We can occupational out the concentrations of all the species at equilibrium by means of the ICE table.

You are watching: How to calculate ph of weak base

calculate pH of weak base ICE table

We deserve to then substitute these worths into the base dissociation constant (Kb) expression.

In order to deal with for x, we must impose an approximation to stop resolving quadratic equation.

We will certainly assume that the concentration of weak base at equilibrium is equal to its original concentration.

We have the right to then rearvariety the equation to determine x, which is the concentration of OH-.

calculate pH of weak base substitute right into Kb with approximation

Because we are dealing largely with monoprotic species in Ionic Equilibria, the ICE table and also approximation is constantly valid.

Because of this we deserve to use the following formula to conveniently recognize OH- concentration when Kb and weak base concentration are provided.

calculate pH of weak base formula

For this exercise Kb of ammonia is not given.

But we have the right to gain this conveniently from the Ka of its conjugate acid NH4+ and Kw, the ionic product of water.

calculate pH of weak base Ka Kb equals Kw

Please note Ka.Kb = Kw just applies to conjugate acid-base pairs.

We can currently usage the formula method to find OH- concentration.

calculate pH of weak base calculate hydroxide concentration

Finally we deserve to determine pOH and also pH of this weak base.

calculate pH of weak base calculate pOH and pH

Topic: Ionic Equilibria, Physical Chemistry, A Level Chemistry, Singapore

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