Question

The metal extracted by leaching with a cyanide is:
A.\[Al\]
B.$Na$
C.$Ag$
D.$Cu$

Answer 1

Hint: Try to remember the extraction process of each metal given in the options. Extraction of metal by leaching with cyanide is specific for some limited metals. Try to recollect those metals and then filter the options.

Complete step by step answer:
Here we are discussing leaching of metals with cyanide. First let us see what basically is leaching.
Leaching is the process of removal of inorganic or organic impurities from solid phase into a water phase, by processes such as desorption, complexation and mineral dissolution. We can see examples of leaching everywhere. Like water leaches everything that comes in contact with it from the surface of the matter.
The metals we have here are aluminium \[(Al)\] , sodium $(Na)$ , silver $(Ag)$ and copper $(Cu)$ . From the theory of metallurgy we know that extraction of precious metals like silver and gold is done by cyanide process.
In the cyanide process, the ores of gold or silver are dissolved in a dilute solution of sodium cyanide. First, the ore is contacted with cyanide solution. Then solids are separated from the clear solution. Last the metal is recovered from the solution by precipitating with zinc dust.
Now we will look at the process through the reactions involved in the process.
At Cathode:
Reduction of gold or silver happens at cathode
${[Ag{(CN)_2}]^ - } + {e^ - } \to Ag + 2C{N^ - }$
Silver is reduced by gaining electrons or we can say by decrease in its oxidation number.
At Anode:
Oxidation of zinc happens at anode
$Zn + 2O{H^ - } \to Zn{(OH)_2} + 2{e^ - }$
Zinc is oxidised by losing electrons or we can say by increase in its oxidation number.
Last the residue cyanide needs to be removed in some way.
$Zn{(OH)_2} + 4C{N^ - } \to Zn{(CN)_4}^{2 - } + 2O{H^ - }$
Hence through our understanding of the process we can say silver is extracted via leaching with cyanide.
Hence option C is the correct answer.

Note:
Having the knowledge of extraction of each significant matter is important in metallurgy. Though explaining extraction via reactions is recommended , remember to balance the reactions.