Brønsted–Lowry Acids and Bases

The Brønsted-Lowry theory defines an acid as a proton (H+) donor, and a base as a proton (H+) acceptor.
Water can play the role of an acid or a base, making it an amphoteric substance. When water acts as an acid, it donates a proton to a base, and becomes a hydroxide ion (OH -). When water acts as a base, it accepts a proton from an acid and becomes a hydronium ion (H3O+).
In an aqueous solution, the balance between water molecules and hydronium and hydroxide ions is known as the autoionisation of water. The equilibrium constant for this reaction is represented as Kw, also known as the ionic product of water.
An important aspect of the Brønsted-Lowry theory is the existence of conjugate acid-base pairs. When an acid donates a proton, it forms a base. This base is called the acid’s conjugate base because it is capable of accepting a proton to reform the original acid.
Similarly, when a base accepts a proton, it forms an acid. This acid is the base’s conjugate acid because it is capable of donating a proton to reform the original base.
The strength of an acid or a base can be determined by looking at its acid dissociation constant (Ka) or base dissociation constant (Kb). Acid or base strength is also indicated by the pH or pOH of a solution.
The Henderson-Hasselbalch equation can be used to calculate the pH of a buffer solution, which relies on the concept of acids and bases. The equation is pH = pKa + log([A-]/[HA]).
To solve problems involving Brønsted-Lowry acids and bases, it’s useful to write out the acid or base dissociation reactions, determine the conjugate acid or base, and use the Ka or Kb to calculate concentrations, pH or pOH. Practice with different types of problems will be helpful in mastering these concepts.
Acid-base titrations often involve Brønsted-Lowry acids and bases. These titrations can determine the concentration of an unknown acid or base, and they illustrate the fundamental properties of acids and bases in solution. The point at which the moles of acid equal the moles of base is called the equivalence point.
Indicators are used in acid-base titrations to visually signify when the equivalence point has been reached. Different indicators change colour at different pH values, so the choice of indicator depends on the pH at the equivalence point.