(b) State and explain Faraday's law of electrolysis. [3+1] Calculate the mass of silver separated on passage of 96.5 amp. of current for 30 minutes
Answers
Explanation:
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)∝ electric current α Q, or
m ∝ Q or
m = ZQ
Where, Z is a proportionality constant, called the 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 time (seconds).
I =
Q
t
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 ∝ 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 =
E
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Equivalent weight of a substance is, related to its molecular weight.
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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) ×
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