Question

Why is potassium dichromate not a self indicator?

Answer 1

Potassium dichromate:

1. Potassium dichromate is a powerful oxidising agent, but not as powerful as potassium permanganate, and it can only be used in acidic environments.
2. As an indication, it emits a yellowish colour, but not as a self-indicator.

Reasons for potassium dichromate not a self indicator:

1. Because of the colour, the chromate ions $\left(C{r}^{+3}\right.)$ give off at the end of the reaction, potassium dichromate cannot be used as a self-indicator.
2. The dichromate solutions are usually orange, but they cannot be used as self-indicators. This occurs when dichromate ions are reduced to simply chromium ions, resulting in green colour.
3. This does not assist in the optical recognition of endpoints by dichromate colour, but rather hinders it.
4. Even if detection is possible, it is impossible to be precise because we cannot know when the colour changes. As a result, using it as a self-indicator will not suffice; an indicator must be added in order for it to be ideal.
5. Potassium permanganate, on the other hand, can be employed as a self-indicator.
6. This is not the case with potassium permanganate, which can be hampered by colour variation. It only hinders potassium dichromate due to the reduction of chromium ions, which provides a green colour.
7. Normally, the solution with potassium dichromate as an indicator will be yellow, but the colour change visualisation is hampered due to chromate ions.