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Science · 2023 · 4 marks
CBSE 2023 · Region 6 · Set 1 · Q37
On the basis of reactivity metals are grouped into three categories - (i) Metals of low reactivity (ii) Metals of medium reactivity (iii) Metals of…
On the basis of reactivity metals are grouped into three categories -
(i)
Metals of low reactivity
(ii)
Metals of medium reactivity
(iii)
Metals of high reactivity Therefore metals are extracted in pure form from their ores on the basis of their chemical properties. Metals of high reactivity are extracted from their ores by electrolysis of the molten ore. Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.
(a)
Name the process of reduction used for a metal that gives vigorous reaction with air and water both.
(b)
Carbon cannot be used as a reducing agent to obtain aluminium from its oxide ? Why ?
(c)
Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reactions involved in the process.
OR
(c)
Differentiate between roasting and calcination giving chemical equation for each.
Marking-scheme solution
(a) By electrolytic reduction
(b) Carbon cannot reduce the oxides of highly reactive metals / these metals have more affinity for oxygen than carbon.
(c) When Cinnabar is heated in the presence of air, it is first converted into mercuric oxide. / This is then reduced to mercury.
\[\begin{aligned}
& 2 \mathrm{HgS}+3 \mathrm{O}_{2} \xrightarrow{\text { heat }} 2 \mathrm{HgO}+2 \mathrm{SO}_{2} \\
& 2 \mathrm{HgO} \xrightarrow{\text { heat }} 2 \mathrm{Hg}+\mathrm{O}_{2}
\end{aligned}
\]
| Roasting | Calcination |
| A process in which sulphide ores are converted into oxides by heating strongly in the presence of excess air \[ \begin{aligned} & 2 \mathrm{ZnS}+3 \mathrm{O}_{2} \xrightarrow{\text { heat }} 2 \mathrm{ZnO}+ \\ & 2 \mathrm{SO}_{2} \end{aligned} \] | A process in which carbonate ores are heated in limited supply air. \[ \begin{aligned} & \mathrm{ZnCO}_{3} \xrightarrow{\text { heat }} \mathrm{ZnO}+ \\ & \mathrm{CO}_{2} \end{aligned} \] |
| (or any other) |
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