How Does Bleach Work Chemically?

25th November 2020

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How does bleach work chemically? Well, by disintegrating the molecular bonds of stains, which effectively removes those stains. How bleach works is actually a simple oxidation reaction that removes electrons from chromophores, otherwise known as pigment molecules. 

This article explains the chemistry behind this everyday substance, from the different types of chemical-based bleaches to the chemical makeup of bleach. 

Household chemicals, disinfectant, bleach, antibacterial gel, yellow rubber gloves, sponge, rags, dishwasher tablets on blue background.

What’s The Chemical Name For Bleach?

The chemical name for bleach is sodium hypochlorite (NaClO), a chlorine compound that has excellent disinfectant properties. It may sound intimidating, but even liquid bleach products that are commercially available for households are diluted solutions of NaClO, as well as secondary ingredients. This is the most common type of bleach you’ll find on the market.

The active sodium hypochlorite ingredient in bleach usually has around 5% concentration, while industrial grade liquid bleach products have higher concentrations. However, there are many other types of bleach that can be generally classified into three major categories: chlorine-based, peroxide-based, and sulfur dioxide-based bleaches. Most household and industrial bleaches belong to one of these categories, so the chemical name for bleach will depend on which category the product belongs to. 

Chlorine-Based Bleaches

Bleaches in this category rely on the decomposition of chlorine compounds to destroy the molecular bonds in pigment molecules. Examples of chlorine-based bleaches include:

  • Sodium hypochlorite: This is usually sold as a liquid bleach solution in water, typically with a 5- 6% concentration by weight. This chemical is also commonly used as a disinfectant because of its ability to denature proteins in microorganisms and kill bacteria and viruses.
  • Bleaching powder: This is a mixture of several chemicals, including calcium hypochlorite, calcium hydroxide, and calcium chloride. Also known as chlorine powder or chlorinated lime, this isn’t only used as a bleaching agent, but also as a water treatment.
  • Chlorine gas: This is commonly used to treat municipal tap water as well as large swimming pools. It can also be used for bleaching wood pulp on an industrial scale, but this practice has significantly declined in recent years because of environmental concerns and chemical manufacturing regulations.
  • Chlorine dioxide: This is unstable in its gaseous form and so is stored as a dilute aqueous solution. Chlorine dioxide is widely used for bleaching wood pulps in the paper industry. It’s also used to bleach fats and oils, textiles, bee wax, and animal skin.
Structural chemical formula of sodium hypochlorite with cleaning products.
The chemical name for bleach is sodium hypochlorite (NaClO)

Peroxide-Based Bleaches

The active agent of peroxide-based bleaches is oxygen. So how does bleach work chemically when chlorine isn’t involved? Well, in these formulations, the bleaching action relies on the decomposition of hydrogen peroxide, or other peroxide compounds. Some common examples of peroxide bleaches are:

  • Hydrogen peroxide: This is commonly used as an antiseptic for wounds, though hydrogen peroxide has many other uses besides this, including as a lightening agent in cosmetics and hairdressing. On an industrial scale, it’s used to bleach wood pulp and to prepare other types of bleaching agents, like perborates and percarbonates.
  • Sodium percarbonate: This is an adduct of two chemicals, namely hydrogen peroxide and sodium carbonate. When dissolved in water, sodium percarbonate produces a solution that can simultaneously be used as a bleaching agent and as a degreaser.
  • Sodium perborate: When this is dissolved in water, some amount of hydrogen peroxide is produced. Its bleaching action is dependent on the decomposition of hydrogen peroxide and the nucleophilic oxidation of the perborate anion.
  • Peracetic acid: This is also known as peroxyacetic acid and it can be highly corrosive. Peracetic acid is produced by laundry detergents when dissolved in water, and it’s sold on the market for industrial and agricultural disinfection purposes
  • Benzoyl peroxide: Although commonly used as a medication treatment for acne, benzoyl peroxide is actually classed as a food additive. In fact, the bleaching action of benzoyl peroxide is mainly used to bleach flour because of its ability to oxidise flour’s carotenoids.
  • Persulfate salts: These are very strong oxidisers that are commonly used in powdered hair-lightening products. Examples of persulfate salts are potassium persulfate, ammonium persulfate, and sodium persulfate.

Sulfur Dioxide-Based Bleaches

This type of bleach has sulfur dioxide as the active ingredient, the bleaching action of which is accomplished through the chemical decomposition of oxo sulfur anions. 

Sodium dithionite, also known as sodium hydrosulfite, is the most common and important example of sulfur dioxide-based bleaches. It’s sold as a white crystalline powder that has a slightly sulphurous odour. This bleach product is produced by the reaction of sodium bisulfite with zinc. 

Stylist preparing a hair dye in a container
Hyrdogen peroxide-based bleaches can be used to lighten hair

What’s The Chemical Formula For Bleach?

There’s actually no single chemical formula for bleach, simply because of how many different types of bleach there are. Each category of bleach is composed of distinct chemicals, and these are what determines its chemical formula, as well as how different bleach products work chemically. Here are some examples of various bleach products to show how the chemical formulas can change:

  • Sodium hypochlorite: NaClO
  • Calcium hypochlorite: Ca(ClO)
  • Calcium hydroxide: Ca(OH)2
  • Calcium chloride: CaCl2
  • Hydrogen peroxide: H2O2
  • Sodium percarbonate: Na2H3CO6
  • Potassium persulfate: K2S2O8

What’s The Chemical Makeup Of Bleach?

Now for the real question of how does bleach work chemically. The chemical makeup of bleach can be determined by looking at its action. Chemically, all types of bleach act as proton acceptors – this is why bleach is called nucleophilic, i.e. lover of nucleus. In a nutshell, bleach products oxidise other substances by removing the outer electrons and then attracting the proton in the nucleus.

In effect, the molecular bonds of the chemicals that bleach attacks, particularly the chromophores (those pigment chemicals), are broken by the chemicals inside the bleach. The same actions occur when bleach molecules touch the cell membranes of viruses and bacteria: the pathogens are ruptured, which kills them and prevents infection.

Bleach is also a basic, or alkaline, substance. For instance, the most common type of liquid bleach is a dilute aqueous solution of sodium hypochlorite, which typically has a pH of 11 when used at 5% concentration. At higher concentrations, the pH level can rise to 13. This is why high concentrations of bleach can be so corrosive, especially given that strong bases have the ability to penetrate surfaces deeply.

Bleach Chemical Structure Explained

As alkaline or basic substances, all types of bleach are highly polar molecules because of the way they’re bonded. These types of bonds may differ from product to product, such as the ionic bond of sodium hypochlorite molecules compared to the weak covalent bond of hydrogen peroxide.

The polarity of bleaches is determined by the geometry of molecules, particularly the angle of bonds and by the way electrons are distributed. In the case of sodium hypochlorite, the ionic bond makes the sodium atom positively charged, while the chlorine and oxygen group are negatively charged.

An example of a bleach compound that is polar because of the bond angle is hydrogen peroxide. Here, the bonds render the molecule in a zigzag shape: the two oxygen atoms form a straight line at the centre of a plane with a 147.4 picometre distance from each other. Meanwhile, the two hydrogen atoms have the same 95 picometre distance from their respective oxygen atoms. The interior angle between the oxygen and hydrogen atom is 94.8 degrees.

Applications Of Bleach

Bleach products have a variety of industrial and household applications. While they’re perhaps most commonly used as a cleaning agent for bathrooms, kitchens and laundry, some types of bleach are used in the beauty and cosmetics sector as a lightener, whether it’s for hair, nails or even skin. 

Higher concentrations of bleach can be used on an industrial level to disinfect water that’s polluted with contaminants and pathogens. Other types of industrial-scale bleach have a wide range of uses in paper manufacturing, such as to bleach wood pulp. 

No matter how you’re using it, bleach can be very corrosive, so care should always be taken when handling this chemical.

Disclaimer

All content published on the ReAgent.co.uk blog is for information only. The blog, its authors, and affiliates cannot be held responsible for any accident, injury or damage caused in part or directly from using the information provided. Additionally, we do not recommend using any chemical without reading the Material Safety Data Sheet (MSDS), which can be obtained from the manufacturer. You should also follow any safety advice and precautions listed on the product label. If you have health and safety related questions, visit HSE.gov.uk.

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