Question

Refining of silver is done by

• A. Polling
• B. Van arkel method
• C. liquation
• D. cupellation

Answer 1

The correct option is D

cupellation

The explanation for the correct option:

Option (D): Cupellation

1. It is a metallurgical process in which ores or alloyed metals are heated to a high temperature and then subjected to specific procedures to separate noble metals like gold and silver from base metals like lead, copper, zinc, and other elements contained in the ore.
2. The method is based on the fact that, unlike base metals, precious metals do not react chemically.
3. The precious metals remain separate when heated to high temperatures, while the others react, generating slags or other compounds.
4. Pure silver is a rare element that does exist. It is frequently found in nature as a mixture of metals or in minerals containing silver compounds, such as lead sulfide or lead carbonate.
5. Smelting and cupellation of silver containing lead ores are thus required for the primary production of silver.
6. Lead oxidizes to lead monoxide, then litharge, which absorbs oxygen from the surrounding metals. Capillary action removes the liquid lead oxide from the hearth linings. $\underset{\mathrm{Silver}}{\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{Lead}}{2\mathrm{Pb}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}\mathrm{gas}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Lead}\mathrm{oxide}\left(\mathrm{Absorbed}\right)}{2\mathrm{PbO}\left(\mathrm{s}\right)}+\underset{\mathrm{Silver}}{\mathrm{Ag}\left(\mathrm{s}\right)}$

The explanation for incorrect options:

Option (A): Polling

1. This is a method of purifying metals that contain their own oxide as an impurity.
2. It is commonly used to remove metal oxide impurities such as copper oxide ${\mathrm{CuO}}_2$or tin oxide ${\mathrm{SnO}}_2$
3. We employ two procedures to remove oxide impurities: first, oxidation, and subsequently reduction.

Option (B): Van Arkel method:

1. It is possible to obtain very pure metal with this method.
2. The impure metal is transformed into a volatile chemical, which is subsequently thermally decomposed to yield metal.
3. This process purifies Zirconium, Titanium, Hafnium, and Silicon.

Option (C): liquation

1. Flammable metals like lead and tin are refined using liquation. The impure metal is heated in an electric furnace's sloping hearth. Impurities are left behind as the metal melts and flows down.
2. Differences in melting temperatures and densities of alloy constituents, as well as the low level of mutual solubility of the constituents, are used to separate liquids.

Therefore, the refining of silver is done by option (D) cupellation.