Question

In industry, copper metal is purified by electrolysis. Which changes occur to the masses of the electrodes and to the color of the electrolyte during this process?
A. Mass of anode-decrease, mass of cathode-increase, color of electrolyte-little or no change occurs
B. Mass of anode-decrease, mass of cathode-increase, color of electrolyte-pale blue to blue
C. Mass of anode-increase, mass of cathode-decrease, color of electrolyte-little or no change occurs
D. Mass of anode-increase, mass of cathode-decrease, color of electrolyte-blue to pale blue

Answer 1

Hint: In purification of copper metal, the copper gets deposited on the negative electrode and on the positive electrode the copper gets dissolved in the solution which results in change in masses of electrodes whereas the electrolyte remains the same with no or minute change.

Complete step by step answer:
Electrolysis decomposes the ionic substances when an electric current is passed through them. It helps in the extraction of metals or even in purification of metals too.
Purification of copper is also done through electrolysis. Now, what happens?
The two electrodes i.e. anode (positive electrode) and cathode (negative electrode) are taken. The anode is made from impure copper and the cathode is made from pure copper. And one important thing, the solution containing copper compounds is chosen as an electrolyte for the whole process for ex. Copper sulphate, ${\text{CuS}}{{\text{O}}_{\text{4}}}$. During electrolysis, the anode loses some of its mass as copper from anode is dissolved in the electrolyte solution and cathode gains some mass as copper gets deposited on it.
Reactions occurring at anode:
${\text{Cu}} \to {\text{C}}{{\text{u}}^{{\text{2 + }}}}{\text{ + 2}}{{\text{e}}^{\text{ - }}}$(oxidation occurs)
Reactions occurring at cathode:
${\text{C}}{{\text{u}}^{{\text{2 + }}}}{\text{ + 2}}{{\text{e}}^{\text{ - }}} \to {\text{Cu}}$ (reduction occurs)
Basically, the ${\text{C}}{{\text{u}}^{{\text{2 + }}}}$ ions that are lost from anode are gained by cathode respectively and we get the pure copper at the cathode. That’s how the whole purification process takes place in itself.
So, option A is correct that says the mass of anode decreases and the mass of cathode increases provided with little or no changes in the electrolyte.

Note:
Always the anode is made from impure metal and the cathode is made from pure metal. Keep this thing in mind while dealing with the purification process involving electrolysis. The movement of electrons will always be from anode to cathode.