CBSE Class 10 Science 2019 · Paper 31/3/1 · Question 7(b)

Ore of mercury: cinnabar, mercury(II) sulphide ($\text{HgS}$). Extraction: Mercury is low in the activity series, so it is obtained from its ore by heating alone. 1. Roasting: Cinnabar is heated strongly in the presence of excess air. It is converted into mercuric oxide, and sulphur dioxide is given off: $2\text{HgS}(\text{s})+3{\text{O}}_2(\text{g})\stackrel{\text{heat}}{\to }2\text{HgO}(\text{s})+2{\text{SO}}_2(\text{g})$ 2. Reduction by heating: The mercuric oxide is then heated further. It decomposes to give mercury (a liquid) and oxygen: $2\text{HgO}(\text{s})\stackrel{\text{heat}}{\to }2\text{Hg}(\text{l})+{\text{O}}_2(\text{g})$