Question

State Faraday's first law of electrolysis

Answer 1

Answer:

Faradays first electrolysis Law states that the quantity of reaction taking place in terms of mass of ions formed or discharged from an electrolyte is proportional to the amount of electric current passed. Since electric current (ampere) is the number of coulombs (Q) flowing in one second,

Mass of the ions formed or reacted (m) α electric current α Q ,

or m α Q, or m = ZQ ;

where, Z is a proportionality constant, called chemical equivalent of the element.

For a flow of, 1 Coulomb of charges for one second, m = Z.

The proportionality constant is equal to the mass of the substance involved in the reaction. Z is the electrochemical equivalent mass of one coulomb charge.

One coulomb of charge corresponds to a mass of one equivalent.

i) Electric current and Charge (Q)

Electric current is measured in ampere and it is the charges flowing per unit tome (seconds) = I = fracQt

Or Quantity of Charges flowing = Q = It = ampere seconds. m = ZIt

ii) Number of electrons – Charge Q of electrons – Faraday -Equivalent mass of substances

But the charges are associated with electrons. Every electron carries a charge of 1.6 × 10-19 coulombs.

Charges carried by one equivalent/ mole number of electrons(Q)= 6.02 × 1023 × 1.6 × 10-19 coulombs

= 96485 coulombs ≈ 96500C = 1 Faraday = 1F

One equivalent (or mole or Avogadro’s) of electrons α 96485 coulombs ≈ 96500C = 1 Faraday = 1F

iii) Mass of substance undergoing electrolysis

Faraday Law says, m = Z ×Q or m = Z I t.

When one coulomb corresponds to one electrochemical equivalent mass (Z) of the substance,

one equivalent(or mole) of electrons flowing per second, will correspond to 96485 Equivalents mass.

This, 96485 electrochemical equivalents = Z × 96485=Equivalent weight of substance in gram.

So, Electrochemical equivalent of a substance = Z = fracEquivalent,weight,of,substance,in,gram96485=fracE96485

Equivalent weight of a substance is, related to its molecular weight.

Equivalent mass of a substance = fracMolecular,eight,of,the,substanceValency,or,charge

For every, one mole of electrons or charges (1Faraday) or 96485ampere sec, passing through an

electrolyte, one equivalent mass of the electrolyte is reacted, discharged/deposited etc.

One Avogadro’s number of electrons = Charge of 1 Faraday = 96485coulombs = 96485ampere sec

= 1equivalent mass (reacted/deposited/neutralized)

Mass of the substance (gm) = Equivalent weight(gm) × fracCoulombs96485 = Equivalent weight(gm) × fracampere,sec96485

Or, m = fracEQ96485=fracEIt96485

Example:

For example, on passing electric current through a copper sulphate electrolyte solution, copper ions gets discharged and deposit on the anode.

Cu2+ + 2e– →Cu

Each copper ion needs two electrons for its reduction reaction to copper atom. More the electrons passing through the copper sulphate, solution more will be the copper ions being, deposited on the anode. Hence there is a direct relationship between the mass of material being, reduced and the numbers of electrons flowing into the electrolyte.

Here, one copper ion needs 2 electrons;so, One mole of copper ions needs 2 moles of electrons.

m = 2 × equivalent weight of copper

Explanation:

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