An acid-base indicator is a weak acid that changes colour in response to changes in pH. It is used to determine the end point of a titration.

A pH titration curve is a graphical representation of how the pH of a solution changes as an acid or base is added during a titration.

The equivalence point of a titration is the point at which the moles of acid and base are stoichiometrically equivalent, resulting in complete neutralisation.

The shape of the pH titration curve stays the same but it is flipped vertically as shown in the graphs above.

The indicator should give a sudden and distinct colour change within a suitable pH range close to the equivalence point, i.e. the pH range of the indicator should coincide with the vertical section of the titration curve.

Upon addition of a basic solution containing OH^- ions:

1. OH^- ions from the base react with H⁺ ions in the indicator.
2. The position of equilibrum shifts to the right.
3. The colour of the solution changes to the colour of A^-.

At the end point of a titration, the solution contains equal concentrations of HA and A^- so the colour of the indicator will be in between the colours of HA and A^-.

No indicator is suitable because there is no sharp change in pH at the equivalence point.

A pH meter is calibrated by adjusting the meter's readings to match known pH values of standard solutions.

Upon addition of an acidic solution containing H⁺ ions:

1. H⁺ ions from the acid react with A- ions from the indicator.
2. The position of equilibrum shifts to the left.
3. The colour of the solution changes to the colour of HA.

The endpoint is the point at which the reaction between the acid and base is complete.