Uses of Halogens
- Halogens and their compounds have a wide range of important industrial uses but also environmental significance
Purification of water
- Chlorine can be used to clean water and make it drinkable
- The chlorine kills bacteria which could cause infectious diseases
- It also prevents the growth of algae, removes bad tastes, smells and discolouration
- However, there are some concerns associated with the use of chlorine in water purification
- Chlorine is toxic
- It can also react with organic substances in the water and potentially cause carcinogens
Bleaches
- Chlorine is also widely used as a bleaching agent
- It reacts with oxygen and therefore reduces dyes and pigments to become colourless
- Household bleach is made up of dissolved calcium hypochlorite (Ca(OCl2)) and sodium hypochlorite (NaOCl) which act as disinfectant and cleaning agents
- During the manufacturing process of bleach, harmful toxins including chlorine gas are released into the atmosphere
- These pollutants stay in the air and cause pollution as well as damage the ozone layer
PVC
- Chlorine is used in the manufacture of the polymer polyvinyl chloride (PVC)
- PVC is a cheap and versatile polymer used for a wide range of purposes
- PVC is used for windows, drainpipes, electrical cable insulation and clothing
- However, PVC is very unreactive, so disposing of the polymer has a wide range of environmental consequences
- PVC is non-biodegradable and takes many years to break down
- Burning the PVC polymer release toxic fumes into the atmosphere
Use of halogenated hydrocarbons
- The most common halogenated hydrocarbons are chlorofluorocarbons (CFCs)
- These compounds contain carbon atoms with chlorine and fluorine atoms attached to them
- Eg. CCl3F and CCl2F
- CFCs have many uses due to their non-flammable and non-toxic properties
- They are used as refrigerators
- Propellants for aerosols
- As solvents for dry cleaning
- However, CFCs have adverse environmental effects
- CFCs absorb a lot of UV radiation in the upper atmosphere
- The CFCs are then broken down by the UV light causing the formation of chlorine radicals
- These radicals react with ozone and break down the ozone layer
- Halogenated hydrocarbons are also used in making plastics such as PVC (which is a polymer made from the monomer chloroethene)
