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Test for Oxidizing and Reducing Agents

 

To test for oxidizing and reducing agents in the laboratory, substances, which will give colour change when they either get oxidized or reduced, are used.

To Test for Oxidizing Agents

 (a). Iron(II) chloride, FeCl2 - the solution of this substance (Fe2+) is green in color. When reacted with a substance suspected to be an oxidizing agent, and its color changes to reddish brown, then the substance is confirmed to be an oxidizing agent. The Fe2+ ion is oxidized to Fe3+ ion.

(b). When a strip of moist starch – iodide paper is dipped into a substance suspected to be an oxidizing agent, and a blue black color appears, then the substance is confirmed to be an oxidizing agent.

The oxidizing agent oxidizes the iodide to free iodine. The solution of the free iodine then reacts with the starch to give the blue black color (notice that it is only the solution of the free iodine which gives the blue black color with the starch).

(c). When hydrogen sulphide (H2S) is reacted with a substance, and some yellow deposits (sulphur) are settled on the bottom of the container, then the substance is an oxidizing agent – H2S is oxidized to sulphur.

To Test for Reducing Agents

(a). Reacting the suspected reducing agent with potassium tetraoxomanganate(VII) solution, KMnO4 (purple color), and the color is observed to become colorless (Mn2+), the substance is confirmed to be a reducing agent. KMnO4 is reduced to Mn2+.

(b). Also, a solution of potassium heptaoxodichromate(VI), K2Cr2O7 (orange in color) would become greenish (Cr3+) when reacted with a reducing agent.   

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