Water purification techniques have long sought the attention of researchers. It is actually one of the primary reasons which drive scientific advancements.
So, naturally, it comes as no surprise that humankind has come up with different solutions to overcome such adversity. Would you like to know what was one of the earliest methods to purify water?
The answer is potassium permanganate (KMnO4).
Not only is the compound used to purify water but has tons of uses. Where could you have seen this compound?
When you entered your chemistry lab, you may have seen beakers with a dark purple liquid solution. It looks so beautiful, teachers ask you to do titrations using this purple solution. This compound has long fascinated researchers in regards to its versatility and its potential applications. We will study more about this coloured compound and see how useful is this in chemistry.
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The first indications of KMnO4 were discovered when a German-Dutch chemist named Johann Rudolf Glauber began his investigations by mixing two compounds: pyrolusite (MnO2), a manganese dioxide and potassium carbonate mineral. He turned the combination into a green solution by dissolving it in water. This was manganese potassium. The colour of the solution gradually changed from blue to violet and then crimson. This experiment was the first time KMnO4 was produced.
KMnO4 is an inorganic ionic compound that consists of K+ ion and MnO4- ion. The manganese atom is attached to four oxygen atoms by three double bonds and one single bond in the permanganate anionMnO4-. Manganese in this salt has an oxidation state of + 7. Hybridisation of MnO4- ion comes out to be d3s (orbitals utilised are 3dxy, 3dyz, 3dzx and 4s).
Structure of KMnO4 in the above structure, the bonds between (Mn) and the oxygen atoms have a partial double bond character, and this is because of resonance present here.
|Reduction half-reaction||Electrode potential values; E°(V)|
The following are some of the most notable reactions of KMnO4:
1. In an acidic environment: Potassium iodide is broken down to give iodine.
2. In slightly alkaline or neutral solutions:
Effects on Health:
Q1. What is the coefficient of sulphate ions when sulphite reacts with permanganate ions?
Solution: Sulphurous acid or sulphite is converted to sulphate or sulphuric acid with a reaction with permanganate ion. Below is the required balanced reaction:
Q2. Example of redox titration is
A. Titration of potassium permanganate against oxalic acid
B. Titration of silver nitrate against ammonium thiocyanate
C. Titration of acetic acid against sodium hydroxide
D. Titration of calcein against EDTA
Solution: A general example of redox titration is demonstrated by the titration of potassium permanganate (KMnO4) against oxalic acid (C2H2O4).
Q3. Represent a reaction in the acidic medium in which KMnO4 acts as oxidising agent.
Solution: The following equation can be used to represent the oxidising activity of KMnO4 in an acidic medium:
Q4. Potassium permanganate is used as a self indicator because of __________
A. It behaves as a strong oxidising agent
B. It breaks down into ions easily
C. It gets disproportionated in acidic medium
D. It undergoes a chemical change resulting in colour difference.
Solution: Potassium permanganate has a rich violet colour that is extremely visible to the human eye, and when it is titrated, there is a noticeable loss of colour.
Question1. Potassium permanganate acts as a preservative for fruits. How?
Answer. Because the permanganate inhibits ripening by oxidising ethylene, the fruit can last up to four weeks without refrigeration and thus it acts as a preservative.
Question2. Is KMnO4 combustible in nature?
Answer. No, KMnO4 is not combustible in nature but it enhances the combustion of other substances. It gives off irritating fumes in a fire.
Question3. Is potassium permanganate safe to eat?
Answer. No, it is not safe to consume potassium permanganate. The upper gastrointestinal system may be damaged if potassium permanganate is consumed. It can also produce systemic side effects including adult respiratory distress syndrome, coagulopathy, hepatic-renal failure, pancreatitis, and even death in extreme situations.
Question4. How do one can get out from KMnO4 stains present on nails or clothes?
Answer. To get KMnO4 stains removed, cut a lemon, and treat the affected region of the skin, clothes or nails with the lemon peel. It will work like magic and completely remove the discolouration.
|f block elements||Transition elements|
|Hydrogen||Important compounds of copper|