Cloudy Lime Water Test
React CO2 with calcium hydroxide to form precipitate
What this lesson covers
Why it matters
Breathe into a glass of clear lime water and watch it turn opaque white. The invisible gas has left a solid fingerprint.
The idea in plain words
Map the reactants to products: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. Note the state change of the calcium compound.
Predict first
Why does clear lime water turn milky when carbon dioxide is passed through it?
The CO2 reacts with dissolved calcium hydroxide to form calcium carbonate, which is insoluble in water and appears as a white precipitate.
- The water boils and creates bubbles
- An insoluble white solid, calcium carbonate, forms — correct
- The calcium hydroxide dissolves completely
- The CO2 turns into liquid water instantly
What you do
Bubble CO2 into the lime water. Observe the formation of the white precipitate.
Check yourself
What is the chemical formula of the white precipitate formed?
The reaction produces calcium carbonate (CaCO₃), which is insoluble and causes the milky appearance.
Which observation confirms the presence of carbon dioxide?
The specific test for CO2 is the formation of a white precipitate (CaCO3) in lime water.
What is the other product formed in this reaction besides the precipitate?
The balanced equation Ca(OH)₂ + CO₂ → CaCO₃ + H₂O shows water is the second product.
- Ca(OH)₂
- CaCO₃ — correct
- CaO
- Ca(HCO₃)₂
- The solution turns blue
- A white precipitate forms — correct
- The solution becomes hot
- Bubbles of oxygen gas are released
- Oxygen gas
- Water — correct
- Hydrogen gas
- Carbon monoxide