Sodium hypochlorite is a chemical compound with the formula NaClO. It is a pale greenish-yellow liquid that is commonly used as a bleach, disinfectant, and oxidizing agent. Sodium hypochlorite is produced by dissolving chlorine in sodium hydroxide and it releases free chlorine when added to water. It is widely used in the household, water treatment, and industrial sectors for cleaning, sanitizing, and purifying purposes. However, exposure to concentrated sodium hypochlorite solutions can cause skin and eye irritation, and inhalation of its fumes can cause respiratory distress, so it should be handled with care.
Chemistry
Stability of the solid
Sodium hypochlorite in solid form is highly reactive and unstable, with a tendency to decompose over time, particularly in the presence of heat, light, and impurities. This can cause the release of dangerous chlorine gas and a reduction in the concentration of sodium hypochlorite. Therefore, it is important to store solid sodium hypochlorite in a cool, dark place in well-sealed containers, and to use it promptly after it has been prepared.
Equilibria and stability of solutions
Sodium hypochlorite is a strong oxidizing agent, and its stability in solution depends on several factors, including pH, temperature, light exposure, and the presence of impurities such as heavy metals and organic matter. In basic solutions, sodium hypochlorite is relatively unstable, as it can react with hydroxide ions to form sodium hydroxide and hypochlorous acid. In acidic solutions, sodium hypochlorite is more stable, as it reacts with hydrogen ions to form hypochlorous acid and sodium ions. Light exposure can also affect the stability of sodium hypochlorite, as the ultraviolet (UV) light in sunlight can decompose the compound. Therefore, sodium hypochlorite solutions are typically stored in dark containers and protected from light exposure. Impurities such as heavy metals and organic matter can also decrease the stability of sodium hypochlorite by catalyzing its decomposition.
Decomposition to chlorate or oxygen
Sodium hypochlorite is a reactive substance that can decompose over time, forming either chlorate or oxygen. Decomposition of sodium hypochlorite can occur due to exposure to heat, light, or high temperatures. The reaction rate can also be influenced by the presence of contaminants such as heavy metals or acids. Decomposition can reduce the concentration of the active ingredient in the solution, lowering its efficacy as a bleach and sanitizer. To extend the shelf life and maintain the stability of sodium hypochlorite, it is often stored in dark containers and with pH control agents.
Uses
Sodium hypochlorite is commonly used as a bleach, disinfectant, and oxidizing agent in various applications including:
- Water treatment: Sodium hypochlorite is used in water treatment plants to purify water and eliminate harmful microorganisms.
- Laundry: Sodium hypochlorite is used as a whitening agent in laundry detergents.
- Sanitation: Sodium hypochlorite is used to sanitize and disinfect surfaces, including countertops, toilets, and floors.
- Swimming pools: Sodium hypochlorite is used to sanitize swimming pools and hot tubs.
- Textile industry: Sodium hypochlorite is used to remove dye from fabric.
- Food and Beverage Industry: Sodium hypochlorite is used for sanitizing equipment and surfaces in the food and beverage industry.
Safety
It is estimated that there are about 3,300 accidents needing hospital treatment caused by sodium hypochlorite solutions each year in British homes (RoSPA, 2002).
Sodium hypochlorite is a hazardous chemical and must be handled with care to avoid potential health and safety risks. The dangers of sodium hypochlorite include:
- Irritation: Sodium hypochlorite is an irritant to the skin, eyes, and respiratory system. Contact with the skin or eyes can cause redness, itching, and pain.
- Corrosiveness: Sodium hypochlorite is highly corrosive and can cause chemical burns if it comes into contact with skin or other tissues.
- Toxicity: Sodium hypochlorite is toxic if ingested or inhaled in high concentrations. It can cause respiratory distress, gastrointestinal symptoms, and other symptoms.
- Reactions with other chemicals: Sodium hypochlorite can react with other chemicals to produce toxic or flammable gases. This can pose a risk if not handled properly.
To minimize the risk of injury or illness, it is important to follow proper safety procedures when working with sodium hypochlorite. This may include wearing protective clothing and eye protection, using gloves, and avoiding skin or eye contact with the chemical. In the event of exposure, it is important to seek medical attention as soon as possible.
Oxidation and corrosion
Sodium hypochlorite is a strong oxidizing agent and can cause corrosion and oxidation of materials that it comes into contact with, such as metal pipes, storage tanks, and equipment. The risk of corrosion is greater in the presence of high temperatures, high levels of organic matter, and low pH levels. To minimize these risks, it is important to use materials that are compatible with sodium hypochlorite, such as PVC, and to take steps to prevent contamination of the solution by organic matter and to maintain proper pH levels. Additionally, it is important to follow proper safety protocols when handling and storing sodium hypochlorite, including wearing appropriate personal protective equipment and properly labeling containers.
Storage hazards
Sodium hypochlorite is a strong oxidizing agent and can cause fire and explosion if it comes into contact with organic materials, reducing agents, or metals. It is also a strong irritant to the skin and eyes, and should be stored in a cool, well-ventilated place, away from heat and ignition sources. Sodium hypochlorite is commonly stored in a brown, opaque plastic or glass container to minimize light exposure, which can cause the solution to decompose. When handling sodium hypochlorite, it is important to wear protective gloves, eye protection, and clothing to avoid skin and eye irritation, and to avoid inhaling the fumes. If sodium hypochlorite spills on clothing or skin, it should be immediately rinsed with water.