Hard Water

Revision cards on Hard Water topic for CCEA - GCSE level

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Hard Water

  • Hard Water does not form a lather easily with soap.
  • Hard Water is caused by Calcium or Magnesium ions dissolved in water.
  • Ca2+ or Mg2+ react with stearate ions of soap to form calcium or magnesium stearate - commonly called scum.
  • 2 types of hard water - temporary and permanent
  • Temporary can be softened by boiling permanent cannot.
  • Temporary hard water is caused by rainwater with dissolved CO2 in it falling on limestone.
  • This produces the soluble compound Calcium Hydrogen Carbonate - leaving Ca2+ dissolved in water.
  • Calcium Carbonate + Water + Carbon Dioxide = Calcium Hydrogen Carbonate
  • CaCO3 + H2O + CO2 = Ca(HCO3)2
  • Permanent Hard Water is caused by calcium or magnesium sulphate dissolved in water.
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Softening Hard Water

Boiling

  • Temporary Hard Water can be softened by boiling it, Permanent cannot!!
  • Temp. HW is caused by the compound Calcium Hydrogen Carbonate (Ca(HCO3)2)
  • When boiled Ca(HCO3)2 decomposes to form Calcium Carbonate, Water and Carbon Dioxide.
  • Ca(HCO3)2 = CaCO3 + H2O + CO2
  • CaCO3 is insoluble, so Ca2+ are precipitated, water is now soft.

Adding Washing Soda (Sodium Carbonate)

  • Can be used to soften both types of HW
  • Ca2+ react with CO32- to form CaCO3

Temporary

  • Calcium Hydrogen Carbonate + Sodium Carbonate = Calcium Carbonate + Sodium Hydrogen Carbonate
  • Ca(HCO3)2 + Na2CO3 = CaCO3 + 2NaHCO3
  • CaCO3 is insoluble, so Ca2+ are precipitated, water is now soft.

Permanent

  • Calcium Sulphate + Sodium Carbonate = Calcium Carbonate + Sodium Sulphate
  • CaSO4 + Na2CO3 = CaCO3 + Na2SO4
  • CaCO3 is insoluble, so Ca2+ are precipitated, water is now soft.

Ion Exchange Column

  • HW is poured into top of column
  • In column there are Na+ stuck on a resin
  • Ca2+ in HW swap places with Na+ - They stick to resin and Na+ go in water
  • Na+ do not cause hardness 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Advantages and Disadvantages of Hard Water

Advantages

  • Contains Ca2+ so good for teeth and bones
  • Tastes Nicer
  • Used to brew beer
  • Used in tanning of leather
  • Ca2+ help prevent heart disease

Disadvantages

  • Wastes soap
  • Costs money to soften
  • Boiling Temp HW causes the build up of limescale in kettles, boilers, pipes etc..
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