Potassium Permanganate: Uses, Grades and Safety

Potassium permanganate is a dark purple, almost black crystalline salt that dissolves in water to give a deep pink to purple colour. Many Indian households know it as lal dawa. It is a strong oxidising agent, which means it pulls electrons from other substances and changes them chemically.

• Formula: KMnO4
• CAS number: 7722-64-7
• Molar mass: 158.03 g/mol
• Solubility: about 76 g per litre of water at 25 °C
• Heating: decomposes at about 240 °C instead of melting

As it reacts, the purple colour fades and brown manganese dioxide forms. That brown stain on buckets and skin is the sign it has done its work.

Azlok stocks potassium permanganate in two grades.

Extrapure material has tighter limits on impurities, which matters when you need accurate results. For water treatment, technical grade does the job. Check today's price per kg before ordering.

Potassium permanganate falls under controlled-substance rules in India, so Azlok may limit the quantity you can buy per order or per month.

Water treatment

• Oxidising dissolved iron and manganese in well and borewell water so they can be filtered out
• Removing the rotten-egg smell caused by hydrogen sulphide
• Controlling taste and odour in municipal treatment plants

Laboratory

• Redox titrations (permanganometry), for example estimating iron or oxalate
• Testing for unsaturation and other teaching experiments

Industry

• Oxidant in organic chemical manufacture
• Treating industrial wastewater and in some metal surface treatment

Iron and manganese in water. The textbook doses are about 0.94 mg of potassium permanganate per mg of iron, 1.92 mg per mg of manganese, and around 6 mg per mg of hydrogen sulphide. Get a water test first so you know the levels. In practice:

1. Dissolve the crystals fully in a small amount of water first. Undissolved crystals stain tanks.
2. Add the solution to the water and mix. A faint pink colour that lasts a few minutes shows enough has been added.
3. Let the brown precipitate settle for a few hours, or pass the water through a sand or manganese greensand filter.
4. If the water stays pink, you have overdosed. Wait and let it fade before using the water.

Lab titrant (about 0.02 M, often called 0.1 N). Dissolve about 3.2 g in 1 litre of distilled water, heat or let it stand, filter through glass wool, and standardise against sodium oxalate or oxalic acid. Store in an amber bottle.

• Wear gloves and safety glasses. Crystals and strong solutions irritate skin and eyes and leave brown stains.
• Never mix with glycerine, sugar, oils, alcohol or other fuels. Some of these mixtures catch fire on their own.
• Never mix with concentrated acids, especially sulphuric acid, or with hydrogen peroxide. These reactions can be violent.
• Store in a tightly closed container in a cool, dry place, away from heat, combustible material, and acids.
• Keep away from children. It is harmful if swallowed.
• For small spills, sweep up dry crystals carefully without adding paper or sawdust. Leftover solution can be diluted with plenty of water; for larger amounts, follow local waste rules.
• Do not use it on fruits, vegetables, skin or for any medical purpose. These packs are sold for water treatment and lab use.

For a home well or tank, the 100 g technical pack lasts a long time because doses are small. Pick 300 g if you treat water regularly. Labs and colleges should buy extrapure, since impurities in technical grade throw off titration results; the 1 kg pack suits a department running practicals every week.

Remember the per-order and per-month limits on this chemical. Institutions and plants needing 25 kg or more can use our bulk inquiry form; we'll ask for documents where the rules require it.