Sodium Hydroxide and Chlorine Gas Reaction | NaOH + Cl2

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.

Ways of reactions of NaOH + Cl2

There are two reactions can be happened according to the concentration and temperature of the sodium hydroxide solution.

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

Written by: Heshan Nipuna, updated:2020/05/17

Sodium hydroxide and chlorine gas reaction is completely different from sodium and chlorine gas 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 dilute 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 cglorine in OCl- ion is +1 and Cl- ion 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

This type of redox reaction balancing example is reaction of chlorine gas with ammonia.

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 gas.

Electrolysis of Brine (NaCl)

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


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 is 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.

Mechanism of Cl2 + dilute cold NaOH reaction

When chlorine gas dissolve in water, it produce hypochlorous acid (HOCl) and hydrochloric acid (HCl). You know acids react with bases and produce a salt and water as products. So when NaOH is in the presence of HOCl and HCl solution, following reactions are occurred.

  • HOCl and NaOH react and produce NaOCl and water.
  • HCl and NaOH react and produce NaCl and water as products.

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.


Ask your question now

As chlorine gas, will bromine and iodine react with sodium hydroxide?

We know bromine and iodine are less soluble than chlorine in water. Therefore, bromine and iodine do not react with sodium hydroxide as chlorine gas. That means, their (bromine and iodine) reaction rates are much slower than chlorine gas.

equation for the reaction between chlorine and hot concentrated alkali

We can denote the alkali as MOH in the equation. Chlorine (Cl2) is oxidized to chlorate (ClO3-) ion and chloride ion (Cl-) when it reacts with hot concentrated alkali.

3Cl2 + 6MOH → 5MCl + MClO3 + 3H2O

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 chlorine and NaOH 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.

What is chlorinated water or chlorination of water?

The process of adding chlorine or chlorine compounds such as sodium hypochlorite (NaOCl) to water. This is done in swimming pools. This is done to kill certain bacteria and other microbes in tap water as chlorine is toxic to those microbes. That's why we feel smell of chlorine gas in the swimming pools.

Chlorine reacts with hot and concentrated 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).

How this reaction is different from sodium hydroxide and HCl reaction?

NaOH and HCl reacts as base and acid respectively and produce salt (NaCl) and water as products. That reaction is not a redox reaction.

disproportionation reaction of water with sodium hydroxide

There is no disproportionation reaction oof water and sodium hydroxide. Only sodium hydroxide dissolve very well in water and dissociate to sodium ion and hydroxyl ions completely.

ocl- ion oxidation state?

We know electronegativity of oxygen is higher than chlorine. So negative charge should be on oxygen atom whole chlorine atom is oxidized due to higher electronegativity of oxygen. There is a single bond between oxygen and chlorine. Therefore oxidation number of chlorine is +1.

What will be the pH value after cold dilute NaOH reacts with chlorine gas if reactants are completely finished?

We know NaOH is a strong base. So it shows higher pH value which is greater than 7 at 250C.

How pH is calculated for a strong base?

When all NaOH reacts with all chlorine, there is no remaining NaOH and Cl2. Produced NaCl and NaOCl are in the solution and we should consider, whether their ability to hydrolysis of water to make water acidic or basic.

how does sodium hydroxide neutralize chlorine?

Use aqueous sodium hydroxide solution to neutralize chlorine gas. But commonly, spraying a solution of baking soda in water into the air or urea solution will be used. Cost of NaOH is very high.

Equipment to react chlorine with caustic soda?

Chlorine gas reacts with iron and produce ferric chloride. So we cannot use iron as the reactant container equipment.

Also, caustic soda slowly reacts with glass and form sodium silicate. So glass container is also not suitable for the reaction equipment.

Stability of NaCl

Sodium ion and chloride ion are stable in the water and do not involve in hydrolysis of water. So NaCl is a neutral salt.

Stability of NaOCl in water

Hypochlorite ion is not stable in water and involve in hydrolysis of water to prouce HOCl and OH- ion. So aqueous solution will basic due to release of hydroxyl ion.

Due to formation of OH- ions, aqueous solution gets basic and show pH values of greate than 7. But not much as aqueous NaOH solution.

Can I do NaOH, Cl2 reaction in the laboratory?

Yes. You can. You can prepare cold NaOH solution by using ice crystals or cold water. But, you will be find difficult to find chlorine gas in the laboratory. Then, you can try to make chlorine gas yourself. Mix dilute HCl solution and potassium permanganate solution. That will give Cl2 gas. Feed produced Cl2 gas safely through tubes to the NaOH solution.

reaction of chlorine with sodium hydroxide acid or base?

Reaction of chlorine with sodium hydroxide can be considered as an acid-base reaction. How do I say that?

First, chlorine dissolve in water and produce hydrochloric acid (HCl) and hypochlorous acid (HOCl). These two acids react with NaOH separately to give NaCl and NaOCl respectively.

sodium hydroxide react with chlorine to form bleaching powder, equation for reaction

Sodium hydroxide is not used in the production of bleaching powder. Ca(OH)2 reacts with chlorine to produce bleaching powder.

Reaction of caustic and chlorine

Caustic soda is a another name for NaOH. So reactions are same as NaOH and Cl2.

caution pool chorine naoh?

You may feel, smell of chlorine gas on swimming pools. This happens due to formation of chlorine gas from NaOCl which is added as a disinfectant.

chlorine gas and hydroxide

In the presence of hydroxyl ions (OH-) ions, chlorine gas is reduced to Cl- and oxidized to OCl- or ClO3- ion. The oxidation product depends on the concentration and temperature of the hydroxide solution. If temperature is high, chorine gas is oxidized to a its +5 oxidation state compound ClO3-.

Write a chemical equation for reaction between chlorine gas and dilute sodium hydroxide

NaOH + Cl2 → NaCl + NaClO + H2O

sodium and oxygen gas reaction?

If sodium piece is kept in the atmosphere, sodium readily reacts with oxygen and produce sodium oxide (Na2O). But, in the presence of oxygen gas stream, sodium gives sodium peroxide as the product. Sodium peroxide and sodium oxide both reacts with water to produce NaOH.

Which gas is produced when NaOH is prepared?

Chlorine and hydrogen gases are formed when concentrated aqueous NaCl is electrolyzed to produce NaOH. To prevent the reaction of chlorine and NaOH, a membrane is placed between cathode and anode.

sodium and chlorine reaction equation

2Na + Cl2 → 2NaCl

Chlorine and NaOH reaction have been included in following syllabuses.

  1. Cambridge International AS and A Level Chemistry
  2. General Certificate of Education (Advanced Level) GRADES 12-13

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