1. Acid and bases
Bases

2. Prior knowledge

3. What happened the tooth?
Our teeth is composed of calcium carbonate.
Recall: Acids react with metal carbonates to give salt, water and carbon dioxide.

4. What will we learn today?
What is a base?
What are alkalis?
Physical properties of alkalis?
Chemical properties of alkalis?
Characteristics and properties of the Universal indicator.

5. Bases
A base is a substance that reacts with an acid to form salt and water only.
General equation ( acid + base) Base acid  Salt Water
Recall: Metal oxides and metal hydroxides are examples of bases.
An alkali is a base that is soluble in water
This is the main focus

6. Examples of bases Bases (metal oxides and hydroxides)
Bases that are soluble in water (alkalis)
Bases that are insoluble in water
Sodium oxide, Na2O
Magnesium oxide, MgO
Potassium oxide, K2O
Magnesium hydroxide, Mg(OH)2
Sodium hydroxide, NaOH
Zinc oxide, ZnO
Potassium hydroxide, KOH
Copper(II) oxide, CuO
Ammonia solution, NH3(aq)

7. Physical Properties of alkalis
Bitter taste
Soapy feel
Turn red litmus paper blue.
Turn Universal indicator Blue/violet
Alkali

8. Chemical properties of alkalis (I)
Alkalis react with acids to form a salt and water.
This reaction is known as neutralisation.
Example NaOH(aq) HCl(aq)  NaCl(aq) + H2O(l)
H+(aq) +OH-(aq) H2O(l)
Sodium hydroxide
Hydrochloric acid
Sodium chloride
Water

9. Chemical properties of alkalis (II)
Alkalis produce hydroxide ions when dissolved in water.
Example NaOH(aq)  Na+(aq) + OH-(aq)
Sodium hydroxide
Sodium ions
Hydroxide ions

10. Chemical properties of alkalis (III)
Alkalis, when heated with ammonium salts, releases ammonia gas.
Example NaOH(aq) + NH4Cl(s) NaCl(aq) +H2O(l) +NH3(g)
Heat

11. Chemical properties of alkalis (IV)
Alkalis react with some salt solution to form precipitates of metal hydroxides.
Example 2NaOH(aq) + FeSO4(aq)  Fe(OH)2(s) +Na2SO4(aq)

12. Strong Acid vs Weak Acid

13. Strong acid
Strong acid is one that undergoes complete dissociation to form ions in water.
In a solution of strong acid, all the acid molecules dissociate to become ions in water.
Examples Sulfuric acid, Hydrochloric acid, Nitric acid

14. Weak acid
Weak acid is one that undergoes partial dissociation to form H+ ions in water.
In a solution of a weak acid, few acid molecules dissociate to become ions in water. (Most of the acid molecules remain as acid molecules in water.)
Examples Ethanoic acid, Citric acid

15. The pH scale
The pH scale is used to illustrate if a solution is acidic, neutral or alkaline.
The pH scale ranges from 0 to 14.
The lower the pH value of a solution the more acidic it is.
The higher the pH value of a solution the higher is its alkalinity.

16. Understanding the scale
Neutral
Strong acids
e.g. HCl
weak alkalis
e.g. NH3(aq) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Acidity increases
<<<<<<<<<<<<<
Alkalinity increases
>>>>>>>>>>>>>>>
Thinking point
What is the pH range for acidic solutions?
What is the pH range for alkaline solutions?
What is the pH/ pH range for neutral solutions?
What can be a possible value of a strong acid and weak alkali?

17. Universal indicator
An universal indicator measures the pH of a solution.
A different pH would result in a different colour change for the universal indicator.
yellow
Bluish-green 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Red
Orange
blue
Purple
Green

18. A coloured version

19. What have we learnt today?
What is a base?
The chemical properties of bases.
The physical properties of bases.
The neutralisation process.
Characteristics and properties of the universal indicators.