What is used to test for reducing and oxidising agents?

Answer 1

When some substances are oxidised or reduced, there is a colour change.

Testing for a reducing agent:

An oxidising agent is a substance that causes another substance to be oxidised & is itself reduced. Acidified potassium manganate (VII) is an example of one. While it oxidises other substances, the manganate ion is reduced (because the oxidation state decreases showing that reduction is occuring) :

MnO4- --> Mn2+

oxdations state:

+VII

+2

colour:

Pink

Colourless

So, to see if an unknown substance is a reducing agent, add acidifies potassium manganate (VII) to see if the pink colour fades. If it does, you know the unknown substance was a reducing agent, because it caused reduction.

Testing for an oxidising agent:

A reducing agent is a substance which causes reduction, but is oxidised itself. Potassium iodide is a powerful reducing agent. While it reduces other substances, the iodide ion is oxidised (because the oxidising state increases) resulting in a colour change:

2I- -->

I2

Oxidising state:

-1

0 (the oxidising state of a diatomic molecule is 0)

Colour:

Colourless

Red-brown

So, to see if an unknown substance is an oxidising agent, add potassium iodide to see if a red-brown colour appears. If it does, you know your unknown substance is an oxidising agent because it caused a reduction

Answer 2

One common test for reducing agents is the Benedict's test, which detects the presence of reducing sugars by forming a colored precipitate. The iodine test is often used to test for starch, which is not strictly a reducing agent, but it can give an indication of the presence of polysaccharides that may contain reducing sugar units. A common test for oxidising agents is the potassium permanganate test, where the purple color of the permanganate solution fades as it is reduced by the oxidising agent.