PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 354

Example

During electrolytic refining of copper, raw copper forms the anode and an aqueous solution of

copper sulfate forms the electrolyte. Copper dissolution occurs at the anode

Cu = Cu2++ 2 e−.

while electrolytically pure copper is discharged at the cathode. The anode is the active electrode

and the cathode is the inert electrode in this case.

11.2.2 Faraday’s law

Faraday’s law relates the electric chargeQ, which passes through a system during electrolysis,
with the amount of substance of the ionnidischarged at the electrode

ni=

Q

ziF

, (11.6)

whereziis the ion charge.F is theFaraday constantwhich is, but for the sign, equal to the
charge of 1 mole of electrons

F=NA|e−|= 96485.3 C mol−^1. (11.7)

Given that the charge is the product of the electric currentIand the time of electrolysisτ,

Q=I τ ,

mi=

MiI τ

ziF

, (11.8)

whereMiis the molecular mass of the ion.

Note: If a charge of 1F passes through a system, then 1 mole of univalent anions (or

1/2 mole of bivalent anions, etc.) reacts at the anode, and at the same time 1 mole of

univalent cations (or 1/2 mole of bivalent cations, etc.) reacts at the cathode.