Question

From our bottle of wine; 3x 100 mL sample replicates were produced and the pH adjusted to pH 7.9 by addition of 4.0 mL of NH4OH (0.5 M) with phosphate buffer. The solution was then coloured with 1.0 mL of 2% (w/v) dye solution and 1.0 mL of 8% (w/v) K3Fe(CN)6 solution. The resulting solutions were left to stand for 15 minutes for colour development. Question is : yielding identical products. If phenol compounds are oxidised… what reagent is reduced? Write a generalised equation for this reaction. What is the role of the Fe3+ complex?

Answer 1

The question describes the phenomenon and the experimental process like a story. But, the actual question is: If phenol compounds are oxidized, what chemical compound is acting as an oxidant? They also mentioned that the phenol compounds present in the wine are getting oxidised. We have to write a generalised equation for the oxidation process and the role of Fe3+ complex in oxidation. Now, it has become pretty simple:

The ferricyanide complex contain Fe in +III oxidation state. Oidation, by definition, involves the loss of electrons. An Oxidant undergoes reduction by accepting electrons. Hence, Phenolic compounds looses electrons and the Fe(III) atom accepts electrons and becomes Fe(II). Hence, the answer. The general formula is as follows: