Sodium Hypochlorite (NaClO) – Structure, Preparation and Uses

What is Sodium Hypochlorite(NaClO)? 

Sodium hypochlorite is a chemical compound with the chemical formula NaClO or NaOCl, comprising a hypochlorite anion (ClO⁻) and a sodium cation (Na⁺). It may also be called sodium hypochlorite acid salt. The anhydrous 10 sodium hypochlorite compound is unstable at room temperature. It may decompose explosively. The common name of sodium hypochlorite solution is bleach solution or “chlorine bleach”. It is widely used in textile mills.

Sodium hypochlorite solution is a strong oxidising agent that occurs as yellowish or greenish. It is commonly mentioned as chlorine bleach because of its active ingredient. Its chemical formula is NaClO, composed of one chlorine (Cl) atom, one sodium (Na) atom, and one oxygen (O) atom.

History of Sodium hypochlorite

In 1787, French chemist Berthollet discovered sodium hypochlorite in Javel on the outskirts of Paris as an active ingredient in household bleach. Its ability to productively whiten textiles was quickly uncovered and put to commercial use with great success. At the end of the 19th century, it became a disinfectant. It became famous after Louis Pasteur discovered sodium hypochlorite’s influential efficacy against disease-causing bacteria. Studies by various independent research academies have supported sodium hypochlorite’s high level of disinfection effectiveness. It is recognised as having an unmatched disinfection spectrum.

Structure of Sodium hypochlorite

Sodium hypochlorite is an ionic or electrostatic compound with the chemical formula NaOCl. On dissolving, it breaks as Na⁺ (cationic part) while OCl⁻ (as anionic part). The structure of the sodium hypochlorite molecule is given below. From its structure, it can be said that there is no direct bonding between Na⁺ and OCl⁻ ions. It is because they are not connected via any real bond. They are linked by an electrostatic force of attraction. While in a hypochlorite ion, a single chlorine atom is covalently bonded by an oxygen atom via mutually sharing a single electron pair.

 

Preparation of Sodium hypochlorite

1. Reacting chlorine with NaOH:

Sodium hypochlorite solution is obtained by passing Cl₂ into a cold and dilute solution of NaOH.

2NaOH (cold and dilute solution) + Cl₂ → NaOCl + NaCl + H₂O

2. By electrolysis of brine solution:

NaOH and chlorine gas are produced by the electrolysis of brine solution, which is then mixed to form NaOCl.

2Cl⁻ → Cl₂ + 2e⁻

2 H₂O + 2e⁻ → H₂ + 2HO⁻

3. By ozone:

Sodium hypochlorite can be obtained by reacting ozone with salt.

NaCl + O₃ → NaClO + O₂

This reaction can happen at room temperature and can be useful for oxidising alcohols.

4. From calcium hypochlorite:

Sodium hypochlorite solution is obtained by reacting sodium carbonate with calcium hypochlorite.

Na₂CO₃ (aq) + Ca(OCl)₂ (aq) → CaCO₃ (s) + 2 NaOCl (aq)

Characteristics of Sodium hypochlorite

The characteristics of sodium hypochlorite bleach are given below:

Physical properties of 10 sodium hypochlorite

• The molar mass of 10 sodium hypochlorite is 74.4 g/mol.
• The melting point of the pentahydrate form of sodium hypochlorite is 18°C. While on decomposition, the boiling point of sodium hypochlorite solution is 101℃.
• Its pentahydrate form is a greenish-yellow solid. 
• Sodium hypochlorite is soluble in water with a density of 1.11 g/cm³.
• Due to its high reactivity, it is highly corrosive.
• It has a chlorine-like and sweetish odour.
• Sodium hypochlorite is explosive and unstable, although sodium hypochlorite pentahydrate is non-explosive and stable at lower temperatures.

Chemical properties of 10 sodium hypochlorite

• When sodium hypochlorite solution is heated, it undergoes disproportionation into NaClO₃ and NaCl.

3NaClO → NaClO₃ + 2NaCl

• Atmospheric CO₂ liberates HClO from NaClO.

NaClO + CO₂ + H₂O → NaHCO₃ + HOCl

• When NaClO is heated with CaO in an alkaline solution, O₂ is liberated.

2NaOCl + CaO → 2NaCl + O₂

• It acts as a bleaching and oxidising agent as it produces nascent oxygen.

NaOCl → NaCl + [O]

• It oxidises H₂O₂ to O₂.

NaOCl + H₂O₂ → NaCl + H₂O + O₂

• It is used in the oxidation of starch.
• It has deodorising and bleaching properties.

Use of Sodium hypochlorite

For institutional and industrial applications, the versatility and use of sodium hypochlorite include:

• It controls algae in open reservoirs.
• The use of sodium hypochlorite is extensively used in water treatment to disinfect municipal drinking water and those taking drinking water from wells.
• It is used to disinfect the swimming pool water as a daily routine and shock treatment.
• It remains one of the most effective and cost-effective means of controlling the zebra mussel population, causing serious problems for industry and the ecosystem throughout North America.
• Chemical toilets and industrial waste for odour control.
• It is used to increase digestion efficiency and treat sewage to reduce odours.
• It aids in the treatment of cyanide effluent in gold mining.
• It treats cyanide waste in metal finishing.
• Food processing: fruit and vegetable processing, dairy equipment sanitising, hog, mushroom production, fish processing, maple syrup, and beef and poultry production.
• 12 Sodium hypochlorite is used for air scrubbing.
• It helps in treating cooling water and boiler water to prevent fouling.
• Sodium hypochlorite helps in precious metal recovery.

Sodium hypochlorite Side Effects

Some sodium hypochlorite side effects are

• Inhalation of sodium hypochlorite leads to coughing and irritation in the throat and lungs.
• Gulping down 10 sodium hypochlorite solution can cause a burning sensation, stomach pain, loose bowels, coughing, heaving, and an irritated throat.
• After prolonged exposure to sodium hypochlorite, the skin can get sensitive.
• It is harmful to water-based life forms.
• It causes pain and redness in the skin and eyes.
• It is carcinogenic and exceptionally poisonous when it interacts with ammonium salts.
• Ingestion of sodium hypochlorite solutions elicits vomiting and a destructive wound of the alimentary and digestive tract.
• Household bleaches (3 to 6% sodium hypochlorite solution) generally give rise to esophageal irritation. Still, they scarcely cause injuries or genuine injury, for instance, puncturing.
• Hypochlorite produces tissue injury by liquefaction necrosis.
• It is a dangerous and corrosive substance.
• Do not let sodium hypochlorite come into contact with the air. It is because that will cause it to disintegrate.
• Higher exposure to sodium hypochlorite may cause a fluid build-up in the lungs, leading to a medical emergency.

Role of Chlorine Bleach as a Disinfectant

Bleach, aka 12 sodium hypochlorite, mixed with water, produces oxygen. The oxygen produced by this process is nascent oxygen instead of dioxygen. It is not a normal oxygen molecule in the atmosphere. Nascent oxygen is more reactive than normal oxygen. Therefore, it can react to almost anything it comes into contact with.

In the water, on the floor, or wherever the bleach is applied, the oxygen produced during the reaction comes into contact with the microbes. As a result, it attacks the proteins that make up the cell wall. This attack causes the proteins to degrade, and the microbes die off once their cell walls are destroyed. The microbes cannot grow resistant to bleach unless they manage to produce an inert coating over them. Since this has not happened, bleach is still an effective disinfectant.

Conclusion

Sodium hypochlorite solution and its anhydrous form have a long history of safe use in hospitals, homes, and schools. It is widely available at a cheap price in the market. It has disinfecting and sanitising qualities, which are highly beneficial to good health and basic hygiene. It kills all investigated germs and a wider scope of bacteria than other disinfectants. It helps prevent disease spread through water and surfaces. Sodium hypochlorite side effects include its corrosive nature toward common container materials, skin burning, eye damage, and many other problems. Mixing 12 sodium hypochlorite with some household cleansers can be perilous.

Frequently Asked Questions

1. Can we substitute sodium hypochlorite with sodium chlorite?

A. No. Although sodium hypochlorite (NaOCl) and sodium chlorite (NaClO₂) are oxidisers, their chemical nature is quite different. NaOCl can act as a disinfectant and a bleaching agent, while NaClO₂ can be used to make chlorine dioxide (ClO₂). The chemical reaction that takes place is

2NaClO₂ + Cl₂ → 2ClO₂ + 2NaCl

This ClO₂ can be used as a bleaching agent or a disinfectant. Another difference is that hypochlorite is a ClO⁻ ion, whereas chlorite is a ClO₂⁻ ion. Their chemical behaviour is also different.

2. Why is bleach so effective in killing microorganisms?

A. Sodium hypochlorite bleach is typically approximately a 3% solution of sodium hypochlorite in the store-bought bottle. It has a pH of around 11. It is alkaline. Sodium hypochlorite bleach helps solubilise bacteria, organic dirt, and other living things. Although the most active part is the strong oxidising chemical activity of the hypochlorite, it attacks organic molecules by oxidising them and causing denature to them. As oxidising chemical reactions destroy living things, sodium hypochlorite bleach kills microorganisms effectively.

3. What happens to the pH value when sodium hypochlorite is added to water?

A. The water’s pH increases when sodium hypochlorite is added to it. It is because of the acidic soda present in the 12 sodium hypochlorite. When it dissolves in water, disinfection and oxidation are the two factors that play a major role.