Potassium permanganate (KMnO4) is used for purifying drinking water primarily because it acts as which type of agent?

Introduction / Context:
Potassium permanganate is a deep purple compound widely used in chemistry laboratories and in some water treatment practices. When added in small quantities to drinking water, it helps in disinfection and removal of certain impurities. Understanding why it is effective requires basic knowledge of redox reactions and the role of oxidising agents. This question asks you to identify the main property of potassium permanganate that makes it useful for water purification.

Given Data / Assumptions:

• The compound is potassium permanganate, with formula KMnO4.
• It is used in small doses to help purify drinking water.
• Options include reducing agent, oxidising agent, sterilising agent, impurity dissolver, and pH buffer.
• We assume standard school level explanation of its role in oxidising organic matter and micro organisms.

Concept / Approach:
Potassium permanganate is a powerful oxidising agent in both acidic and neutral solutions. As an oxidising agent, it can accept electrons from other substances, thereby oxidising organic matter, iron, manganese, and micro organisms present in water. This oxidation can inactivate pathogens and convert certain dissolved pollutants into forms that can be removed more easily. Its effectiveness in purifying water is therefore mainly due to its oxidising nature rather than simply acting as a physical steriliser or a solvent for impurities.

Step-by-Step Solution:
Step 1: Recall that an oxidising agent is a substance that gains electrons in a chemical reaction and causes another substance to lose electrons. Step 2: Potassium permanganate contains manganese in a high oxidation state and readily accepts electrons, being reduced to lower oxidation states. Step 3: When added to water, KMnO4 oxidises various dissolved organic impurities and some micro organisms, contributing to disinfection. Step 4: This oxidative action helps reduce odour and colour and can assist in precipitation of certain metals such as iron and manganese. Step 5: It is not primarily a reducing agent and does not simply dissolve impurities; instead, it chemically transforms them. Step 6: Therefore, the reason potassium permanganate is used for purifying drinking water is that it is a strong oxidising agent.

Verification / Alternative check:
Water treatment manuals and chemistry textbooks describe potassium permanganate as a powerful oxidant used for pre oxidation, taste and odour control, and control of iron and manganese in water supplies. In redox titrations, KMnO4 is used as a standard oxidising agent, illustrating its strong oxidising ability. The purple colour disappears as it is reduced, which can also serve as an indicator that it has reacted with impurities. These repeated uses in redox contexts confirm that its key property is being an oxidising agent.

Why Other Options Are Wrong:
A strong reducing agent: The opposite of reality; potassium permanganate is not known as a reducing agent and does not donate electrons in these reactions.
A simple sterilising agent without chemical reaction: Disinfection here occurs through oxidation reactions, not by mere physical presence.
A substance that dissolves solid impurities: KMnO4 does not act like a detergent; it changes the chemical nature of impurities through oxidation.
A pH neutral buffer: Although the solution may have some effect on pH, potassium permanganate is not primarily used as a buffer for maintaining pH.

Common Pitfalls:
Students sometimes confuse oxidising agents with general disinfectants and may select sterilising agent, ignoring that the sterilisation is accomplished specifically by oxidation. Another error is to think that any compound used in water treatment must be a reducing agent or simply a dissolving agent. To avoid such confusion, remember that potassium permanganate is a classic textbook example of a strong oxidising agent used in both analytical chemistry and water purification.

Final Answer:
Potassium permanganate purifies drinking water primarily because it acts as a strong oxidising agent.