Weak Acid

 

                

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Titration of Weak Acids with Strong Bases or Weak Bases with Strong Acids

The weak acid-strong base or the weak base-strong acid titration can be classified into four distinct regions.   These are described below for the stepwise addition of strong base to a weak acid solution.

  1. Solution of only weak acid (solution of H3O+)
  2. Excess moles of weak acid + limiting moles of strong base (buffer solution)
  3. Equivalence Point with equal moles of weak acid + strong base (solution of conjugate weak base from the weak acid)
  4. Excess moles of strong base + limiting moles of weak acid (solution of OH-)

*The same principles are applied to the regions of a weak base titrated with strong acid.

The following example illustrates the calculations involved in the titration of a weak acid with a strong base.  The four regions outlined above are presented stepwise as strong base is titrated into the weak acid solution.  Be sure to understand the techniques used to solve for the concentrations of species involved in each step along the way.  Click on a "titrant added" value to see the calculation pertaining to that point in the titration.

SAMPLE:  receiving flask containing 50.00 mL of a 0.100 M HF(aq) solution (weak acid).

TITRANT:  stepwise addition of a 0.200 M KOH(aq) solution (strong base) from a buret using the following volumes:

titrant added region classification

pH of resulting solution
0.00 mL 1 2.10
10.00 mL 2 2.99
24.90 mL 2 5.5
25.00 mL 3 8.00
25.10 mL 4 10.42
30.00 ml 4 12.10
40.00 ml 4 12.50

*Special thanks to Dr. Fred Wood at U.C. Davis for the foundations of this tutorial!