Page 9 - Analytical Chemistry 1

A strong acid is an acid that ionizes completely in water, it is a

strong electrolyte, e.g. HCl (aq) and HNO3 (aq). A weak acid is an acid

that only partly ionizes in water; it is a weak electrolyte, e.g HCN (aq)

and HF (aq). These molecules react with H2O to produce a small % of

ions in solution leaving the majority of the acid molecules unreacted.

* HCl (aq) + H2O (l) ⎯→ H3O+ (aq) + Cl- (aq)

HNO3 (aq) + H2O (l) ⎯→ H3O+ (aq) + NO3- (aq)

* HCN (aq) H2O (l) H3O+ (aq) + CN- (aq)
HF (aq) + H2O (l) H3O+ (aq) + F- (aq)

A strong base is a base that is present in aqueous solution entirely
as ions, one of which is OH-, it is a strong electrolyte, e.g. NaOH or
generally the hydroxides of groups IA & IIA elements (except Be (OH)2).
A weak base is a base that is only partly ionized in H2O; it is a weak
electrolyte, e.g. ammonia.

H2O
NaOH (s) ⎯→ Na+ (aq) + OH- (aq)

NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

When you write an ionic equation, you represent strong acids and

bases by the ions they form and weak acids and bases by the formulas of

the compounds. In addition, the reaction for weak electrolytes is

reversible ( )

3. Chemical equilibrium for acid-base reactions:

Chemical equilibrium:

• Most chemical reactions are reversible i.e. products of a given reaction

interact to some extent to reform the initial substances.

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