Sodium Hydroxide and Chlorine Gas Reaction | NaOH + Cl2

Sodium hydroxide reacts with chlorine gas in different ways according to the concentration and temperature of the solution and it gives different products. NaOH and Cl2 reaction is an oxidation - reduction reaction and those reactions are more special because they are disproportionation reactions.

Reaction Types of NaOH + Cl2

  • Cold dilute NaOH and Cl2 reaction
  • Hot concentrated NaOH and Cl2 reaction

Cold Dilute NaOH and Cl2 reaction | NaOH + Cl2 = NaCl + NaOCl + H2O

Cold dilute sodium hydroxide and chlorine gas reaction is disproportionation. Chlorine gas is oxidized and reduced to OCl- ion and Cl- ion respectively. As products sodium chloride, sodium chlorate(i) and water are given.

  • Hypochlorite ion | chlorate ion(i) - OCl-
  • Sodium chloride - NaCl
  • Sodium chlorate(i) - NaOCl

Aqueous NaCl, NaOCl solution is called as the Milton solution. Hypochlorite ion exists in bleaching powder.

Chemical Balanced Equation

cold dilute NaOH + Cl2

In hypochlorite ion, chlorine atom is in the +1 oxidation state. In NaCl, chlorine is at -1 oxidation state.

Hot concentrated NaOH and Cl2 reaction | NaOH + Cl2 = NaCl + NaClO3 + H2O

Hot dilute sodium hydroxide and chlorine gas reaction is also a disproportionation reaction.Chlorine gas is oxidized and reduced to ClO3- ion and Cl- ion respectively. As products sodium chloride, sodium chlorate(iii) and water are given.

  • Chlorite ion - ClO3-
  • Sodium chlorate(iii) - NaClO3

Chemical Balanced Equation

Hot concentrated NaOH + Cl2

In chlorite ion, chlorine atom is in the +5 oxidation state.

Hypochlorite | Chlorate(i) ion | OCl-

OCl- ion is an unstable ion it exists only in cold states. When temperature increases, it disproportionate to chloride ion and chlorate ion. Negative charge is on the oxygen atom.

hypochlorite ion disproportionate

As chlorine gas, other halogens except fluorine also react with sodium hydroxide and give similar products as NaOH + Cl2 reaction.

Balancing the cold NaOH and Cl2 reaction

We know this reaction is a disproportionation reaction. When we see the products, it's clear that Cl2 is oxidized to OCl- and reduced to Cl-. Oxidation numbers of Cl in OCl- is +1 and Cl- is -1.

Now check the differences of each oxidation numbers in oxidation and reduction. It is one in both. Then exchange the differences.

Then balance other elements. Check Na atoms in both sides. There are two Na in the right side. So we put two in front of NaOH. Then check hydrogen balance. Left side has two hydrogen atoms so far now. Then only one H2O molecule in the right side is enough to balance the hydrogen equation.

NaOH + Cl2 = NaCl + NaOCl + H2O equation balancing

What is a disproportionation reaction?

A reaction in which a substance is simultaneously oxidized and reduced, giving two different products.


  • NaOH + Cl2 reaction
  • Hydrogen peroxide decomposition to water and O2


Now we need to produce NaOCl and NaClO3. So we need NaOH and Cl2

Electrolysis of Brine (NaCl)

Electrolysis of brine solution will produce NaOH, Cl2 gas and H2 gas.


We can collect Cl2 gas can cool the gas before send it to the produced NaOH to occur the reaction. NaOH solution also should be cold.


Produced Cl2 s sent to the hot NaOH.

In both occasions, NaCl is produced as a product. We can separate it by a separton method from NaOCl or NaClO3.

Safety of NaOH + Cl2 reaction

This safery and harmful facts are both valid for reaction of Cl2 with hot NaOH and cold NaOH.

  • NaOH is corrosive and may severely irritate skin, eyes, and mucous membranes. Also corrosive to the metals.
  • Cl2 is a yellow - green toxic gas. When you dealing with Cl2, be very careful to get protected from it.

What will happen, when Cl2 gas is sent to the water?

Cl2 hydrolysis in the water. HCl and HOCl are given as products. HCl is a strong acid and HOCl is a weak acid. HOCl is a very good disinfectant and more efficient than bleaching powder.

Can I use this NaOH + Cl2 reaction to neutralize Cl2 gas?

Yes. You can use NaOH and this is very efficient way to do the neutralization. But you have to consider about the cost of this neutralization method because NaOH is so expensive.

Chlorine reacts with hot and conc. NaOH, But why products are different?

When temperature is high, the ability to oxidation is high. Therefore produced NaOCl is oxidized to NaClO3< from +1 to +5 (oxidation umber of chlorine).

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