Question

Metals above hydrogen in the electrochemical series are active metals.

Answer 1

Answer:

y measuring the potentials of various electrodes versus stand­ard hydrogen electrode (SHE), a series of standard electrode potentials has been established.

When the electrodes (metals and non-metals) in contact with their ions are arranged on the basis of the values of their standard reduction potentials or standard oxidation potentials, the resulting series is called the electrochemical or electromotive or activity series of the elements.

By international convention, the standard potentials of electrodes are tabulated for reduction half reactions, indicating the tendencies of the electrodes to behave as cathodes towards SHE.

Electrodes with positive E° values for reduction half reactions do in fact act as cathodes versus SHE, while those with negative E° values of reduction half reactions behave instead as anodes versus SHE. The electrochemical series is shown in the follow­ing table.

Standard Aqueous Electrode 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

Explanation:

Answer 2

Explanation:

metals above hydrogen