unit 2.3 Flashcards
What does natural water contain?
- Dissolved ions
- Dissolved gases
- Microorganisms
- Pollutants
What is sedimentation?
- First stage of water treatment
- Large insoluble particles settle at the bottom of the sedimentation tank.
- Clean water from the top is extracted for the next stage.
What is filtration?
- Second stage of water treatment
- A filter of sand, gravel and charcoal removes smaller insoluble particles.
What is chlorination?
- Third stage of water treatment
- Small amounts of chlorine are added to water to kill any harmful bacteria and microorganisms.
What is demineralisation (tooth decay) ?
When the enamel on the outer surface of our teeth reacts with acid and dissolved.
What is remineralisation?
When the acids are neutralised by saliva etc.
What are the benefits of flourination?
- Prevents tooth decay in young children by making their enamel resistant to reacting with acid.
- Kills bacteria
- Stronger teeth
What are disadvantages to flourination?
- Can cause dental flourosis
- Can cause stomach/ bone cancer and infertility
- Seen as a form of mass medication
What is desalination?
The removal of salt from sea water.
How does reverse osmosis desalination work?
Seawater is forced through a semi-permeable membrane at a high pressure. The membrane allows water molecules to pass through but not salt.
How does thermal desalination work?
Sea water is heated so the water evaporates. Water vapour is collected and condensed and the salt is used for other purposes.
What are the characteristics of temporary hard water?
- Contains calcium or magnesium hydrogen carbonate.
- Can be softened by boiling but it can leave scale behind.
What are the characteristics of permanent hard water?
- Contains compounds containing Calcium or Magnesium.
- Can’t be softened by boiling.
- reacts with soap to form scum.
How can you remove water hardness?
- By adding sodium carbonate
- Boiling (temporary only)
- Ion exchange
How does ion exchange remove hard water?
Ion exchange collumns contain hydrogen or sodium ions. These replace the calcium and magnesium ions when water passes through the collumn.
