Chlorine is typically used either as a solution or as a part of a compound like sodium hypochlorite (NaClO). As a strong oxidising agent, it’s very useful as a disinfectant even at very dilute concentrations. For instance, it’s commonly used as a swimming pool disinfectant at a concentration range of between 1.0 and 3.0 parts per million (ppm).
Chlorine is a highly corrosive gas that reacts readily with many substances. It has an atomic number of 17 and a standard atomic weight of 35.45. It belongs to the group of elements known as halogens, which are all highly reactive and harmful, or even lethal to biological organisms because of their ability to strip substances of their outer electrons.
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Everyday Uses of Chlorine
Free or elemental chlorine rarely occurs in nature, except for the very small amounts that can be found in volcanic gases. Even in this case, this element eventually reacts with other substances to form compounds, which is why it’s usually found in small concentrations in everyday substances like cleaning agents, healthcare products, and pool disinfectants.
Chlorine is mainly found as a constituent in other compounds or solutions. For example, it is commonly found in aqueous solutions of sodium hypochlorite, or as the active ingredient in household cleaning agents. This is why it is so often seen in cleaning chemical manufacturing, to name but one sector.
While the main industrial and commercial use of this substance is as a disinfectant, it has plenty of other uses, such as in bleaching agents and even renewable energy production. Here are some everyday uses of chlorine:
- Swimming pool disinfectant: While chlorine by itself isn’t used to disinfect swimming pools, a solution of a compound that contains it, such as sodium hypochlorite, is commonly used. In the case of sodium hypochlorite, this is an inorganic salt that has a hypochlorite group as the counterion of sodium. As an aqueous solution, the sodium and hypochlorite split into ions, making the hypochlorite highly oxidative so that it can strip electrons from the cell membranes of bacteria and other microorganisms in the swimming pool water.
- Household disinfectant: Many household cleaning agents have chlorine-based compounds as the active ingredients. Some products are concentrated and need to be diluted with water. For example, you can use a 5% proportion of a chlorine-based cleaning agent to clean surfaces like tables, countertops, and floors.
- Building and construction: Building insulation is usually made from plastic foams using chlorine chemistry. They reduce energy consumption by preventing heat inside the house from escaping during cold weather. Conversely, the heat from the outside is prevented from baking the inside of the house during hot days. Chlorine compounds are also used in manufacturing durable paints.
Key Takeaways
Chlorine is widely used as a disinfectant in household cleaners, swimming pools, and for tap water in small doses due to its strong oxidising properties
As a halogen, chlorine’s reactivity makes it a powerful oxidising agent, useful in diverse applications but also hazardous in high concentrations
Chlorine plays a role in manufacturing plastics (e.g. PVC), insulation, and durable paints, contributing to construction and energy efficiency
Chlorine is involved in oxidation reactions, chemical synthesis, and experiments; it is also a byproduct of electrolysis and other chemical reactions
Why is Chlorine Added to Swimming Pools?
Although pools have continually flowing water running through pipe systems and drains, dirt accumulates in them quickly. From hair and shedded skin cells to fallen leaves, various types of contaminants accumulate in pools and risk the health of pool users.
The most dangerous types of contaminants in swimming pools are pathogenic microorganisms, such as bacteria and fungi. Although viruses are technically not alive, some may still contaminate pools and potentially infect swimmers.
With this in mind, chlorine is added to swimming pools to kill the pathogenic microbes in the water. Generally, the chlorine level in a swimming pool should be maintained between one and three parts per million for hygiene reasons.
Is Chlorine Added to Tap Water?
Yes, chlorine is added to tap water. This practice is a cornerstone of public health, ensuring that drinking water is as free as possible from harmful bacteria and viruses. Without chlorine, waterborne diseases such as cholera and typhoid could easily spread, posing serious health risks.
Chlorine is added in very small amounts to drinking water, carefully monitored to balance safety and effectiveness. Beyond disinfection, it also helps maintain water quality during its journey through pipes and reservoirs, making sure it remains safe until it reaches your tap.
The tap water that we use everyday is from three sources: rivers, groundwater, and reservoirs seawater. Regardless of the source, chlorination is a key part of the water treatment process.
Scientific Applications for Chlorine
Gaseous elemental chlorine can be prepared in a laboratory through several methods, such as the reaction between an acid that contains chlorine and a metal oxide. This element can also be prepared in the laboratory through the electrolysis process. Consider the following chemical reactions:
- Double displacement reaction
The reaction of manganese dioxide with hydrochloric acid is a double-displacement reaction that releases chlorine gas. One mole of manganese dioxide reacts with four moles of hydrochloric acid to produce one mole of manganese (II) chloride, two moles of water, and one mole of chlorine.
- Electrolysis reaction
The electrolysis process is used both in the laboratory and in the factory to produce chlorine, as can be seen illustrated below:
How is Chlorine Used in Chemistry?
Chlorine has many uses, from an ingredient in chemical mixing to being the primary reagent. One key use is as a disinfectant because of its high reactivity as an oxidising agent. It can easily strip away the outer electrons of almost any substance, including the outer phospholipid membranes of bacteria and other microorganisms. This substance is so corrosive that it was weaponised during World War I due to its ability to destroy the mucus membranes of the lungs.
Chlorine belongs to the group of elements known as the halogens, which include five additional elements:
- Fluorine (F)
- Bromine (Br)
- Iodine (I)
- Astatine (At)
- Tennessine (Ts)
Looking at column 17 of the periodic table of elements, chlorine is second from the top. The respective position of the halogens from top to bottom also indicates their reactivity. Although the five halogen elements are chemically similar, their relative reactivity increases from bottom to top. For instance, fluorine can oxidise chlorine:
Using Liquid Chlorine in a Lab
Chlorine is a greenish yellow gas at room temperature, but it becomes a liquid at −34 °C. It’s the most compressible element, making it relatively easy to transport in pressurised liquid form. About one-half kilogram of liquid chlorine can suddenly expand to 142 litres of gas when released. About one-half kilogram of liquid chlorine can expand to 142 litres of gas when released.
Liquid chlorine can also refer to an aqueous solution of sodium hypochlorite. In either case, the liquid form of this substance can be used in several ways in a lab, such as in oxidation reaction experiments or in the preparation of polymers.
Chlorine in Manufacturing
Chlorine’s industrial applications are as varied as they are essential. It plays a central role in the production of materials and processes that underpin modern life, from plastics to pharmaceuticals.
Globally, about 58 million metric tonnes of chlorine are produced each year through the chlor-alkali membrane electrolysis process. The balanced chemical equation for this reaction is as follows:
Aside from disinfection purposes, this substance is also used as precursor, reagent, and ingredient in the synthesis of many substances. It’s also an excellent oxidising agent, and makes up a vital part of several industries:
Chlorine in Plastic Manufacturing
Chlorine is one of the sustainable ingredients in the manufacturing of plastics. For instance, polyvinyl chloride, or PVC, is unlike other types of plastics, which are manufactured wholly from fossil fuel. By comparison, PVC is 57% chlorine that’s obtained from sodium chloride or common salt.
PVC is commonly obtained from the reaction of ethylene with oxygen and hydrogen chloride by using copper as a catalyst. This packaging is durable, resistant to contamination, and essential for long-term storage.
Chlorine in Sewage Treatment
Adding chlorine to wastewater is a part of several steps in sewage treatment. Chlorination is necessary to kill pathogens and parasites in the sewage, remove bad odour, and balance the chemistry of the water. In the UK, the wastewater treatment process can be explained in five stages:
- Movement: This simply refers to ensuring that the wastewater reaches the sewage works. It involves drains and sewers
- Preliminary screening: The removal of large non-biodegradable solid waste materials
- Primary settlement: The process of separating suspended solids from the water
- Secondary sewage treatment: The microscopic biodegradable particles in the water are decomposed by bacteria
Tertiary treatment: This stage includes chlorination. The water is already clean but it is further treated to kill any pathogen. Minerals and other chemicals are also removed.
Chlorine in Fabric and Paper Production
Chlorine plays a pivotal role in the bleaching process for fabrics and paper, ensuring the final products are bright, clean, and suitable for their intended use.
Its ability to break down and remove unwanted pigments and impurities makes it indispensable in these industries. Here’s how chlorine is used in both examples:
Fabric Production:
- Preparation: The raw fabric is cleaned to remove surface dirt and oils.
- Chlorine Bleaching: Chlorine, typically in the form of a liquid solution or hypochlorite, is applied to the fabric. The chlorine reacts with the pigments and impurities, breaking down the colour and leaving the fabric whiter.
- Neutralisation: After bleaching, the fabric is treated with an anti-chlorine agent, such as sodium thiosulfate, to stop the chemical reaction and prevent damage to the material.
- Rinsing: The fabric is then rinsed multiple times to remove any residual chemicals and ensure it is safe for further processing or dyeing.
- Drying and Finishing: The bleached fabric is dried and finished with treatments like softening agents to enhance texture and quality.
Paper Production:
- Pulp Preparation: Wood or recycled paper is broken down into a slurry called pulp, which contains lignin, the compound responsible for the natural brown colour.
- Chlorine Treatment: Chlorine is introduced to the pulp, often as chlorine dioxide. It reacts with the lignin, breaking its chemical bonds and dissolving it.
- Washing: The pulp is washed to remove dissolved lignin and any byproducts of the bleaching process.
- Repeat Bleaching: For higher-quality or whiter paper, the bleaching process may be repeated multiple times.
- Drying and Finishing: The bleached pulp is pressed, dried, and processed into the final paper product, whether it’s office paper, packaging, or another type of paper product.
Chlorine in Pharmaceuticals
Chlorine is a vital component in the pharmaceutical industry. It is used to create active ingredients in medicines like antibiotics and antiseptics.
Its reactivity allows it to form essential compounds, as well as working to help with:
- Synthesis of chlorinated compounds: Chlorine is used to create chlorinated intermediates, which are building blocks in drug production. For example, antibiotics like chloramphenicol are synthesised using chlorine-containing compounds.
- Disinfection of equipment and facilities: Chlorine-based disinfectants are used to sterilise equipment and surfaces.
- Purification of raw materials: Chlorine is used to treat raw materials, removing impurities that could compromise the quality or effectiveness of the medicine. For example, chlorine compounds may be used to purify water or solvents.
- Quality control testing: Chlorine-based reagents are sometimes used in analytical tests to verify the composition and purity of pharmaceutical products.
Conclusion
Chlorine is a remarkably versatile element, with uses spanning from everyday hygiene to advanced scientific research and large-scale industrial processes. It ensures clean swimming pools, safe drinking water, and effective cleaning products while also being vital in chemistry and manufacturing.
While its applications are incredibly diverse, the common thread is chlorine’s ability to safeguard health, enhance convenience, and support progress.
