ABC -Strong Acid and Base Titrations (Lesson)

Strong Acid and Base Titrations

Titrations

A titration is a type of analysis where one substance is systematically added to a second substance of unknown concentration to determine the concentration of the unknown. While a titration can be performed with a wide variety of different types of chemical reactions, a very common type of titration is an acid/base titration. Even though a titration is typically performed to simply determine the concentration of an unknown, it is possible to track the changes in the pH of the solution at various points during the titration.  

In this lesson, only titrations between strong acids and strong bases will be considered. The calculations for this scenario are significantly different than those for a weak acid/strong base which will be dealt with in the next lesson. Shown below is a plot of pH vs. volume of NaOH added for a titration between the strong acid HCl and the strong base NaOH. The chemical reaction describing this process is written above the plot. Notice that this is not an equilibrium situation, as has been discussed thus far, and the reaction proceeds to completion. 

HCl (aq) + NaOH (aq)  ⟶  NaCl (aq) + H2O (l)

TitrationOfStrongAcid

In a future lesson, this plot will be compared to that of a weak acid/strong base titration, but there are a few common features that can be pointed out:

  1. Notice that the plot begins at a low pH due to the presence of acid only at the initial point (before any base has been added).
  2. There is an abrupt increase in pH as the reaction reaches the equivalence point. The equivalence point will be further explained in the videos posted below, but it is important to note that this is the point where the moles of strong base that have been added are equal to the moles of strong acid that were originally present.
  3. For a strong acid/strong base titration ONLY, the pH at the equivalence point is equal to 7.00

The videos below illustrate how to perform pH calculations at several important points along the titration curve. The overall process is the same at each point; however, there are several key differences that are pointed out in each video.

Titration of a Strong Acid with a Strong Base, Video One

Titration of a Strong Acid with a Strong Base, Video Two

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