Thursday, April 18, 2013

Calculating pH of a weak base solution

Weak bases (B) such as ammonia partially ionize in water to give hydroxyl ions (OH-) and the corresponding conjugate acid (BH+). To calculate pH we need to know the concentration of the weak base (C) in Molar units and its Kb (base ionization constant) then use the following equations:

For example if we have 0.1 M ammonia ( Kb = 1.75×10-5 ) solution then if we use the above equation we get pH = 11.12.

Related posts:
Online pH calculator

Calculate pH of 0.1 M (molar) sodium acetate solution.


  1. This is obviously the quadratic equation. What happened to the 2a in the denominator?

    1. Yes. The above equation results from solution of a quadratic equation where a=1, b=Kb, and c=-Kb*C.

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