Acids are defined as a proton donor

A Base is defined as a proton acceptor

Strong Acid
An acid which dissociates (ionise) fully when aqueous

Weak Acid
An acid which dissociates partially when aqueous in water

Whilst concentration is the number of atoms within a given volume, acids can be referred to as strong or weak. This provides an indication of the number of protons that dissociate when aqueous in water. For example hydrochloric acid or sulphuric acid are strong acids with a high concentration of protons when aqueous in water.

HCl H+ + Cl-

H2SO4 2H+ + SO42-

Ethanoic acid is an example of a weak acid. For every 1000 ethanoic acid atoms only 4 protons dissociate.


Therefore HCl reacts faster than CH3COOH, even if the acids have the same concentration.


Ionic equations

For Module 3 you will only come across three ionic equations:

HCl + NaOH H2O + NaCl
H+ + OH- H2O

Neutralisation with a carbonate:
CaCO3 + 2HCl CO2 + H2O + CaCl2
H+ + CO32- H2O

Reaction between a metal and acid:
Mg + 2HCl MgCl2 + H2
Mg + 2H+ Mg2+ + H2