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Science · 2023 · 3 marks
CBSE 2023 · Region 2 · Set 1 · Q28
With the help of suitable chemical equations, list the two main differences between roasting and calcination. How is metal reduced from the product…
With the help of suitable chemical equations, list the two main differences between roasting and calcination. How is metal reduced from the product obtained after roasting/calcination of the ore ? Write the chemical equation for the reaction involved.
Marking-scheme solution
| Roasting | Calcination | |
| $\displaystyle 1$ | It is carried out for sulphide ores. | It is carried out for carbonate ores. |
| $\displaystyle 2$ | Ore is heated in excess of air \[ 2 \mathrm{ZnS}+3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{ZnO}+2 \mathrm{SO}_{2} \] OR \[ 2 \mathrm{HgS}+3 \mathrm{O}_{2} \xrightarrow{\text { Heat }} 2 \mathrm{HgO}+2 \mathrm{SO}_{2} \] OR \[ 2 \mathrm{Cu}_{2} \mathrm{~S}+3 \mathrm{O}_{2} \xrightarrow{\text { Heat }} 2 \mathrm{Cu}_{2} \mathrm{O}+2 \mathrm{SO}_{2} \] | Ore is heated in absence or limited supply of air. \[ \mathrm{ZnCO}_{3} \xrightarrow{\text { Heat }} \mathrm{ZnO}+\mathrm{CO}_{2} \] OR \[ \mathrm{CaCO}_{3} \xrightarrow{\text { heat }} \mathrm{CaO}+\mathrm{CO}_{2} \] OR \[ \mathrm{PbCO}_{3} \xrightarrow{\text { heat }} \mathrm{PbO}+\mathrm{CO}_{2} \] |
Reduction with the help of carbon
\[\mathrm{ZnO}+\mathrm{C} \underset{\text { Heat }}{\longrightarrow} \mathrm{Zn}+\mathrm{CO}
\]
Alternate answer
With the help of heat
\[2 \mathrm{HgO}(\mathrm{~s}) \xrightarrow{\text { Heat }} 2 \mathrm{Hg}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})
\]
OR
Auto reduction / Heating with its ore
\[2 \mathrm{Cu}_{2} \mathrm{O}+\mathrm{Cu}_{2} \mathrm{~S} \xrightarrow{\text { Heat }} 6 \mathrm{Cu}(\mathrm{~s})+\mathrm{SO}_{2}(\mathrm{~g})
\]
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