Write balanced chemical equations to explain what happens, when (i) Mercuric oxide is heated. (ii) Mixture of cuprous oxide and cuprous sulphide is heated

Question: Write balanced chemical equations to explain what happens, when

(i) Mercuric oxide is heated.

(ii) Mixture of cuprous oxide and cuprous sulphide is heated.

(iii) Aluminium is reacted with manganese dioxide.

(iv) Ferric oxide is reduced with aluminium.

(v) Zinc carbonate undergoes calcination. [CBSE OD, Set 1, 2020]

Answer: (i) Cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.

 2HgO(s)  + Heat→ 2Hg(l) + O₂(g)

(ii) When a mixture of copper oxide and copper sulphide is heated metallic copper is formed along with the evolution of the sulphur dioxide gas. The reaction equation is as follows:

 2Cu₂O + Cu₂S → 6Cu + SO₂

(iii) When aluminium powder is reacted with manganese dioxide, Manganese and aluminium oxide are formed with the evolution of heat and the following reaction takes place:

3MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + Heat

(iv) When ferric oxide is reduced with aluminium a displacement reaction takes place and this reaction is highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. In fact, the reaction of iron (III) oxide (Fe₂O₃) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermite reaction.

Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat

(v) The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during calcination of zinc ores can be shown as follows:

ZnCO3(s) + Heat →  ZnO(s) + CO2(g)