IB Chemistry - Acids and Bases

IB Chemistry home > Syllabus 2016 > Acids and Bases > Calculations involving acids and bases

Syllabus ref: 18.2

In this section we will look at how to manipulate the necessary equations to calculate acidity, basicity and other quantities relating to the topic.

Nature of science:

Obtaining evidence for scientific theories - application of the equilibrium law allows strengths of acids and bases to be determined and related to their molecular structure.


Essential idea: The equilibrium law can be applied to acid-base reactions. Numerical problems can be simplified by making assumptions about the relative concentrations of the species involved. The use of logarithms is also significant here.

The expression for the dissociation constant of a weak acid (Ka) and a weak base (Kb).

For a conjugate acid base pair, Ka × Kb = Kw.

The relationship between Ka and pKa is (pKa = -log Ka), and between Kb and pKb is (pKb = -log Kb).

Applications and skills

Solution of problems involving [H+ (aq)], [OH-(aq)], pH, pOH, Ka, pKa, Kb and pKb.

Discussion of the relative strengths of acids and bases using values of Ka, pKa, Kb and pKb.

In Chapter 8.5