CBSE Class 10 Science 2020 · Paper 31/3/1 · Question 25(a)

Metals and Non-metals 5 marks Medium

Write balanced chemical equations to explain what happens, when

Answer

HgO gives mercury, $Cu_{2} O$ with $Cu_{2} S$ gives copper, Al displaces Mn and Fe from their oxides, and $ZnCO_{3}$ gives ZnO.

(i) Mercuric oxide decomposes into mercury and oxygen:

2 HgO (s) heat 2 Hg (l) + O_{2} (g)

(ii) The mixture reacts to give copper and sulphur dioxide (self-reduction):

2 Cu_{2} O + Cu_{2} S heat 6 Cu + SO_{2}

(iii) Aluminium displaces manganese, with the release of a lot of heat:

3 MnO_{2} (s) + 4 Al (s) ⟶ 3 Mn (l) + 2 Al_{2} O_{3} (s) + heat

(iv) Aluminium displaces iron (thermit reaction), giving molten iron:

Fe_{2} O_{3} (s) + 2 Al (s) ⟶ 2 Fe (l) + Al_{2} O_{3} (s) + heat

(v) Zinc carbonate is converted into zinc oxide and carbon dioxide:

ZnCO_{3} (s) heat ZnO (s) + CO_{2} (g)

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