Chapter 19.8, Problem 2PE

Interpretation Introduction

Interpretation:

The current (in amperes) is passed that through an electrolytic cell containing molten ${\text{MgCl}}_2$ has to be calculated.

Concept introduction:

Standard reduction potential: The voltage associated with a reduction reaction at an electrode when all solutes are 1M and all gases are at 1 atm. The hydrogen electrode is called the standard hydrogen electrode (SHE).

Standard emf: E^o_cell is composed of a contribution from the anode and a contribution from the cathode is given by,

$E_{cell}^o=E_{cathode}^o-E_{anode}^o$

Where both $E_{cathode}^o$ and $E_{anode}^o$ are the standard reduction potentials of the electrodes.

Electrolysis: The process in which electrical energy is used to cause a non-spontaneous chemical reaction to occur. An electrolytic cell is an apparatus for carrying out electrolysis.

In a spontaneous reaction standard emf of a reaction is positive; if the value if negative then it is non-spontaneous and external energy (electrical energy) is applied to carry out that reaction.

During electrolysis, cations are reduced at cathode and anions are oxidized at anode. And in aqueous solutions water itself may be oxidized and/or reduced depends on the nature of other species involved/ present.

Quantitative aspects of Electrolysis:

The mass of product formed (or reactant consumed) at an electrode is proportional to both the amount of electricity transferred at the electrode and the molar mass of the substance.

The mass of product is calculated as follows,

• Convert Current into coulomb using $\left(\text{Current}\right)\times \left(time\right)\text{=}\text{no}\text{.of}\text{Coulomb}$
• Convert number of Coulombs into mole of electrons using $\text{mole}\text{of}{\text{e}}^{\text{-}}\text{=}\frac{\text{no}\text{.of}\text{Coulomb}}{\text{Faraday}\text{constant}}$