Temporary hard water can be softened by heating:
- Temporary hard water contains hydrogen carbonate ions
- They decompose when heated to produce carbonate ions, water and carbon doixide
- 2HCO3 - = CO3 2- + CO2 + H2O
- The carbonate ions react with the magnesium and calcium ions
- They produce solid precipitates of Ca or Mg carbonates - deposited as scale
- Ca 2+(aq) + CO3 2-(aq) = CaCO3(s)
Washing soda
- Washing soda contains sodium carbonate and is mixed with the water
- The calcium and magnesium ions react with the sodium carbonate
- Produces solid precipitates of Ca/Mg carbonates which can be filtered from water
- Sodium remains in the water
Ion exchange collumn
- Collumn packed with resin containing sodium or hydrogen ions
- As water passes through, Ca and Mg ions attach to resin
- Sodium / hydrogen ions replace the Mg or Ca ions in the water
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