Faraday's Law of Electrolysis
Q = nFm/M relates charge passed to mass deposited. Faraday's laws provide quantitative electrodeposition—essential for electroplating, metal refining, and industrial electrolysis.
Why This Chemistry Calculation Matters
Why: Faraday's law enables precise electrodeposition control for plating, refining, and analytical chemistry. It links electrical charge to chemical amount.
How: m = (M×Q)/(n×F); Q = I×t. Solve for the unknown given mass, current, time, or charge.
- ●m = (M × I × t) / (n × F) — mass from current and time.
- ●One Faraday (96,485 C) deposits 1 mol of monovalent ions.
- ●Current efficiency < 100% in practice; use extended models for accuracy.
- ●Electroplating: control thickness via I, t, and electrode area.
Sample Examples
⚡ Copper Plating
Electroplating 5.0 g of copper at 2.5 A
🥈 Silver Refining
Producing 10.0 g of silver at 1.0 A for 2 hours
✈️ Aluminum Production
Hall-Héroult process: 1000 kg Al at 100 kA
🔩 Zinc Galvanizing
Galvanizing steel: 50 g Zn at 5.0 A
⚡ Charge from Mass
Calculate charge needed for 25 g of copper
🔋 Current from Charge
Find current for 1 Faraday of charge in 1 hour
🔧 Nickel Plating
Plating 15 g nickel at 3.0 A for 30 minutes
Calculate Electrolysis Parameters
Selected: Cu²⁺ (Copper(II)) | Charge: 2 | Molar Mass: 63.55 g/mol | Half-reaction: Cu²⁺ + 2e⁻ → Cu
⚠️For educational and informational purposes only. Verify with a qualified professional.
🔬 Chemistry Facts
Q = nFm/M — charge to mass for electrodeposition.
— IUPAC
F = 96,485 C/mol. Cu²⁺ (n=2): 2F per mol Cu.
— Electrochemistry
Hall-Héroult: Al³⁺ + 3e⁻ → Al. High energy process.
— Industry
Silver: 1F per mol; Zinc: 2F per mol.
— Faraday
What is Faraday's Law?
Faraday's Law of Electrolysis, discovered by Michael Faraday in the 1830s, describes the quantitative relationship between electricity and chemical change during electrolysis. It states that the amount of substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed through the electrolyte.
⚡ The Two Laws
First Law
The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity (charge) passed through the electrolyte.
Second Law
When the same quantity of electricity passes through different electrolytes, the masses of substances deposited are proportional to their equivalent weights.
How Faraday's Law Works
Electrolysis involves passing an electric current through an electrolyte, causing chemical reactions at the electrodes. The amount of substance produced depends on the charge passed, which equals current multiplied by time.
🔬 The Electrolysis Process
Electric Current Applied
Direct current flows through the electrolyte, creating a potential difference between electrodes.
Ion Migration
Cations move toward the cathode (negative electrode), anions toward the anode (positive electrode).
Electrode Reactions
At the cathode: reduction (gain of electrons). At the anode: oxidation (loss of electrons).
Mass Deposition
Metal ions are reduced to solid metal, depositing on the cathode surface.
When to Use Faraday's Law
Faraday's Law calculations are essential in numerous industrial and laboratory applications involving electrolysis processes.
Electroplating
Calculate coating thickness, deposition time, and current requirements for plating metals like copper, nickel, chromium, and gold onto surfaces.
- Copper plating
- Chrome plating
- Nickel plating
- Gold electroplating
Metal Refining
Determine production rates and energy requirements for electrorefining processes that purify metals like copper, silver, and lead.
- Copper electrorefining
- Silver refining
- Lead purification
- Zinc electrowinning
Battery Production
Calculate electrode material requirements and charging/discharging characteristics for battery manufacturing.
- Lead-acid batteries
- Nickel-cadmium cells
- Lithium-ion electrodes
- Battery capacity
Aluminum Production
Calculate production rates for the Hall-Héroult process, which produces millions of tons of aluminum annually using electrolysis.
- Hall-Héroult process
- Energy consumption
- Production optimization
- Cost analysis
Analytical Chemistry
Determine metal concentrations using coulometric titrations and electrogravimetric analysis techniques.
- Coulometric analysis
- Electrogravimetry
- Metal ion determination
- Quality control
Corrosion Protection
Calculate zinc coating thickness for galvanizing steel to prevent rust and extend material lifespan.
- Hot-dip galvanizing
- Electrogalvanizing
- Coating thickness
- Protection duration
Faraday's Law Formulas
Main Formula
Where: m = mass (g), M = molar mass (g/mol), I = current (A), t = time (s), n = number of electrons, F = Faraday's constant (96485 C/mol)
Charge Calculation
Q = n × F × (moles of substance)
Charge in Coulombs (C) or Faradays (F), where 1 F = 96485 C
Moles of Electrons
The number of moles of electrons transferred equals the charge divided by Faraday's constant
Current Efficiency
Actual mass = Theoretical mass × (Efficiency / 100)
Accounts for side reactions and losses in real electrolysis processes
Rearranged Formulas
Common Ions and Their Properties
| Ion | Name | Charge (n) | Molar Mass (g/mol) | Half-Reaction | Applications |
|---|---|---|---|---|---|
| Cu²⁺ | Copper(II) | 2 | 63.55 | Cu²⁺ + 2e⁻ → Cu | Copper plating |
| Ag⁺ | Silver | 1 | 107.87 | Ag⁺ + e⁻ → Ag | Silver refining |
| Zn²⁺ | Zinc | 2 | 65.38 | Zn²⁺ + 2e⁻ → Zn | Galvanizing |
| Al³⁺ | Aluminum | 3 | 26.98 | Al³⁺ + 3e⁻ → Al | Aluminum production |
| Na⁺ | Sodium | 1 | 22.99 | Na⁺ + e⁻ → Na | Sodium production |
| Fe²⁺ | Iron(II) | 2 | 55.84 | Fe²⁺ + 2e⁻ → Fe | Steel production |
| Ni²⁺ | Nickel | 2 | 58.69 | Ni²⁺ + 2e⁻ → Ni | Nickel plating |
| Cr³⁺ | Chromium(III) | 3 | 52.00 | Cr³⁺ + 3e⁻ → Cr | Chrome plating |