4.3.2. Oxidation

You have learnt about oxidation reactions in the first Chapter. Carbon compounds can be easily oxidised on combustion. In addition to this complete oxidation, we have reactions in which alcohols are converted to carboxylic acids.

In chemistry, oxidation refers to the process where a substance loses electrons or gains oxygen. In this context, carbon compounds, when burned (combustion), undergo oxidation. For instance, when ethanol, which is a type of alcohol, is completely oxidised, it gets converted to acetic acid (a carboxylic acid). This shows that carbon compounds are versatile and can undergo transformations during reactions.

Think of oxidation like cooking food. When you cook or burn something, it changes its form completely, just like how vinegar (acetic acid) is produced from ethanol when it is oxidised. Just like how charred food indicates it has been overcooked, the products produced after oxidation give clues about the process that took place.

We see that some substances are capable of adding oxygen to others. These substances are known as oxidising agents. Alkaline potassium permanganate or acidified potassium dichromate are oxidising agents used to oxidise alcohols to acids, that is, adding oxygen to the starting material.

Oxidising agents are substances that can accept electrons from other substances, thereby enabling oxidation reactions. For example, alkaline potassium permanganate and acidified potassium dichromate can add oxygen to alcohols, converting them into acids. This is important in many chemical reactions, especially in organic chemistry, where the conversion of compounds to others with different properties is often required.

Imagine oxidising agents as sparks in a fire. Just as a spark can ignite a wood log and trigger a big fire, oxidising agents kickstart chemical reactions that change substances from one form to another. For instance, adding a few drops of an oxidising agent to ethanol can lead to the production of acetic acid, much like how a small spark can lead to a large flame.

Take about 3 mL of ethanol in a test tube and warm it gently in a water bath. Add a 5% solution of alkaline potassium permanganate drop by drop to this solution. Does the colour of potassium permanganate persist when it is added initially? Why does the colour of potassium permanganate not disappear when excess is added?

In this experiment, the aim is to observe how potassium permanganate behaves when added to ethanol. When potassium permanganate is first added, it has a deep purple color, which disappears as it reacts with the ethanol. If the reaction goes to completion and there is no ethanol left, adding excess potassium permanganate doesn't change the solution further, which causes the color to persist. This indicates whether all the ethanol has reacted or if there is still some left.

Think of this experiment like adding food dye to a glass of water. As long as there is clear water, the dye will spread throughout. But if you keep adding dye after the water is fully colored, the water remains dyed and you won't see any change. Similarly, ethanol initially consumes the potassium permanganate, but if it's all used up, you'll see the color remain when excess dye (oxidising agent) is added.

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