Answer the following:
Raj is given a mixture of Ammonium chloride and common salt. To separate the components, the student sets up the apparatus shown below. The mixture is placed in a china dish and heated gently. An inverted funnel is placed over the dish, and the stem of the funnel is plugged with cotton.
1. Which substance changes directly from solid to vapour during heating?
2. Where will the ammonium chloride be collected after heating?
3. Why is the stem of the funnel plugged with cotton?