Question

Identify the substance underlines in each of the following cases –
The electrolyte used for electroplating an article with silver.

Answer 1

Hint: A complex salt which when dissolved in water forms an aqueous solution giving $A{g^ + }$ ions such that the migration of these ions is slow to ensure smooth deposition. With Silver Nitrate as electrolyte the deposition is not smooth though. So we look for some other possible electrolyte.

Complete step-by-step answer:
Electroplating can be defined as the electrolytic process of decomposition of a superior/dominating metal on the surface of a base/inferior metal that can also be an article. The process of electroplating forms a very thin coating of silver and other expensive superior metals on the surfaces of cheaper metals in order to give them the appearance and the chemical resistance of the costlier and superior metals.

In the process of electroplating with silver, the object to be plated (any article made of relatively cheaper material) is formed as the cathode of an electrolytic cell.
The anode is a bar of silver metal that is the superior metal, and the electrolyte (the liquid in between the electrodes) that is generally used is a solution of sodium argentocyanide, $Na\left[ {Ag{{\left( {CN} \right)}^{_{_{_{_{_{_{_{_2}}}}}}}}}} \right]$ , in water.

The reaction that takes place at cathode is –
$A{g^ + } + {e^ - } \to Ag$
The reaction that takes place at anode is –
$Ag \to A{g^ + } + {e^ - }$

Therefore an aqueous solution of sodium argentocyanide is the electrolyte that is used for the electrolysis of silver as the migration of Ag+ ions is slow in this solution as compared to $AgNO_3$ ​which helps to attain an even deposition of silver metal.

Note – Sodium Argentocyanide is a complex salt and it is preferred to silver nitrate as an electrolyte because deposition of silver on the cathode is not uniform as it is considerably a strong electrolyte. The condition that ensures that deposition is smooth in case of electroplating using sodium argentocyanide as electrolyte is that a small current should be passed for a longer period of time.