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Solution


Q.

Given below are two statements:  

1 M aqueous solution of each of Cu(NO3)2, AgNO3, Hg2(NO3)2, Mg(NO3)2 are electrolysed using inert electrodes.  

Given:  
EAg+/Ag⊖=0.80 V,  EHg22+/Hg⊖=0.79 V

ECu2+/Cu⊖=0.24 V,  EMg2+/Mg⊖=-2.37 V

Statement (I): With increasing voltage, the sequence of deposition of metals on the cathode will be Ag, Hg and Cu.  

Statement (II): Magnesium will not be deposited at cathode; instead oxygen gas will be evolved at the cathode.  

In the light of the above statement, choose the most appropriate answer from the options given below:          [2025]
1 Both statement I and statement II are incorrect.   
2 Statement I is correct but statement II is incorrect.    
3 Both statement I and statement II are correct.  
4 Statement I is incorrect but statement II is correct.  

Ans.

(2)

Statement I: Elements with more reduction potential are preferably reduced at cathode. So order of reduction at cathode is: Ag(EAg+/Ag∘=0.80 V)>Hg(EHg22+/Hg∘=0.79 V)>Cu(ECu2+/Cu∘=0.34 V)

Statement II: At cathode reduction occurs, not oxidation. So by reduction of water at cathode, hydrogen gas is evolved (EH2O/H2∘=-0.83 V); in preference to reduction of Mg (EMg2+/Mg∘=-2.37 V).