
 Explain the role of water in the formation of hydroxide ions
to show the properties of alkalis

6. Acid
• When acid is dissolved in water, the hydrogen atoms in acid
molecules are released in the form of hydrogen ions, H+.
• Based on the Arrhenius theory, acid is defined as :
Acid is a chemical substance that ionises in water to
form hydrogen ions, H+.

7. • When hydrogen chloride gas is dissolved in water, hydrogen chloride
molecules will ionise in water to produce hydrogen ions, H+ and
chloride ions, Cl– .
• However, do the hydrogen ions, H+ remain in the aqueous solution?

8. • Hydrogen ions, H+ produced will combine with the water
molecules, H2O to form hydroxonium ions, H3O+.

9. Basicity of Acids
• Basicity of acids refers to the
• Hydrochloric acid, HCl is monoprotic acid because it can
produce one hydrogen ion, H+ per acid molecule.
The number of hydrogen ions, H+ that can be
produced by an acid molecule that ionises in water.
HCl  H+ + Cl-

10. Monoprotic acid
HCl  H+ + Cl-
Monoprotic acid
produces one H+ ion
per acid molecule

11. Diprotic acid produces
two H+ ion per acid
molecule
Diprotic acid
H2SO4  2H+ + SO4
2-

12. Triprotic acid produces
three H+ ion per acid
molecule
Triprotic acid
H3PO4  3H+ + PO4
3-

13. Monoprotic acid
HCl  H+ + Cl-
Diprotic acid
H2SO4  2H+ + SO4
2-
Triprotic acid
H3PO4  3H+ + PO4
3-

14. Examples of acid and their basicity
Ionisation of acid
Number of hydrogen ions
produced per molecule of acid
Basicity of acid
HNO3  H+ + NO3
- One Monoprotic
H2SO4  2H+ + SO4
2- Two Diprotic
H3PO4  3H+ + PO4
3- Three Triprotic
*CH3COOH  H+ + CH3COO- One Monoprotic
*Ethanoic acid = double headed arrow
Indicating that not all hydrogen atoms in ethanoic acid are ionisable

15. PROPERTIES OF ACID
1. Tastes sour
2. Changes blue litmus paper to red
3. pH value less than 7
4. Corrosive

16. Base
• Base is a substance that reacts with acids to produce salt
and water ONLY.
• Most bases are Metal oxides and metal hydroxides.
• Metal oxides : Copper(II) oxide, CuO; sodium oxide, Na2O
• Metal hydroxides : Zinc hydroxide, Zn(OH)2; potassium
hydroxide, KOH

17. • Copper(II) oxide (a base) reacts with sulphuric acid to produce
copper(II) sulphate (a salt) and water.
• Zinc hydroxide (a base) reacts with hydrochloric acid to produce zinc
chloride (a salt) and water.
CuO + H2SO4  CuSO4 + H2O
Zn(OH)2 + 2HCl  ZnCl2 + 2H2O
Metal oxide
(base)
Acid Salt Water
Metal
hydroxide
(base)
Acid Salt Water

18. Base
• A base that is soluble in water is called an alkali.
• Potassium hydroxide, KOH and sodium hydroxide,
NaOH are alkalis because they are soluble in water.

19. Base
• When sodium hydroxide pellets, NaOH is dissolved in
water, sodium ions, Na+ and hydroxide ions, OH–
that can move freely in water are produced.

20. Alkali
• An alkali is defined as follows :
• Sodium hydroxide dissolves in water and ionises to
produce hydroxide ions, OH-
• Other examples of alkalis are barium hydroxide and
calcium hydroxide.
A chemical substance that ionise in water to produce
hydroxide ions, OH-.
NaOH  Na+ + OH-

21. Alkali
• Ammonia is NH3
• What will happen to ammonia molecule when
ammonia gas is dissolved in water?

22. Alkali
• By dissolving ammonia gas in water, aqueous
ammonia is produced.
• Aqueous ammonia is an alkali because the ammonia
molecules ionise partially to produce hydroxide ions,
OH–.

23. *Sodium hydroxide and potassium hydroxide are soluble in
water and they are called alkali whereas magnesium oxide and
zinc oxide are called bases as they are insoluble in water.
Soluble base (alkali) Insoluble base
Name Formula Ionisation equation Name Formula
Sodium oxide Na2O
Na2O + H2O  2NaOH
NaOH  Na+ + OH- Copper(II) oxide CuO
Potassium oxide K2O
K2O + H2O  2KOH
KOH  K+ + OH- Copper(II) hydroxide Cu(OH)2
Ammonia NH3 NH3 + H2O  NH4
+ + OH- Zinc hydroxide Zn(OH)2
Sodium hydroxide NaOH NaOH  Na+ + OH- Aluminium oxide Al2O3
Potassium hydroxide KOH KOH  K+ + OH- Lead(II) hydroxide Pb(OH)2
Barium hydroxide Ba(OH)2 Ba(OH)2 Ba2+ + 2OH- Magnesium hydroxide Mg(OH)2

24. Properties of Alkali
1. Tastes bitter
2. Feels slippery
3. Changes litmus paper from red to blue
4. pH value greater than 7
5. Corrosive

25. Uses of Acids, Bases and Alkalis
• Acids, bases and alkalis are not just chemical substances in the
laboratory but they are also widely found in daily life.
• Toothpaste which is alkaline, functions to neutralise acid on
the teeth, while vinegar is an acidic substance used to make
pickled chillies.

26. Activity 6.1 Discussing the uses of acids and alkalis in daily life using
examples of acidic and alkaline substances
1. Choose any TWO fields from the following
2. Gather information from reading materials or websites on examples
of acidic or alkaline substances as well as their uses in the field
chosen.
3. Based on the information gathered :
– Identify the acid, base or alkali in each substance that you have found
– State the uses of acid, base or alkali found in the substance

27. Uses of Acids in Daily Life
• Acids and bases are widely used in our daily life in agriculture,
medicine, industry and preparation of food
Sulphuric acid in
Lead-acid accumulator
Tartaric acid in
Baking powder
Nitric acid in
Plant fertilizers

28. Uses of Bases in Daily Life
• Acids and bases are widely used in our daily life in agriculture,
medicine, industry and preparation of food
Sodium hydroxide in soaps
and detergents
Magnesium hydroxide in
toothpaste
Aluminium hydroxide
in gastric medicine

29. TEST YOURSELF
1. State the meaning of the following terms :
1. Acid
2. Base
3. Alkali
2. Carbonic acid is a mineral acid with the formula, H2CO3.
What is the basicity of carbonic acid? Explain why.
3. Give 1 example of uses of acid and alkali in our daily
lives.