Indicators

to observe the equivalence point of a titration,
mostly is used an indicator color change
acid base titration: an acid base indicator
redoxtitration: a redox indicator


An indicator mostly is....:
a weak organic acid
a weak organic reductor
HIn H+ + In-
RedIn n e- + OxIn
HIn different color than In-
RedIn different color than OxIn
the color of HIn or In-
the color of RedIn or OxIn
only can be seen when the equilibrium is sufficiently at the right or the left side.
the color of an indicator depends on the environment:
In acid environment (or in a reducing environment)
the above equilibria are on the left side;
the color of HIn (or RedIn dominates.
It can be different per indicator.




Data about more indicators can be found in table VIII opvragen.

In acid-base titrations the pH of the final solution is not necessarily 7; the end pH depends on the properties of the products.
Those products can contain weak acids or weak basis.

Next general rules can be applied:

titration of a strong acid with a strong base: pH = 7
titration of a strong acid with a weak base: pH < 7
titration of a weak acid with a strong base: pH > 7


The right choice of indicator depends on the properties of the products and of the color change zone of the indicator (see table VIII)
You must match the indicator with the kind of titration.

If you want to execute an acid base titration without an indicator, than you could use a pH-meter, and continuously read on that meter the pH-change: in the equivalence point the pH-change is maximal; a sudden pH jump occurs.
You could make a graphic, with a plotter, of the course of the pH (see below).

Every time after adding, for example 0.5 ml, you read the value of the pH or the potential on a meter, and you notate that value; you can draw a graph, a titration curve, on graphic paper (or the plotter does it automatically); this way you can determine the right equivalence point.

In case of redoxtitrations you do not use a pH meter, but a voltmeter.