Q1.
Put a teaspoon of sugar in a boiling tube. Heat it gently as shown in Fig. 8.12a. What do you observe?
Answer
The sugar changes in three clear stages.
- It melts and turns brown (Fig. 8.12b).
- On further heating it begins to char — it turns blackish (Fig. 8.12c).
- Small droplets of water appear inside the boiling tube near its open end, and a black solid, charcoal (carbon), is left behind.
Sugar (on heating) → Carbon + Water
Why it happens: Sugar decomposes on heating. The water and the black charcoal did not exist in the tube before, so a new set of substances has been formed — this is a chemical change, and it is the proof that sugar is made of more than one element.
Safety first: This activity must be performed in the presence of a teacher. Hold the boiling tube with a test tube holder and keep its mouth pointed away from everyone.