Chemistry and Stability
- Sodium hypochlorite is an alkaline inorganic chemical compound with the chemical formula NaOCl.
- Its molar mass is 74.442 g/mol.
- It appears as a greenish-yellow solid in its pentahydrate form.
- Sodium hypochlorite is highly unstable in its anhydrous form and decomposes explosively.
- The decomposition is accelerated by carbon dioxide.
- It can be obtained as a stable crystalline pentahydrate and is stable when refrigerated.
- Sodium hypochlorite solutions can lose strength over time.
Equilibria and Decomposition
- Sodium hypochlorite is more stable in dilute solutions containing solvated Na and OCl ions.
- The density of the solution varies with concentration.
- Solutions are fairly stable at pH 11-12.
- Sodium hypochlorite can disproportionate to chloride and chlorate under certain conditions.
- This reaction occurs at high temperatures, forming sodium chlorate and sodium chloride.
- An alternative decomposition of hypochlorite produces oxygen instead of chlorate.
- The decomposition reactions are maximised at pH around 6.
Production Methods
- Reaction of sodium carbonate with chlorinated lime is a common method used in the past.
- Electrolysis of brine is another method that involves the electrolysis of brine to produce sodium hydroxide and chlorine gas, which are then mixed to form sodium hypochlorite.
- Production of solid stable dihydrate NaOCl·2H2O involves reacting chloride-free solution of hypochlorous acid with sodium hydroxide and removing sodium chloride by filtration.
- Concentrated slurries of the pentahydrate NaClO·5H2O can be produced using a similar principle.
- Sodium hypochlorite is packaged and sold under various trade names.
Uses and Applications
- Sodium hypochlorite is commonly used as a disinfectant and bleach.
- It is used in water treatment to kill bacteria and viruses.
- It can be used for stain removal and deodorizing.
- Sodium hypochlorite is used in the production of paper and textiles.
- It is also used in the pharmaceutical and food industries.
Environmental Impact and Safety
- Sodium hypochlorite has limited environmental impact as the hypochlorite ion degrades rapidly before being absorbed by living beings.
- Concerns arise from the formation of persistent chlorinated organic compounds, including known carcinogens, which can enter the food chain.
- Sodium hypochlorite should be handled with care as it can cause skin and eye irritation.
- It should not be mixed with other chemicals, especially acids, as it can release toxic gases.
- Proper ventilation and personal protective equipment should be used when handling sodium hypochlorite.
Sodium hypochlorite, commonly known in a dilute solution as (chlorine) bleach, is an alkaline inorganic chemical compound with the formula NaOCl (or NaClO), consisting of a sodium cation (Na+
) and a hypochlorite anion (OCl−
or ClO−
). It may also be viewed as the sodium salt of hypochlorous acid. The anhydrous compound is unstable and may decompose explosively. It can be crystallised as a pentahydrate NaOCl·5H
2O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.
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| Names | |
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| IUPAC name Sodium hypochlorite | |
Other names
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| Identifiers | |
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3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.028.790 |
| EC Number |
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| KEGG | |
PubChem CID | |
| RTECS number |
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| UNII | |
| UN number | 1791 |
CompTox Dashboard (EPA) | |
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| Properties | |
| NaOCl | |
| Molar mass | 74.442 g/mol |
| Appearance | greenish-yellow solid (pentahydrate) |
| Odor | chlorine-like and sweetish |
| Density | 1.11 g/cm3 |
| Melting point | 18 °C (64 °F; 291 K) pentahydrate |
| Boiling point | 101 °C (214 °F; 374 K) (decomposes) |
| 29.3 g/100mL (0 °C) | |
| Acidity (pKa) | 7.5185 |
| Basicity (pKb) | 6.4815 |
| Thermochemistry | |
Std enthalpy of formation (ΔfH⦵298) | -347.1 kJ/mol |
| Pharmacology | |
| D08AX07 (WHO) | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Oxidizer, corrosive |
| GHS labelling: | |
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| Danger | |
| H302, H314, H410 | |
| P260, P264, P273, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P391, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Safety data sheet (SDS) | ICSC 1119 (solution, >10% active chlorine) ICSC 0482 (solution, <10% active chlorine) |
| Related compounds | |
Other anions | Sodium chloride Sodium chlorite Sodium chlorate Sodium perchlorate |
Other cations | Lithium hypochlorite Calcium hypochlorite Potassium hypochlorite |
Related compounds | Hypochlorous acid |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Sodium hypochlorite is most often encountered as a pale greenish-yellow dilute solution referred to as liquid bleach, which is a household chemical widely used (since the 18th century) as a disinfectant or a bleaching agent. In solution, the compound is unstable and easily decomposes, liberating chlorine, which is the active principle of such products. Sodium hypochlorite is the oldest and still most important chlorine-based bleach.
Its corrosive properties, common availability, and reaction products make it a significant safety risk. In particular, mixing liquid bleach with other cleaning products, such as acids found in limescale-removing products, will produce chlorine gas, which was used as a chemical weapon in World War I. A common misconception is that mixing bleach with ammonia also releases chlorine, but in reality they react to produce chloramines such as nitrogen trichloride. With excess ammonia and sodium hydroxide, hydrazine may be generated.
sodium hypochlorite (uncountable)
