Water Treatment (Cambridge O Level Chemistry)

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Alexandra Brennan

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Water Treatment

Water supply

  • Water is taken from rivers, reservoirs or underground water sources (groundwater)
  • A rock that stores water is known as an aquifer

Water treatment

  • Untreated water contains soluble and insoluble impurities
  • Insoluble impurities include soil, pieces of plants and other organic matter
  • Soluble impurities include dissolved calcium, metallic compounds and inorganic pollutants
  • Water is pumped into sedimentation tanks where the water is allowed to stand for a few hours
  • Mud, sand and other particles will fall to the bottom of the tank due to gravity and form a layer of sediment, in a process called sedimentation
  • Filtration is the process used to remove smaller particles by passing the water through layers of sand and gravel filters that trap solid particles
  • Water can also be passed through carbon (in the form of charcoal) to remove tastes and odours
  • Bacteria and other microorganisms are too small to be trapped by the filters so chlorination is used
  • This involves the careful addition of chlorine to the water supply which kills bacteria and other unwanted microorganisms
  • Cholera and typhoid are examples of bacterial diseases which can arise from the consumption of untreated water

 

10-1-3-water-treatment

Diagram showing the stages in the treatment of water

Examiner Tip

Exam questions on water treatment often focus on the purpose of each stage of the process.

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.