In this post, let’s talk about acids for O Level Chemistry.
- What are acids
- Properties of acids
- Common acids
- Weak vs strong acids
- Acid reactions
- More about acids, bases and salts
What are acids – O Level Chemistry definition
In O Level Chemistry, students learn that an acid is a substance that dissociates to give hydrogen ions (H+) in water.
In the example below, hydrogen chloride (HCl) dissolves and dissociates in water to give hydrogen ion. Hence, hydrochloric acid is an acid.
HCl (aq) –> H+(aq) + Cl–(aq)
This is an Arrhenius Acid (do note that there are many definitions of acids, and the one that we learn in O level chemistry is the Arrhenius one).
Properties of acids
Some common properties we are familiar with include acids have a sour taste, turn blue litmus paper red, and are corrosive.
Common Acids in O Level Chemistry
Here are the common acids in O Level Chemistry:
| Name | Formula | Dissociation Equation |
| hydrochloric acid | HCl | HCl (aq) –> H+(aq) + Cl–(aq) |
| nitric acid | HNO3 | HNO3 (aq) –> H+(aq) +NO3 –(aq) |
| sulfuric acid | H2SO4 | H2SO4 (aq) –> 2H+(aq) + SO42-(aq) |
| ethanoic acid | CH3COOH | CH3COOH (aq) ⇌ H+(aq) + CH3COO–(aq) |
Notice that all the acids ionizes or dissociates in water to give hydrogen ions in water? Hence they are acids.
Weak vs Strong Acids
A weak acid is one that dissociates partially in water. E.g. most organic acids such as ethanoic acid. The reversible arrow sign (⇌) indicates partial dissociation.
CH3COOH (aq) ⇌ H+(aq) + CH3COO–(aq)
A strong acid is one that dissociates completely in water e.g. hydrochloric acid, sulfuric acid, nitric acid. The arrow (–>) indicates complete dissociation.
HCl (aq) –> H+(aq) + Cl–(aq)
Acid reactions
Here are the acid reactions to know for O Level Chemistry:
1. Acids react with reactive metals (i.e. metals above hydrogen in the reactivity series) to give salt and hydrogen
word equation: acid + metal –> salt + hydrogen
2. Acids react with bases to give salt and water
word equation: acid + base –> salt + water
3. Acids react with carbonates to give salt, carbon dioxide and water
word equation: acid + carbonate –> salt + carbon dioxide + water