Intermediate Topic 570 of 1102 Acids, Bases & Electrochemistry
Faraday's First Law
Mass deposited during electrolysis is proportional to the charge passed.
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In-depth explanation of Faraday's First Law
Faraday's first law states that the mass of substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electric charge passed through the cell. It can be written m = (Q/F)(M/n) = (I t M)/(n F), where Q is the charge, I the current, t the time, M the molar mass and n the number of electrons per ion. The law reflects the fact that each electron transferred produces a fixed amount of product. It is used to calculate plating thickness, the time needed for a given deposit and the efficiency of an electrolysis.
Going deeper: Faraday's First Law
Key ideas: Mass deposited is proportional to charge passed: m = (M x I x t)/(n x F). Example: 2.0 A for 30 min gives 3600 C, which is 0.0373 mol e-, so 1.18 g of Cu (n = 2, M = 63.5). Equivalent mass = M/n, and m = Z Q with Z = M/(nF) the electrochemical equivalent.
Common mistakes and connections: Common errors: using minutes instead of seconds, wrong n, and assuming 100 percent current efficiency when side reactions occur. Divide by efficiency if given. A constant-current source is needed for Q = I t; if current varies, integrate. Links to quantitative electroplating and electrorefining.
Visualization of Faraday's First Law
Faraday first law: mass deposited grows in direct proportion to charge passed, so 2.0 A for 30 minutes plates about 1.19 g of copper. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Passing 2.0 A for 30 minutes through a copper(II) solution deposits about 1.19 g of copper.
Frequently asked questions about Faraday's First Law
What is Faraday's First Law?
Mass deposited during electrolysis is proportional to the charge passed.
Is Faraday's First Law a beginner, intermediate or advanced topic?
Faraday's First Law is a intermediate topic in Acids, Bases & Electrochemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Faraday's First Law?
Study these earlier topics in Acids, Bases & Electrochemistry first: Cell Potential and Equilibrium, Concentration Cells, Faraday's Constant.
What comes after Faraday's First Law?
The next topics in Acids, Bases & Electrochemistry are Faraday's Second Law and Electrolysis of Molten Salts.
Can I practise Faraday's First Law with quizzes?
Yes. The interactive lesson includes a self-check question on Faraday's First Law, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Where Faraday's First Law fits in Acids, Bases & Electrochemistry
Faraday's First Law is topic 60 of 105 in Acids, Bases & Electrochemistry.