Model neutralisation of strong and weak acids and bases using a variety of media

Strong acid – strong base neutralization

  • A strong acid completely dissociates in aqueous solution. For example, hydrochloric acid, HCl, is a strong acid.

HCl(aq) → H+(aq) + Cl−(aq)

  • A strong base completely dissociates in aqueous solution. For example, sodium hydroxide, NaOH, is a strong base.

NaOH(aq) → Na+(aq) + OH−(aq)

  • Therefore, when a strong acid reacts with a strong base the neutralization reaction can be written as

H+ + OH− → H2O

 

Weak acid – strong base neutralization

  • Weak acids partially dissociate in aqueous solution.

HA(aq) + H2O ↔ H3O+(aq) + A−(aq)

  • When a strong base neutralizes a weak acid, due to the partial dissociation of the acid, excess amount of base remains in the solution and when the reaction reaches the endpoint, the pH is more than 7.

 

Weak base – strong acid neutralization

  • Analogous to weak acid – strong base neutralization, weak bases partially dissociate in aqueous solution and thus complete neutralization does not occur.

HA + B ↔ BH++ A−

  • The pH of the neutralized solution depends on the acid dissociation constant of the base, pKa, or, equivalently, on the base association constant, pKb.

 

Weak base – weak base neutralization

  • Both weak acids and bases have a slower rate of dissociation and thus they cannot be neutralized by one another.