Question

Bubbles are seen in the test tube during the preparation of lime water.

Answer 1

Lime water is a saturated solution of calcium hydroxide (Ca(OH)2). It is commonly prepared by passing carbon dioxide gas through a solution containing quicklime (CaO) or slaked lime (Ca(OH)₂) in water.

1. Formation of Lime Water: \[\ce{CaO + H2O -> Ca(OH)2}\]
   Quicklime reacts with water to form slaked lime (calcium hydroxide), which dissolves slightly in water to form lime water.
2. Bubbling of CO₂ (Observation of Bubbles): \[\ce{Ca(OH)2 + CO2 -> CaCO3 ↓ + H2O}\]
   

   • When CO₂ gas is passed through the lime water, it reacts with the calcium hydroxide.

   • The bubbles observed are CO₂ gas bubbles.
   • The reaction produces calcium carbonate, which causes the solution to turn milky.