Question

A metal obtained directly by roasting of its sulphide ore is
(A) $Cu$
(B) $Pb$
(C) $Hg$
(D) $Zn$

Answer 1

Hint: In the metallurgical process of roasting, ore is heated below its melting point in the presence of excess air and converted into its oxide. Roasting is an exothermic process. Roasting is carried out to ensure that the desired chemical reaction begins slowly, continues for a sufficient amount of time to transform enough of the product's chemicals into the desirable material, and then ends. Roasting is an exothermic process.

Complete Step by Step Answer:
Volatile substances, moisture, and impurities are all eliminated throughout the process of roasting. There is no dehydration step in the roasting process. The mercury sulphide ($HgS$) can be converted into its oxide by the process of roasting at a temperature of 773 K to 873 K.

Mercury starts to vaporise at this temperature, and the vapours eventually condense into the liquid metal.
$HgS + O_2\overset{773-873K}{\rightarrow} Hg + SO_2$
The mercury obtained by this method is about 99.7% pure. From the given options, the metal obtained directly by roasting of its sulphide ore is$Hg$.
Correct Option: (C) $Hg$.

Additional Information: The process of roasting has many advantages. The substances that have been roasted can easily be powdered. It is a very quick method and requires very little fat. The content of moisture in the substances that have been roasted, gets reduced.

Note: Sulphide-based roasting is a major source of air pollution, and it has the further disadvantage of releasing great amounts of acidic, poisonous, and metallic chemicals into the environment.