Q1(e). Electrochemical series and its significance

Answer in brief

The electrochemical series is the list of redox couples in the order of their standard reduction potentials E°; it ranks oxidising and reducing agents and shows which way a redox reaction will go.

Key points

• E° of a couple is the e.m.f. of a cell with that electrode on the right and the standard hydrogen electrode on the left, all species at unit activity.
• A high E° marks a strong oxidising agent (F₂, +2.87 V); a low E° a strong reducing agent (Li, −3.05 V).
• A metal displaces from solution the ions of any metal of higher E°; metals with negative E° liberate H₂ from dilute acids.
• E°cell = E°(cathode) − E°(anode); ΔG° = −nFE°cell, so the reaction is spontaneous when E°cell > 0 (Daniell cell 1.10 V).
• It predicts the order of discharge in electrolysis, sacrificial protection of iron by zinc and the disproportionation of Cu⁺.