Acid-Base Reactions

This lecture series will cover:

Chemical equilibrium, the equilibrium constant, Ka, Kb and pH scales
Bronsted-Lowry, weak and strong acids and bases, pH calculations

An acid is a proton donor and a base is a proton acceptor.

Conjugated acid base pairs are two compounds which are converted by the loss of a proton from the acid to form the base, for example NH4+ and NH3.

Le Chatellier’s principle:

When a system is subject to change, the system alters to lessen the effect of the change
Factors which can be changes:
- Concentration - Increasing concentration of reactants will favor the reaction that produces the products and increase yield. Decreasing the concentration of products will favor the formation of the reactants
- Pressure - Increasing pressure favours the side with the fewer moles and increase the yield of products on this side of the reaction
- Temperature - Increasing temperature favours the endothermic reaction and increases the yield of endothermic products

The ionic product of water is referred to as Kw. This is the equilibrium constant for the dissociation of water (see reaction). This changes with temperature.

A strong acid completely dissociates to ions, whereas a weak acid only partially dissociates.

Titration curves can be used to show how the pH of a solution changes during an acid-base reaction. When the two compounds react, a neutralisation point is reached when the pH changes very quickly (shown as a vertical section when this is plotted on a graph). This can be visualised through an indicator which changes at the relevant pH range.

Buffers are solutions which maintain a constant pH on addition of small amounts of an acid or base. They are used in nature to keep systems regulated, as processes often require a specific pH to work efficiently.