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Discussion

Acetic acid is a weak monoprotic acid. It will react with sodium hydroxide, a strong base, in a one-to-one ratio:

HC₂H₃O₂(aq) + NaOH(aq) → NaC₂H₃O₂(aq) + H₂O(l)

If the solutions are of the same concentration, one would expect to use the same volume of sodium hydroxide solution to titrate the initial sample of acetic acid.

The first diagram is an unlabeled diagram of the initial and final titration conditions. A second diagram includes the concentrations of the acid and base. A diagram with the identity of the acid and base is shown next.

Narration

In this simple titration, one graduated cylinder contains 100 mL of sodium hydroxide. The other cylinder contains 40 mL of acetic acid, a monoprotic weak acid. The 40-mL sample of acetic acid is poured into a beaker and a small quantity of indicator is added. The molar concentrations of the two solutions are approximately equal. The solution is stirred as sodium hydroxide is carefully poured from the graduated cylinder into the beaker. As the sodium hydroxide is added, the indicator color begins to change to pink. When a permanent pink color develops, the titration is stopped. The level of sodium hydroxide in the graduated cylinder shows that about 42 mL of sodium hydroxide were used to titrate the 40-mL sample of acetic acid.