Sodium Hydroxide and Chlorine Gas Reaction | NaOH + Cl₂

Aqueous Sodium hydroxide solution readily reacts with the Chlorine gas in two ways according to the concentration and temperature of the solution and gives different products depending on those parameters. Reaction between NaOH solution and Cl₂ gas is an Redox reaction (oxidation - reduction) and this reaction become more special because this is a disproportionation reaction. In this tutorial, we will discuss these facts in detail.

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Ways of reactions between NaOH and Cl₂ gas according to the temperature and concentration

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

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

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

In this section, we will discuss what products are given under specific conditions and the chemically balanced equation.

Products given by the reaction of cold dilute NaOH and Cl₂ gas reaction

Cold dilute sodium hydroxide and chlorine gas reaction is disproportionation reaction. Chlorine gas is oxidized and reduced to hypochlorite ion (OCl^-) ion and Chloride (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 solution which contains Sodium chloride (NaCl) and Sodium hypochlorite (NaOCl) is called as the Milton solution. Hypochlorite ion is an active anion and exists in the bleaching powder.

Stoichiometric equation (Chemically balanced) of cold dilute NaOH and Cl₂ gas reaction

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

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

Products given by the reaction of hot concentrated NaOH and Cl₂ gas reaction

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

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

Stoichiometric equation (Chemically balanced) of hot concentrated NaOH and Cl₂ gas reaction

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

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Stability of Hypochlorite ion | Chlorate(i) ion | OCl^-

Hypochlorite (OCl^-) ion is an unstable ion it is stable only in cold state conditions. When temperature increases, it disproportionate to chloride ion and chlorate ion. In Hypoclorite ion, negative charge is on the oxygen atom becuase oxygen is more electronegative than chlorine.

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Other halogens with aqueous sodium hydroxide solution

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

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How to Balance 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 chlorine 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 number of Sodium atoms in both sides. There are two Sodium atoms in the right side. So we make two number of NaOH.
• Then check the balance of number of hydrogen atoms. Left side has two hydrogen atoms so far now. Then only one H₂O molecule in the right side is enough to balance the number of hydrogen atoms in the equation.

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

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Mechanism of Cl₂ gas and dilute cold NaOH reaction

When chlorine gas dissolve in water and reacts with 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.

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Safety of NaOH and Cl₂ gas reaction

This reaction should be conducted in a safe manner to avoid any accidents because there are dangerous chemicals.

• NaOH is corrosive and may severely irritate skin, eyes, and mucous membranes. Also corrosive to the metals.
• Cl₂ is a yellow - green colour and extreemely toxic gas to humans. When you dealing with Cl₂, be very careful to get protected from it. Specially, avoid any Chlorine gas leakages to outside environment.

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Detailed summary of products and characteristics of the Reaction

Here, we discuss some special features and characteristics to this reaction.

A disproportionation reaction?

A reaction in which a substance is simultaneously oxidized and reduced, giving two different products. Reaction of NaOH and Cl₂ gas reaction, Hydrogen peroxide decomposition to water and O₂ gas are two examples.

Production of NaOCl and NaClO₃

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

Is something similar products will give Electrolysis of Brine (NaCl)

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

How to produce NaOCl?

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 to keep NaOCl stable.

How to produce NaClO₃?

Produced Cl₂ is sent to the hot concentrated NaOH.

In both occasions, NaCl is produced as a product. We can separate NaClfrom NaOCl or NaClO₃ by a separation method.

Questions asked by students

Ask your question and find the answer free.

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 produce 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 greater than 7. But this solution is not basic as an aqueous NaOH solution.

Can I do the experiment of 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.

Does Sodium and chlorine gas reaction gives the same products as Sodium hydroxide and chlorine gas give?

Sodium hydroxide and chlorine gas reaction is completely different from sodium and chlorine gas reaction.

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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