General Principles and Processes of Isolation of Elements — Chemistry STD 12 Science — Question
Gujarat BoardEnglish MediumSTD 12 ScienceChemistryGeneral Principles and Processes of Isolation of Elements2 Marks
Question
Giving examples, differentiate between 'roasting' and 'calcination'.
✓
Answer
Roasting is the process of converting sulphide ores to oxides by heating the ores in a regular supply of air at a temperature below the melting point of the metal. For example, sulphide ores of Zn, Pb, and Cu are converted to their respective oxides by this process.
$2\text{ZnS}+3\text{O}_2\xrightarrow[]{\ \ \Delta\ \ }2\text{ZnO}+2\text{SO}_2\\\text{Zinc blende}$
$2\text{Pbs}+3\text{O}_2\xrightarrow[]{\ \ \Delta\ \ }2\text{PbO}+2\text{SO}_2\\\text{Gelena}$
$2\text{Cu}_2\text{S}+3\text{O}_2\xrightarrow[]{\ \ \Delta\ \ }2\text{Cu}_2\text{O}+2\text{SO}_2\\\text{Copper glance}$
On the other hand, calcination is the process of converting hydroxide and carbonate ores to oxides by heating the ores either in the absence or in a limited supply of air at a temperature below the melting point of the metal. This process causes the escaping of volatile matter leaving behind the metal oxide. For example, hydroxide of Fe, carbonates of Zn, Ca, Mg are converted to their respective oxides by this process.
$\text{Fe}_2\text{O}_3.3\text{H}_2\text{O}\xrightarrow[]{\ \ \Delta\ \ }\text{Fe}_2\text{O}_3+3\text{H}_2\text{O}\\\ \ \text{Limonite}$
$\text{ZnCO}_{3(\text{s})}\xrightarrow[]{\ \ \Delta\ \ }\text{ZnO}_{(\text{s})}+\text{CO}_{2(\text{g})}\\\ \ \text{Calamine}$
$\text{CaMg}(\text{CO}_3)_2\xrightarrow[]{\ \ \Delta\ \ }\text{CaO}_{(\text{s})}+\text{MgO}_{(\text{s})}+2\text{CO}\\\ \ \text{Dolomite}$
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