Question

which of the following will form the cathode with respect to iron anode in an electrolytic cell:

a)Mg

b)Al

c)Cu

d)Zn

[Doubt: pls explain Concept and reason for answer]

Answer 1

Cu


Because all other are above Fe in elecrochemica series



​​​​​​​The electrochemical series is a list of metals and other substances arranged in rank order of how easily their atoms may lose electrons. ... The electrode potentials are arranged in the substances ability to donate its electrons; that is, how easily They are oxidised

ectrode Potentials at 25°C 'The Electrochemical Series'

Element	Electrode Reaction (Reduction)	Standard Electrode Reduction potential Eo, volt
Li	Li+ + e- → Li	-3.05
K	K+ + e- → K	-2.925
Ca	Ca2+ + 2e- → Ca	-2.87
Na	Na+ + e- → Na	-2.714
Mg	Mg2+ + 2e- → Mg	-2.37
Al	Al3+ + 3e- → Al	-1.66
Zn	Zn2+ + 2e- → Zn	-0.7628
Cr	Cr3+ + 3e- → Cr	-0.74
Fe	Fe2+ + 2e- → Fe	-0.44
Cd	Cd2+ + 2e- → Cd	-0.403
Ni	Ni2+ + 2e- → Ni	-0.25
Sn	Sn2+ + 2e- → Sn	-0.14
H2	2H+ + 2e- → H2	0.00
Cu	Cu2+ + 2e- → Cu	+0.337
I2	I2 + 2e- → 2I-	+0.535
Ag	Ag+ + e- → Ag	+0.799
Hg	Hg2+ + 2e- → Hg	+0.885
Br2	Br2 + 2e- → 2Br-	+1.08
Cl2	Cl2 + 2e- → 2Cl-	+1.36
Au	Au3+ + 3e- → Au	+1.50
F2	F2 + 2e- → 2F-	+2.87

The negative sign of standard reduction potential indicates that an electrode when joined with SHE acts as anode and oxidation occurs on this electrode.

For example, standard reduction potential of zinc is -0.76 volt.

When zinc electrode is joined with SHE, it acts as anode (-ve electrode) i.e., oxidation occurs on this electrode. Similarly, the +ve sign of standard reduction potential indicates that the electrode when joined with SHE acts as cathode and reduction occurs on this electrode.

Characteristics of Electrochemical Series

• The substances which are stronger reducing agents than hydrogen are placed above hydrogen in the series and have negative values of standard reduction potentials.

• All those substances which have positive values of reduction potentials and placed below hydrogen in the series are weaker reducing agents than hydrogen.

• The substances which are stronger oxidising agents than H+ion are placed below hydrogen in the series.

• The metals on the top (having high negative values of standard reduction potentials) have the tendency to lose electrons readily. These are active metals.

• The activity of metals decreases from top to bottom.

• The non-metals on the bottom (having high positive values of standard reduction potentials)

• have the tendency to accept electrons readily. These are active non-metals.

• The activity of non-metals increases from top to bottom.