Chemistry- Water

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  • Created by: Chesca
  • Created on: 15-05-13 17:01

Hard & Soft Water

Soft Water = easily forms thick, rich lather with soap (no dissolved substances)

Hard Water = doesn't easily form lather with soap

  • contains calcium and magnesium ions
  • Calcium & magnesium + soap = SCUM!

Hard water forms...:

  • Ca+ Mg ions dissolve in water when pass over rocks containing them
  • Rock = limestone (calcium carbonate/insoluable in water)
  • Rain falls...CO2 dissolves in it, makes water acidic
  • Calcium carbonate reacts with acid - forms calcium hydrogencarbonate
  • Soluable in water....Ca ions get into water :)
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Hard Water and soap + heating

Calcium + magnesium ions react with water to form SCUM!

  • Only once all ions have reacted that lather forms

Hard water leads to SCALE (limescale) forming

  • Formed as insoluable soild, when heat a type of water.
  • Formed in washing machines, pipes and kettles
  • Scale in kettle's (furring up) in heating element, makes kettle inefficient
  • Scale = poor conductor of energy - costs more energy to heat water.


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Advantages of Hard Water

  • Calcium ions develop strong bones and teeth
  • Hard water reduces heart disease

Advantages of softening hard water:

  • Doesn't waste soap
  • No scum or scale is formed when heating
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Temporary and permanent hardness

Temporary hard water: water that can have it's hardness removed by boiling

Permanently hard water: water that remains hard after boiling.

Heating temporarily hard water:

  • When boil water containing hydrogencarbonate ions they decompose!
  • Carbonate ions react with Ca+ or Mg+ ions in hard water - removes them, softens water!
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Softening hard water

Washing Soda (sodium carbonate):

  • Add sodium carbonate
  • Soluable carbonate ions precipitate out calcium and magnesium ions.
  • Dissolved metal ions form insoluable carbonates!

Ion Exchange column:

  • Removes Ca+ and Mg+ ions
  • Column contains resin packed with sodium ions
  • Hard water passes through column
  • Sodium ions exchanged for calcium and magnesium ions
  • Wash resin with salt solution to put sodium ions back in.
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Water treatment

As water enters...passes through METAL SCREEN to catch large objects

Settlement tank = sand and soil settled

Aliuminium sulfate and lime added- clump particles together

Passed through filter of fine sand to remove remaining particles

CHLORINE added to kill off bacteria

pH of water checked = water pumped to schools, factories etc...

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Further Water Treatment

Water from boreholes clean = filtered through rocks

Water jugs: water enters, passes through filter cartridge

  • contains carbon (reduces levels of chlorine, pesticides)
  • Ion exchange resin removes calcium, magnesium and lead ions
  • Silver = discourages growth of bacteria


Can get 'pure water' by distilling it!

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Water issues

Chlorine....= can react with organic molecules and form toxic products.

  • using 'ozone' is an alternative

Fluoride = added to protect teeth from decay

  • For flurodiation: been in water for years no harmful effects, reduces cavities in teeth, only added in tiny amount
  • Against flurodiation: Flurosis= too much fluoride - can weaken bones cause marks on teeth, ethically wrong to give something with no consent, may affect brain.
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