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Strong Acid, Strong base Titration

Calculate the pH of the solution when 0.1 M sodium hydroxide (NaOH) is titrated with a 25.0 mL hydrochloric acid (HCl) at the following stages of the titration.

a) 15.0 mL of the sodium hydroxide solution added

b) 25.0 mL of the sodium hydroxide solution added

c) 35.0 mL of the sodium hydroxide solution added

Solution Preview

In any multiple step titration problem it is important to calculate the equivalent volume, before attempting to solve the problem. Sodium hydroxide (NaOH) is a strong base and hydrochloric acid (HCl) a strong acid. The reaction is shown below:

NaOH (aq) + HCl (aq) => NaCl (aq) + H2O (l)

The balance equation shows a 1:1 ration between the acid and the base and can be represented by this simple formula;

MaVa = MbVb where Ma and Mb are molarity of base and acids respectively and Va and Vb are volumes of base and acid. The equivalent volume, i.e. the amount of base added to attend equilibrium is Ve = Vb.

Ve = Vb = MaVa/Mb ...

Solution Summary

A solution present strong acid, strong base titrations at three important stages. First being before equivalent point, where there is excess acid, then at equivilant point where there is equal amount of acid and bases and finally after equivalent point where there is excess base.