Acids and alkalis have distinct properties. Acids have a sour taste and turn litmus paper red, while alkalis have a bitter taste and turn litmus paper blue. An acid produces hydrogen ions in water, giving it corrosive properties, while an alkali produces hydroxide ions. Common acids include citric acid and sulfuric acid, while common alkalis include sodium hydroxide and calcium hydroxide. Acids react with metals to produce salts and hydrogen gas, with carbonates to produce salts, carbon dioxide, and water, and with alkalis to produce salts and water through a neutralization reaction.

1. Acids and
Alkalis
Physical and Chemical
Properties

2. Properties of Acids
1. Acids have sour taste.
2. Acids are corrosive.
3. Acids dissolve in water to form solutions
which conduct electricity.

3. Acids in Food
o Citric acid (in lemons)
o Ethanoic acid (in vinegar)
o Carbonic acid (in soft drinks)
o Tartaric acid (in grapes)
o Malic acid (in apples)
o Lactic acid (in yoghurt)
Weak
organic acids
found in food

4. An acid is a substance which produces
hydrogen ions when it is dissolved in water.
The hydrogen ions give an acid its acidic
properties.
Acids only behave as acids when they are
dissolved in water.
What is an Acid?

5. TAKE NOTE
NOT all substances that contain
hydrogen are acids.
For example,
•NH3 (ammonia) contains hydrogen but it is not
an acid.
•H2 (hydrogen) is also not an acid.

6. Properties of Alkalis
1. Alkalis have bitter taste.
2. Alkalis have soapy feel.
3. Alkalis dissolve in water to form solutions
which conduct electricity.

7. • An alkali is a substance
which produces
hydroxide ions when it is
dissolved in water.
• The hydroxide ions,
OH-
(aq) give an alkali its
alkaline properties.
• Alkalis only behave as
alkalis when they are
dissolved in water.
What is an Alkali?

8. An acid is a substance which produces hydrogen
ions when it is dissolved in water.
Summary
What is an acid?
Hydrochloric acid, sulfuric acid, nitric acid,
ethanoic acid, citric acid …
Examples of acids?

9. An alkali is a substance which produces
hydroxide ions when it is dissolved in water.
Summary
What is an alkali?
Sodium hydroxide, potassium hydroxide,
calcium hydroxide, aqueous ammonia
Examples of alkalis?

10. Indicators
o An indicator is a substance which changes colour
depending on whether the solution tested is acidic or
alkaline.
o There are many types of indicators, including the
universal indicator and litmus indicator.

11. Litmus Indicator
• Acids turn blue litmus paper red.
o Litmus paper exists in two colours, red and blue.
• Alkalis turn red litmus paper blue.

12. Acids + Metals
Acids react with some metals to form a salt and
hydrogen gas.
hydrochloric
acid magnesium
magnesium
chloride
hydrogen
gas
+  +
sulfuric acid magnesium
magnesium
sulfate
hydrogen
gas
+  +
1
Acid + Metal  Salt + Hydrogen gas

13. Acids + Metals
 The type and name of salt depends on the acid used.
Reaction with
• Hydrochloric acid 
• Sulfuric acid 
• Nitric acid 
Chloride salts
Sulfate salts
Nitrate salts

14. Acids + Metals
Acids react with some metals to form a salt and
hydrogen gas.
Some metals which can react with acids are magnesium,
aluminium, zinc and iron.
Explosive reactions occur when using reactive metals like
lithium, sodium and potassium.
Exception:
Unreactive metals such as copper and silver do not react
with dilute acids.

15. Acids + Metals
How to test for hydrogen gas?
 Place a lighted splint in the presence of the gas.
 If hydrogen is present, the lighted splint will be
extinguished with a ‘pop’ sound.

16. Acids + Carbonates
Acids react with carbonates to form a salt, carbon
dioxide gas and water.
2
hydrochloric
acid
sodium
carbonate
sodium
chloride
carbon
dioxide
gas
+  +
nitric acid calcium
carbonate
calcium
nitrate
+ 
water+
carbon
dioxide
gas
+ water+
Acid + Carbonate  Salt + Carbon dioxide gas + Water

17. Acids + Carbonates
How to test for carbon dioxide gas?
 Bubble the gas through limewater.
 Carbon dioxide forms a white precipitate with
limewater.

18. Acids + Carbonates
How to test for carbon dioxide gas?
 Bubble the gas through limewater.
 Carbon dioxide forms a white precipitate with
limewater.
Limewater
Bubble carbon
dioxide gas White
precipitate
formed

19. Acids + Alkalis
Acids react with alkalis to form a salt and water only.
The reaction between acids and alkalis is called
neutralisation.
3
Acid + Alkali  Salt + Water

20. Acids + Alkalis
Examples:
hydrochloric
acid
sodium
hydroxide
sodium
chloride
Water+  +
sulfuric acid
potassium
hydroxide
potassium
sulfate
Water+  +