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

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

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.

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.

What is a disproportionation reaction?

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

Examples

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

Production

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.

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.

NaClO₃

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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