Question

It is observed that Calcium on reaction with water floats on its surface. Explain why it happens. Also write a balanced chemical equation for the reaction that occurs. What happens when the aqueous solution of the product of this reaction reacts with Carbon dioxide gas? Write a balanced chemical equation for the reaction.

Answer 1

Step 1: Reaction of Calcium with Water
When calcium (Ca), a metal, is added to water (H₂O), it reacts slowly to form calcium hydroxide [Ca(OH)₂] and hydrogen gas (H₂).

Balanced Chemical Equation:
Ca (s) + 2H₂O (l) → Ca(OH)₂ (aq) + H₂ (g)

Step 2: Why Calcium Floats
During this reaction, hydrogen gas is released. The gas forms bubbles that stick to the surface of the calcium metal.
- These bubbles make calcium less dense in water.
- As a result, calcium begins to float on the water surface.

Step 3: Reaction of Calcium Hydroxide with Carbon Dioxide
The calcium hydroxide formed dissolves in water to create a basic solution known as limewater.
When carbon dioxide (CO₂) gas is passed through this solution, it reacts to form calcium carbonate (CaCO₃), a white solid that appears as a precipitate.

Balanced Chemical Equation:
Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l)

Step 4: Observation
- Calcium floats on water with effervescence (due to hydrogen gas).
- A white precipitate forms when CO₂ is passed through the calcium hydroxide solution.

Conclusion:
Calcium reacts with water to form calcium hydroxide and hydrogen gas. The gas bubbles cause calcium to float. Calcium hydroxide then reacts with carbon dioxide to form a white precipitate of calcium carbonate.