Sodium hypochlorite:-feature, application, working mechanism

Sodium hypochlorite(NaOCl)

Sodium hypochlorite is a clear, slightly yellowish solution with chlorine odour.


It is one of the disinfectants. So, it is useful in various applications

  • Water purification
  • Surface disinfection
  • The bleaching solution in the textile industry

Chemical reaction

NaOCl + H2O = HOCl + NaOH

When sodium hypochlorite is diluted with water it gives hypochlorous acid (chloric acid).  This is a weak acid which easily breaks and reconstructs to form free chlorine which is highly reactive and volatile in nature. Both of them are strong oxidizers.

Why sodium hypochlorite is used for hard cleaning?

When the sodium hypochlorite comes in contact with the bacteria, the oxidizing nature of the solution causes the breakdown of its protein. In case of coulter counter, when the blood runs through the tubes of the machine, the cell might undergo necrosis causing the accumulation of cellular contents in the tubes. This then quickly becomes the resting site of bacteria which will lead to the obstruction in the blood flow through the tubes and gives you fault reading. So, this is why a diluted form of NaOCl is used in coulter counter for hard cleaning.  

Dilution of sodium hypochlorite

As stated already, sodium hypochlorite should be diluted with water before use. You can find diluted NaOCl in the market. It might be of any concentration such as 5%, 3.5%, etc. So if you want to lower the concentration of the solution you can use the formula given below.

W1V1 = W2V2   where W1= concentration of an original solution

V1= volume of solution taken

W2= Concentration of diluted solution that you want to make

V2= Final volume of the diluted solution

For example, if you want to change 5% concentration of 10ml NaOCl to 2% concentration then you need to dilute it with 15 ml of water.

Handling of NaOCl solution

  • It should always be diluted by water, not by other diluents. Else, the chlorine might form dangerous compounds with it.
  • Chlorine is highly volatile, even at low temperature. So, it should not come in contact with sunlight. It should also not come in contact with acids, metals etc. This might lead to the formation of poisonous, corrosive gasses including chlorine gas. So, store it in a dark room, opaque bottles, etc.
  • Use it within 60 days after you have opened the container of the solution. Close the container tightly when not in use.
  • Since NaOCl is highly corrosive, its high concentration can corrode the machinery parts. It can cause a burning sensation to the human skin. If you are working with this solution make sure that you do not spill it on to your clothes. Else, it will immediately change the colour of your clothes to whitish. Because of this solution I had to buy 3 pants in just six months of my work. 
  • Wear masks, safety goggles, shoe cover, etc., for your safety.


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