Question

Cupellation is used for purification of:
(A)- Pb
(B)-Ag
(C)-Zn
(D)-Fe

Answer 1

Hint: Cupellation is a refining process.it is used when ores or metals are present under high temperature. The noble metals are separated from impurities using a cupel which is a flat, porous dish.
It is also used for coin making and testing fresh metals.

Complete answer:
-Cupellation works on principle that noble metals do not undergo oxidation and they are chemically unreactive.
-when noble metals are exposed to high temperatures, they remain unaffected and other impurities, metals etc. reacts to form slag or other compounds.
-In large scale cupellation,
Native silver is found rarely, and silver is usually associated with lead sulphide or lead carbonate.
-smelting is used to separate silver from lead.
-smelting is applying heat to ore in order to extract metal.
As lead metals at around 300 degree Celsius and silver metals at around 950 degree Celsius, to separate silver, alloy is melted at high temperature in an oxidizing environment.
Lead monoxide is produced due to oxidation of lead and is removed.
In small scale cupellation,
Cupel is used which is an inverted cone shape.
Cupel is heat resistant, flat porous dish then blast of air is directed.
Impurities like lead, copper and other unwanted metals undergo oxidation, they are vaporized or absorbed in pores of cupel.

So, cupellation process is used in purification of option (B)

Note: Small scale cupellation is used in assaying. The size of cupel depends upon the amount of material to be assayed. Miller and Wohlwill processes are used in purification of gold. In miller process,
Gaseous chlorine is used to extract impurities when gold reaches its melting point.