Behaviour of Strong and Weak Acids and Alkalis and Buffer Solutions

Behaviour of Strong and Weak Acids and Alkalis and Buffer Solutions

Strong Acids and Alkalis

  • Strong acids and alkalis are substances that completely dissociate in aqueous solutions.
  • Examples of strong acids include hydrochloric acid (HCl), nitric acid (HNO3), and sulphuric acid (H2SO4).
  • Strong alkalis, like sodium hydroxide (NaOH), potassium hydroxide (KOH), and barium hydroxide (Ba(OH)2), produce hydroxide ions (OH-) when dissolved in water.
  • This full ionisation contributes to their high conductivity and reactivity.
  • However, their pH values need to be calculated with care, considering their full ionisation.

Weak Acids and Alkalis

  • Weak acids and alkalis, unlike their strong counterparts, only partially ionise in solution.
  • This partial ionisation leads to a dynamic equilibrium between the ionised and un-ionised forms.
  • Examples of weak acids include ethanoic acid (CH3COOH) and carbonic acid (H2CO3).
  • Examples of weak alkalis are ammonia (NH3) and ammonium hydroxide (NH4OH).
  • The partial ionisation of weak acids and alkalis results in them being less conductive and reactive compared to strong acids and alkalis.
  • pH calculations for weak acids require knowledge of the acid dissociation constant (Ka), or for weak alkalis, the base dissociation constant (Kb).

Buffer Solutions

  • Buffer solutions are solutions that resist changes in pH, even when small amounts of an acid or an alkali are added.
  • These solutions consist of a mixture of a weak acid and its corresponding conjugate base, or a weak alkali and its corresponding conjugate acid.
  • The constant pH is maintained due to the equilibrium set up between the weak acid (or alkali) and its conjugate pair.
  • This equilibrium can accommodate for incoming H+ or OH- ions added to the solution, preventing significant changes in pH.
  • An understanding of the Henderson-Hasselbalch equation is vital for calculating the pH of buffer solutions.