Strength of
Acid and Alkalis
The strengths
of acids and alkalis are determined by the extent of their ionization in water.
Strong Acids
1.A strong acid is an acid that is
completely ionized in water to form high concentration of H+ ions.
2.Examples of strong acids are
hydrochloric, sulphuric and nitric acids.
HNO3 (l) + aq ® H+ (aq) + NO3- (aq)
HCl (g) + aq ® H+ (aq) + Cl- (aq)
H2SO4 + aq ® H+ (aq) + SO42- (aq)
Strong Alkalis
1.A strong alkali is an alkali that
is completely ionized in water to form high concentration of OH- ions.
2.Examples of strong alkalis are
sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.
NaOH (s) + aq ® Na+ (aq) + OH- (aq)
Ca(OH)2 (s) + aq ® Ca2+ (aq) + 2OH- (aq)
Weak Acids
1.A weak acid is an acid that is partially ionized in water.
2.Examples of weak acids are ethanoic acid, carbonic
acid, methanoic acid and other organic acids.
CH3COOH (l) + aq « CH3COO- + H+
Weak Alkalis
1. A weak alkali is an alkali that is partially ionized in water.
NH3 (aq) + H2O (l) « NH4+ (aq) + OH- (aq)
HCO3- + H2O (l) « CO32- (aq) + OH- (aq)
2. Only a relatively low concentration of free hydroxide ions are
formed in both ammonia and sodium hydrogen solutions.
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