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.