Question

Which metal is obtained by self reduction process?
A.Cu
B.Pb
C.Hg
D.All of these

Answer 1

Hint: The naturally occurring chemical substances in the form of which the metals occur in the earth along with some impurities are referred to as minerals. On the other hand, the minerals from which the metal is extracted conveniently and economically are referred to as ores. Thus, it can be concluded that all the ores are minerals but all the minerals are not ores.
The process of extracting the metals from their respective ores is termed as ‘metallurgy’. The process which is used to obtain metals in their free state from their concentrated ores is termed as ‘extraction’.

Complete step by step answer:
-Many metals can be easily obtained from their respective oxides by reduction and so, the extraction of metals the following two chemical processes:
-The conversion of the ore into its corresponding metal oxide
-The reduction of the metal oxide to the corresponding free metal.
-Many metals are usually present in ores as oxides, sulphides and carbonates. Depending upon the type of minerals present in the ores, the two methods of calcination and roasting are generally used for converting ores into their respective oxides. Calcination involves heating of ore in absence or limited supply of air while roasting involves heating of ore in presence of air.
-After this, the roasted or calcined ore is reduced to the metal by the help of a suitable reducing agent. This is called pyrometallurgy.
-In some cases, there is no need for suitable reducing agents and then the process is called auto reduction or self-reduction. In self reduction, the sulphide ores of less electropositive metals are heated in air so as to convert a part of the ore into oxide or sulphate which then reacts with the remaining part of the sulphide ore in absence of air to give the metal and sulphur dioxide. It is referred to as self reduction as no external reducing agents are used.
-Copper, lead and mercury are all less electropositive metals and so they can be extracted by self-reduction from their respective sulphide ores.
-In the extraction of copper from its sulphide ore, the ore is subjected to partial roasting in air to form its oxide.
${\text{2C}}{{\text{u}}_{\text{2}}}{\text{S + 3}}{{\text{O}}_{\text{2}}} \to {\text{2C}}{{\text{u}}_2}{\text{O + 2S}}{{\text{O}}_{\text{2}}}$
-After the air supply is stopped, the rest of the sulphide ore reacts with the oxide to form the metal.
${\text{C}}{{\text{u}}_{\text{2}}}{\text{S + 2C}}{{\text{u}}_2}{\text{O}} \to 6{\text{Cu + S}}{{\text{O}}_{\text{2}}}$
The same explanation can be given for the extraction of mercury and lead too.
For mercury,
$
  {\text{2HgS + 3}}{{\text{O}}_{\text{2}}} \to 2{\text{HgO + 2S}}{{\text{O}}_{\text{2}}} \\
  {\text{2HgO + HgS}} \to {\text{3Hg + S}}{{\text{O}}_{\text{2}}} \\
 $
And for lead,
$
  {\text{2PbS + 3}}{{\text{O}}_{\text{2}}} \to 2{\text{PbO + 2S}}{{\text{O}}_{\text{2}}} \\
  {\text{2PbO + HgS}} \to {\text{3Pb + S}}{{\text{O}}_{\text{2}}} \\
 $
Therefore, all the options are correct.

Hence the correct option is D.

Note:
-The choice of reducing agent for reduction through reducing agents depends upon the reactivity of the metal.
-If the metal to be extracted is very reactive like the alkali metals or the alkaline earth metals, then the reduction of the oxide is done only by the electrolytic method.
-If the metal to be extracted is less reactive like zinc, iron, copper, tin, manganese etc., then their oxides are reduced by a number of reducing agents like carbon or coke, carbon monoxide etc.