Faraday’s First Law of Electrolysis

Electroplating

The most important question regarding electroplating is the following: how is the amount of gold being deposited on the substrate (cathode) controlled?

The answer to this question lies in Faraday’s First Law of Electrolysis which states that ‘The mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electric charge at that electrode’

The electrochemical equivalent (Z), with S.I units kgC-1 or kgA-1s-1, is a constant for a particular substance, that tells us the mass of the substance deposited at an electrode when a certain amount of current is applied in a given period of time.

Mathematically:

(where: m = mass of material deposited; Q= Charge; I= Current; t= time; Z= electrochemical equivalent)

m ∞ Q
m ∞ I * t

m = Z * I * t

Z = m/ I * t

The electrochemical equivalent for Gold is 2.4496 gA-1hr-1, which means that if 1 Ampere of current is passed through the electrodes for 1 hour, 2.4496 grams of Gold will be deposited at the cathode. Using this, the current and time for electroplating can be fixed depending on the mass of gold that needs to be deposited.

The thickness of the gold layer deposited on the substrate can also be calculated using the density of gold:

(Let: Density = d; mass of gold deposited = m; volume of gold deposited = v; surface area of substrate = a; thickness of gold deposited = t)

d = m/ v

d= m/ a * t

t = m/ a * d

Using these principles, substances can be electroplated with a high degree of precision.

2 thoughts on “Faraday’s First Law of Electrolysis”

  1. Nicole's avatar

    This is very interesting – can you tell me what the typical thickness of electroplated objects are? How much gold do they actually put on the object?

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    1. divyanshupachisia's avatar

      Hey!
      The minimum thickness of gold for an object to be classified as a gold- electroplated object is as small as 7 millionths of an inch- if it is less than this it is considered a “gold wash”.
      The typical thickness of gold on an electroplated object is about 1 to 5 microns (10^(-6) meters).
      The amount of gold is therefore in minute quantities, which is probably due to the fact that gold is extremely expensive. As a result, the precision required is very high, making Faraday’s Law of Electrolysis extremely important!
      Thanks for the comment and hope that answered your question 🙂

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