Sodium hypochlorite

Sodium hypochlorite (CAS 7681-52-9), also referenced as NaOCl or sodium oxychloride, is an inorganic oxidizing agent.

Where is Sodium hypochlorite used?

• Water treatment: disinfection of potable water, biofilm control in cooling towers, wastewater effluent sanitisation
• Pulp and paper: bleaching of cellulose fibers via ECF and TCF sequences
• Food processing: surface sanitizer and equipment disinfectant at regulated concentrations
• Textile and laundry operations remove color from natural fibers and formulate bleaching liquors.
• In the agricultural and food industry, sanitizing and disinfecting equipment that contacts or does not contact food, as well as treating certain fruits and vegetables.
• On-site electrolysis is used in seawater desalination plants for sanitizing equipment and piping.
• Drinking water sanitation as a replacement for gaseous chlorine, which presents more handling and storage risk.

Good to know: Commercial concentrations typically range from 5% to 15% available chlorine; the 12–15% range is standard for industrial supply, while dilute 5% solutions are common in food-grade and institutional cleaning. Technical and food-grade designations are available, with specifications aligned to ANSI/AWWA B300 and international standards including FCC, USP, Ph. Eur., BP, EP, and ACS where applicable.

Formulation notes

• Loses antimicrobial activity in the presence of organic matter.
• Mixing with acidic solutions such as vinegar produces chlorine gas.
• Mixing with ammonia-based detergents produces toxic chloramine gas.

Typical specification

• Final product pH is maintained above 11 by an excess of unreacted sodium hydroxide between 0.5 and 1.5% by weight.
• A 12% sodium hypochlorite aqueous solution contains 9-16% w/w sodium hypochlorite.
• The solution also contains between 0.5 and 1.5% sodium chloride as a reaction by-product.
• To convert sodium hypochlorite concentration in % (weight) to ppm or mg/kg available chlorine, use the formula: % NaOCl × 10,000 ÷ 1.05 = available chlorine in ppm or mg/kg.
• On-site electrolysis-produced solutions have concentrations around 1%.

Regulatory status

• A specific concentration limit of EUH031 (contact with acids liberates toxic gas) applies at concentrations of 5% or more.
• To comply with Article 95, the manufacturer, supplier or distributor of the sodium hypochlorite solution must be listed for 'active chlorine released from sodium hypochlorite' in the relevant product type.
• Active chlorine released from sodium hypochlorite is classified as a 'releaser' rather than an in situ generated active substance under the Biocidal Products Regulation.
• Sodium hypochlorite carries H318: causes serious eye damage.

Storage, packaging and handling

• Reacts with urea to form the highly explosive compound nitrogen trichloride (NCl3).
• Maintaining an alkaline pH is essential for stabilizing the solution, because at acidic pH chlorine returns to its gaseous state and escapes from the solution.

Frequently asked questions about Sodium hypochlorite

What materials are incompatible with sodium hypochlorite?

Sodium hypochlorite is incompatible with cellulose-based absorbents and expanded polymeric absorbents. Mixing bleach with hydrogen peroxide creates a highly reactive mixture that can rapidly release oxygen gas, increasing risk of splashes, irritation, and explosions.

Is solid sodium hypochlorite commercially available?

Solid sodium hypochlorite is not used commercially, although it is possible to find it in this form.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.