Boil Away Hardness
Remove temporary hardness by boiling
What this lesson covers
Why it matters
Boil water from a temporary hard source and watch a white precipitate settle at the bottom. This precipitate is the key to softening the water.
The idea in plain words
Read the equation: one Ca(HCO₃)₂ splits into three products on boiling — the insoluble CaCO₃ is the kettle fur.
Predict first
What happens to calcium bicarbonate when you boil the water?
Heat triggers thermal decomposition, breaking down the soluble bicarbonate into an insoluble solid.
- It evaporates completely with the water
- It decomposes into insoluble calcium carbonate, water, and carbon dioxide — correct
- It remains unchanged because it is stable
What you do
Apply heat to the solution. Observe the formation of the white precipitate and the release of gas.
Check yourself
Why does boiling remove temporary hardness?
The white precipitate of CaCO₃ can be filtered out or settled, leaving softer water.
What is the white solid formed during this process?
The equation shows CaCO₃ as the solid product, often seen as fur in kettles.
Which gas is released during the decomposition?
The reaction produces CO₂ gas along with water and calcium carbonate.
- It kills bacteria in the water
- It converts soluble calcium bicarbonate into insoluble calcium carbonate — correct
- It adds more calcium to the water
- Calcium bicarbonate
- Calcium carbonate — correct
- Calcium oxide
- Oxygen
- Carbon dioxide — correct
- Hydrogen