NIOS Class 10 Science Activity 26.1 Air and Water | Complete Explanation

In this activity, we will prove the presence of carbon dioxide in the air through a simple experiment.

Air and Water Activity Solution

This activity is based on the NIOS Class 10 science and technology (212) Chapter 26- Air and Water Module 6- Natural Resources.

Aim

To show the presence of CO₂ in air

Materials Required

   1.  Test tube or glass tumbler

   2. Fresh lime water

   3. Cork with two holes

   4. Two glass tubes or straw pipes

   5. Vaseline

Procedure

We take about 4 mL of freshly prepared lime water in a test tube or glass tumbler. Then we fix a cork (with two holes in it) on its mouth.

Now we insert two straw pipes (bent at right angles) through holes in the tube – one dipping in the lime water and the other remaining above the liquid and apply Vaseline around them to make them air-tight.

Then we suck the air through the tube that is not dipped in the lime water and observe what happens.

Observation 

 We see air bubbles in the lime water, and it turns milky after a short time.

Explanation

When we suck the air from the tube, the air pressure inside the tube decreases, and atmospheric air enters the tube through the straw dipped in the lime water.

 The lime water turns milky because the carbon dioxide gas present in the air reacts with calcium hydroxide and forms calcium carbonate, which is insoluble and white.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Conclusion

 This activity proves that carbon dioxide present in the air and its small concentration turns lime water milky.

Frequently Asked Questions

   1. What happens when lime water reacts with CO₂?

Ans – Lime water turns milky because of the formation of calcium carbonate.

   2. Why do we use freshly prepared lime water?

Answer – Because old lime water loses its reactivity.

   3. How is lime water prepared?

Answer – Lime water is prepared by adding water to calcium oxide (quick lime or chuna). Fresh lime water is hot, so it is kept for some time undisturbed.

   4. Can lime water become clear again?

Answer – Yes, if excess CO₂ is passed in the solution, calcium carbonate is dissolved to form calcium bicarbonate and the solution becomes clear again.