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517-579-3061 Teléfono en México: 55-5351-3093

Sodium Hypochlorite FAQ

Powell > Resources > FAQ > Sodium Hypochlorite FAQ

Frequently Asked Questions about Sodium Hypochlorite

What is Sodium Hypochlorite?

Sodium Hypochlorite Chemical Properties

Chemical Formula: NaOCl

Raw Materials: Chlorine, Sodium Hydroxide (Caustic)

Appearance: Greenish-yellow liquid

Specific Gravity: Sodium hypochlorite produced by a continuous process will have approximately 0.2% by weight excess sodium hydroxide, resulting in a specific gravity of 1.160 at 120 gpl

Decomposition: The presence of transition metal ions (copper and nickel) is known to catalyze the decomposition of liquid sodium hypochlorite, contributing to the loss of strength and the formation of oxygen. Loss of sodium hypochlorite strength means more product will be needed when the bleach is used as a disinfectant.

Common Uses for Sodium Hypochlorite

Sodium Hypochlorite is the main ingredient in laundry bleach. It is used extensively as a bleaching agent in the textile, detergents, and paper and pulp industries. It is also used as an oxidizing agent for organic products. In the petrochemical industry, sodium hypochlorite is used in petroleum products refining. Large quantities are also used as a disinfectant in water and wastewater treatment and sanitary equipment. In food processing, sodium hypochlorite is used to sanitize food preparation equipment, in fruit and vegetable processing, mushroom production, hog, beef and poultry production, maple syrup production, and fish processing.

In various parts of the world, sodium hypochlorite strength is identified using five common definitions listed below.

Terms used to Define Sodium Hypochlorite Strength

  • Grams Per Liter Available Chlorine
  • Grams Per Liter Sodium Hypochlorite
  • Trade Percent Available Chlorine
  • Weight Percent Available Chlorine
  • Weight Percent Sodium Hypochlorite

The chart below lists some of the varying strengths of Sodium Hypochlorite and how these solution strengths are typically used.

Note: The higher the sodium hypochlorite strength, the faster the decomposition rate becomes. See Decomposition of Sodium Hypochlorite for more information.

Sodium Hypochlorite Hazards/Precautions

  • Never mix Sodium Hypochlorite, with acidic solutions or Ammonia. Doing so forms a dangerous gas potentially leading to choking and breathing difficulty.
  • Avoid swallowing and getting sodium hypochlorite in the eyes or on the skin. Depending on the strength of sodium hypochlorite, severity can range from mild irritation to severe burns.
  • In the event sodium hypochlorite is swallowed, seek emergency help immediately. If the affected person is alert, give them milk or water to drink. Do not induce vomiting. Seek immediate medical attention.
  • Skin or eyes should be immediately flushed continuously and thoroughly if coming into contact with sodium hypochlorite. Seek immediate medical attention.
  • In the event of inhalation of sodium hypochlorite, leave the affected area and seek fresh air. If breathing is difficult, administer oxygen and seek immediate medical attention.

What is the Chemical Formula for Sodium Hypochlorite?

The chemical compound formula for sodium hypochlorite is NaOCl.

Reacting chlorine and sodium hydroxide will produce sodium hypochlorite:

Cl2 + 2NaOH = NaOCl + NaCl + H2O

How is Sodium Hypochlorite Made?

Sodium Hypochlorite is prepared by reacting dilute caustic soda solution with liquid or gaseous chlorine, accompanied by cooling.

Sodium Hypochlorite is commonly produced either through a batch process or through a continuous process.

What is the Specific Gravity of Sodium Hypochlorite?

The specific gravity of the sodium hypochlorite solution is the ratio of the weight of the solution with respect to water. If the product has a specific gravity of 1.2, a gallon of this sodium hypochlorite weighs 10.00 pounds (1.2 * weight of water). The specific gravity of sodium hypochlorite with the same strength may vary due to the amount of excess caustic in the solution.

Most tables that show strength and specific gravity of hypochlorite solutions were created 40-50 years ago. These levels are shown with excess sodium hydroxide (caustic) being much higher than the levels of sodium hydroxide typically produced by current manufacturers. Excess caustic levels have decreased over time due to improvements in manufacturing techniques.

The old tables will typically show 120 gpl available chlorine bleach with 0.73 % by weight excess caustic which results in a specific gravity of 1.168 at 20 degrees C. Typically, the sodium hypochlorite produced by a continuous process will have approximately 0.2% by weight excess sodium hydroxide and this would result in a specific gravity of 1.160. This number assumes very small levels of chlorate exist in the solution.

What is the Recommended Way to Store Sodium Hypochlorite?

Light, heat, organic matter, and certain transition metals (such as copper, nickel, and cobalt) accelerate the rate of decomposition of sodium hypochlorite. The presence of transition metal ions (copper and nickel) is known to catalyze the decomposition of sodium hypochlorite, contributing to the loss of sodium hypochlorite strength and the formation of oxygen. Loss of sodium hypochlorite strength means more product will be needed when the sodium hypochlorite is used as a disinfectant.

Oxygen build-up can pose problems when storing sodium hypochlorite in storage containers or sodium hypochlorite piping due to pressure build-up. By removing suspended solids to nearly undetectable levels, the rate of decomposition is significantly reduced. In addition, the formation of oxygen is nearly eliminated.

All sodium hypochlorite decomposition is dependent on temperature. For example, a 10°C increase in storage temperature will result in an increased rate factor of approximately 3.5.


Storage of sodium hypochlorite at approximately 60°F (15°C) will greatly reduce the decomposition of the sodium hypochlorite. Therefore, cooling the product before shipment will greatly reduce its decomposition.

It is relatively easy to chill the sodium hypochlorite with a chilled water system and plate heat exchanger. However, it is also possible to located storage tanks inside of an air-conditioned room if the tanks are relatively small.

Storage Tanks

Many different types of materials are used for construction of sodium hypochlorite storage tanks. Two common types of materials are linear or cross-linked polyethylene and fiberglass reinforced plastic (FRP). Other choices include chlorobutyl rubber lined steel and titanium. In some countries where these materials are not readily available, or the manufacturing quality is suspect, cubical concrete tanks lined with flexible plastic liners such as PVC have been successfully used. The choice of material depends on available capital, tank location, and required service life. Some tanks may only last 3-5 years. If properly specified and maintained, the tanks could last 10-15 years. The only material noted for over 30 year service life is titanium.

What Makes Filtered Sodium Hypochlorite Better than Non-Filtered Sodium Hypochlorite?

The filtering of sodium hypochlorite offers numerous advantages. Some of these advantages are as follows:

  • You can produce sodium hypochlorite using any quality of sodium hydroxide, including diaphragm cell caustic. This gives you a wider choice of suppliers which usually results in lower material cost and subsequent reductions in production costs.
  • You can sell your higher quality product at a higher price, a basic principle of supply and demand.
  • High purity sodium hypochlorite does not decompose as rapidly as standard grade, so you can reduce the strength of the product you produce.
  • Oxygen formation is significantly lower. As a result, product safety is improved allowing customers to package product without bottles swelling due to oxygen formation.
  • Costly customer quality complaints relating to oxygen and solids formation in storage tanks, pumps and piping are eliminated.
  • After filtration, sniff gas bleach can be sold as high-quality bleach.
  • Virtually all contaminants are removed during final filtration so most plant wastewater, including filter backwash water, containment area drains, water softener backwash and other wastewater can be reused to make bleach. Many plants using the Powell system have no wastewater connects to sanitary sewer systems.

What is the reason for Sodium Hypochlorite (Bleach) Decomposition?

Sodium hypochlorite decomposition rate is dependent on the total ionic strength of the product, temperature of the solution, pH, and transition metal content of the solution.

The primary pathway is 3NaOCl = 2NaCl + NaClO3

The minor pathway is 2NaOCl = 2NaCl + O2

What is the ideal pH of the solution?

The ideal pH of the solution should be from 11.86-13 pH or approximately 0.25% to 0.35% excess caustic (NaOH).

What is the decomposition rate of sodium hypochlorite?

Sodium hypochlorite has a second order decomposition rate. Therefore, reducing the concentration by half will reduce the decomposition rate factor by 5 assuming the products are at the same temperature.

What is the decomposition rate of sodium hypochlorite with respect to changes in temperatures?

For a 10°C increase in temperature, sodium hypochlorite at the same starting strength will decompose 3.5 times faster.

What is the effect of transition metals such as copper and nickel on sodium hypochlorite?

Transition metal (such as nickel and copper) increase decomposition. This decomposition produces oxygen. Concentrations below 50 ppb can typically be achieved with sub-micron filtration. Higher concentrations will cause unacceptable rates of decomposition.