Page 68 - ICSE Chemistry 6

Activity 3.14

Aim: To show expansion of gas on hea ng
Materials required: A tumbler, coloured water, capillary tube, cork, test tube, burner

Procedure
• Take a tumbler and fi ll it with some coloured water.
• Take a capillary tube and dip its one end in the coloured water. Take a drop of coloured water in the
capillary tube.
• Fix the capillary through a hole in the cork and carefully fi t the cork in a test tube.
• Now heat the test tube.

Observa on: You will observe that the drop of water rises up.
Conclusion: This shows that the air in the test tube expands on hea ng and causes the drop of water to
rise.
On cooling the test tube, the water drop comes down which shows that air contracts on cooling.

The internal diameter of a capillary tube is very thin.

Chemical Change on Heating

A chemical change is a change in which new substances are formed. It is a permanent change. The
proper es of newly formed substances are en rely diff erent from those of the original substances.

A chemical change can be caused by hea ng a substance. For example, when we burn a piece of paper,
it changes into ash which is a new substance. The proper es of ash are diff erent from those of the paper.
We cannot change ash to paper. This shows that burning of paper causes a chemical change.
Similarly, burning of a candle is also a chemical change. When we heat a candle, candle wax melts and
then changes into vapour. This vapour reacts with air and forms two new substances including carbon
dioxide and water vapour.
Burning of a candle Candle wax Carbon dioxide + Water vapour

Hence, we observe that the candle becomes smaller and smaller on burning, and the recovery of the part
of wax which has undergone chemical change cannot take place.

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