Titration Curves

Strong Acid with Strong Base

You should already be familiar with the titration curve generated when a strong acid is titrated with a strong base. The net ionic equation for the reaction is H3O+(aq) + OH-(aq) ----> 2H2O(l). The titration curve and a summary picture of the species in solution are given below.

S shaped pH curve resulting from titrating strong acid with strong base Initially pH is low, rises rapidly a the equivalence point, and ends high.

At the stoichiometric or equivalence point (S on the curve), stoichiometrically equivalent amounts of acid and base have reacted and the reaction is complete. Note that at the stoichiometric point, the pH is 7 because water is the only product.

 

Weak Acid with Strong Base

The net ionic reaction for the titration is shown below.

HA(aq) + OH-(aq) ---> A-(aq) + H2O(l)

The composition of the solution at important points in the titration is shown in the static view below. Since M+ is a spectator ion it is not shown.

weak acid titrated with strong base: pH starts low, rises as it enters the buffer zone, rises quickly at the stoichiometric point and ends high.

Note that until we reach the stoichiometric point, OH-(aq) is in deficit and is completely consumed. At the half-neutralization point, the major species are HA(aq) and A-(aq) and at the stoichiometric point, the major species is A-(aq). Because A- is a base, the pH is greater than 7 at the stoichiometric point. Click on animation to see a dynamic view of the titration. When you are finished, use the "back" button on your browser to return to this page.

 

Weak Base with Strong Acid

The titration curve for the reaction of a weak base with a strong acid is shown below.

Titration of weak base with strong acid shows an inverted S curve.  Starts high, drops sharly, ends low.

The net ionic equation for this reaction is

B(aq) + H3O+(aq) ----> BH+(aq) + H2O(l)

At the stoichiometric point, S on the curve, the major species is BH+(aq) and therefore the solution is acidic. What is the net ionic equation which shows that the solution is acidic? At the half-neutralization point in the titration, what are the major species in the solution and what is the pH equal to?

Answers