Edexcel IAL Chemistry A2 14.9 Weak acid pH from Ka or pKa
Edexcel IAL Chemistry A2 14.9 Weak acid pH from Ka or pKa
Start by converting pKa when needed, use [H+]^2 = Ka[HA] only when the assumptions are justified and finish by checking that the pH remains acidic.
How this is tested
- Calculate [H+] and pH from Ka and the initial weak-acid concentration.
- Convert pKa to Ka before rearranging the weak-acid expression for pH or required mass.
- State assumptions such as negligible water ionisation and [HA]initial approximately [HA]equilibrium.