In a titration a fast reaction is carried out in solution, one reactant being added dropwise from a burette to the other in a flask. Acid-base reactions can be carried out by titration provided either the acid or the base is strong.
A titration curve is a plot of pH against volume of titrant added from the burette. Titration curves show how the pH of a solution changes as the acid or base solute in the flask is consumed by reaction with a titrant added from a burette.
Titration curves for four different pairs of acids and bases are shown below.
The curves show that
A titration curve is a plot of pH against volume of titrant added from the burette. Titration curves show how the pH of a solution changes as the acid or base solute in the flask is consumed by reaction with a titrant added from a burette.
Titration curves for four different pairs of acids and bases are shown below.
 |
| HCl (in flask) with NaOH (in burette) |
 |
| NaOH (in flask) with HCl (in burette) |
 |
| CH3CO2H (in flask) with NaOH (in burette) |
 |
| NH3 (in flask) with HCl (in burette) |
The curves show that
- the initial pH depends on the substance in the flask. for a strong acid, pH is lower (1-2) than for a weak acid
for a strong base pH is higher (12-13) than for a weak base - the direction of change in pH depends the substance in the burette pH increases if base is added from the burette
pH decreases if acid is added from the burette - there is a steep change in pH at the equivalence volume. Equivalence is when exactly enough of the titrant (from the burette) has been added to consume the substance in the flask.
The equivalence volume depends on the amount of substance in the flask and on the concentration of the titrant. - the final pH is that of diluted titrant (substance in the burette) if strong base is the titrant (pH is 12 - 13)
If strong acid is the titrant (pH is 1 - 2)