Question

Identify M and N in the following reaction.
$
  Copper\_glance\xrightarrow{{controlled\_heating\_in\_presence\_of\_air}}M + S{O_2} \uparrow \\
  M\xrightarrow{N}Cu + S{O_2} \uparrow \\
$
A. $M = C{u_2}O$; N= self reduction
B. $M = C{u_2}O + C{u_2}S$; N= self reduction
C. $M = C{u_2}O$; N= carbon reduction
D. $M = C{u_2}O$; N= electrolytic reduction

Answer 1

Hint: Copper glance is heated in the presence of air, so the products must be Copper compounds. And these copper compounds are further reacted to formed Copper metal and Sulphur dioxide. Here the products have sulphur therefore, the reactants must also have sulphur. Find the option with sulphur present in it and that will be our answer.

Complete step by step solution:
We are given to find the missing compounds in the given reactions and the reaction type.
Copper glance is also known as cuprous sulphide whose chemical formula is $C{u_2}S$.
Copper glance is initially heated in the presence of air (oxygen) to form Cuprous oxide and Sulphur dioxide and also leaving a little copper glance behind.
$3C{u_2}S + 3{O_2}\xrightarrow{{controlled}}C{u_2}S + 2C{u_2}O + 2S{O_2} \uparrow $
So M is the mixture $C{u_2}O + C{u_2}S$
And then further Cuprous oxide and left behind Cuprous sulphide react together to form copper metal and sulphur dioxide gas.
$2C{u_2}O + C{u_2}S \to 6Cu + S{O_2} \uparrow $
As we can see, initially copper sulphide is reacted with air to form oxide and the remaining part of sulphide is reacted with this formed oxide to produce the metal further. This process is caked self reduction.
Therefore N is self reduction.
$2C{u_2}O + C{u_2}S\xrightarrow{{self\_reduction}}6Cu + S{O_2} \uparrow $
M is $C{u_2}O + C{u_2}S$ and N is self reduction.

Hence, the correct option is Option B.

Note:
Copper glance is cuprous sulphide not cupric sulphide. Copper exhibits variable valency. Cuprous ion is copper with +2 charge whereas cupric ion is copper with +3 charge. Be careful with this and always balance the reactions. In the self reduction process, no additional reducing agent is required to reduce the ore into the metal. Self reduction can be possible in only less electro-positive elements like Lead, Mercury, Copper etc.