Water from different sources is treated with different methods depending on its origin and intended use.
Suspended matter is commonly removed from water by flocculation, followed by sedimentation and filtration.
The surface of fine silicate and aluminosilicate particles in clays is negatively charged and can be flocculated into larger particles by the addition of salts containing highly charged cations such as aluminium ions or polymers.
- Explain the use of aluminium ions and polymers in flocculating clay particles suspended in water.
Hard water contains high concentrations of Ca2+ and Mg2+ ions. Hard water renders soaps less effective and causes build-up of precipitates.
Natural and modified zeolites can be used in the purification and softening of water, through the exchange of cations.
- Explain the use of zeolites in water softeners.
Infographic: Soap versus body wash
Reverse osmosis is a filtration technique whereby water is forced, under pressure, through a semi-permeable membrane.
- Explain how reverse osmosis produces potable water from saline water.
Video: Reverse Osmosis
Desalination is a process used to remove minerals from saline water to produce fresh potable water. Reverse osmosis and thermal distillation are two widely used methods for desalination.
- Describe the disadvantages of using desalination for the production of potable water.
Video: Desalination (Flippin' Science)
Virtual Tour (Sydney plant)
Hypochlorous acid, chlorine, and hypochlorites are oxidisers used for water disinfection.
- Explain the effect of pH on the equilibrium between chlorine and water, and hydrochloric acid and hypochlorous acid.