A solution containing one mole per litre of each $Cu(NO_3)_2$, $AgNO_3,Hg_2(NO_3)_2$ and $Mg(NO_3)_2$ is being electrolysed by using inert electrodes. The values of standard electrode potentials in volts (reduction potential) are
$\hspace15mm Ag^+/ Ag =+0.80, Hg^{2+}_2/2Hg=+0.79 $
$\hspace15mm Cu^+/ Cu =+0.34, Mg^{2+}/Mg=-2.37 $
With increasing voltage, the sequence of deposition of metals or the cathode will be
- $Ag, Hg Cu, Mg$
- $Mg, Cu, Hg, Ag$
- $Ag, Hg, Cu$
- $Cu, Hg, Ag$
The Correct Option is C
Solution and Explanation
Therefore, in the present case, only Ag, Hg and Cu would be deposited on passing electricity through aqueous solution of these ions, Mg will not be deposited.
Also, higher the value of $E^\circ$, easier will be their reduction,therefore, the sequence in which ions will be deposited on increasing voltage across the electrodes is :
$\hspace35mm Ag, Hg, Cu$
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Concepts Used:
Electrochemical Cells
An electrochemical cell is a device that is used to create electrical energy through the chemical reactions which are involved in it. The electrical energy supplied to electrochemical cells is used to smooth the chemical reactions. In the electrochemical cell, the involved devices have the ability to convert the chemical energy to electrical energy or vice-versa.
Classification of Electrochemical Cell:
Cathode
- Denoted by a positive sign since electrons are consumed here
- A reduction reaction occurs in the cathode of an electrochemical cell
- Electrons move into the cathode
Anode
- Denoted by a negative sign since electrons are liberated here
- An oxidation reaction occurs here
- Electrons move out of the anode
Types of Electrochemical Cells:
Galvanic cells (also known as Voltaic cells)
- Chemical energy is transformed into electrical energy.
- The redox reactions are spontaneous in nature.
- The anode is negatively charged and the cathode is positively charged.
- The electrons originate from the species that undergo oxidation.
Electrolytic cells
- Electrical energy is transformed into chemical energy.
- The redox reactions are non-spontaneous.
- These cells are positively charged anode and negatively charged cathode.
- Electrons originate from an external source.