What this calculator does
Electrolysis drives a non-spontaneous chemical reaction using an electric current, depositing or liberating an element at an electrode in proportion to the total electric charge passed. Michael Faraday's law of electrolysis quantifies exactly that relationship, connecting current, time, and the chemistry of the ion being reduced or oxidised to a mass of product.
The key link is the Faraday constant, the charge carried by one mole of electrons (96,485 coulombs per mole). Multiplying current by time gives total charge; dividing by the Faraday constant and the number of electrons each ion needs gives moles of product, and multiplying that by molar mass gives the mass deposited.
The formula
Multiply current by time (converted to seconds) to get total charge passed, in coulombs. Divide by the number of electrons transferred per ion and by the Faraday constant to get moles of product, then multiply by the molar mass of the substance to get the mass deposited.
| Term | Meaning |
|---|---|
| F (Faraday constant) | The charge carried by one mole of electrons, 96,485 coulombs per mole. |
| n | The number of electrons transferred per ion of the substance being deposited (2 for Cu²⁺ → Cu, 1 for Ag⁺ → Ag, and so on). |
| Q (charge) | Total electric charge passed through the cell: current × time, in coulombs. |
The inputs explained
| Field | What to enter |
|---|---|
| Current (A) | The constant current supplied to the electrolytic cell. |
| Time (min) | The duration the current was applied, entered in minutes. |
| Molar mass of substance (g/mol) | The molar mass of the element or compound being deposited or liberated. |
| Electrons transferred per ion (n) | The number of electrons needed to reduce or oxidise one ion of the substance, from its half-reaction. |
When to use it
Electroplating
Faraday's law predicts how much metal a given current and time will deposit onto a surface, which is the basis for controlling coating thickness in electroplating.
Industrial metal extraction
Processes such as aluminium smelting by electrolysis rely on this same relationship to relate power consumption to metal output at industrial scale.
Verifying a lab electrolysis result
Comparing a measured mass deposited against the mass predicted from current and time is a standard way to check the efficiency of an electrolysis setup, since real cells rarely achieve exactly 100% current efficiency.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How mass deposited changes with time
A constant 2 A current, run for a range of durations.
| Time | Mass deposited | Total charge passed |
|---|---|---|
| 10 min | 0.3952 g | 1,200 C |
| 20 min | 0.7904 g | 2,400 C |
| 30 min | 1.186 g | 3,600 C |
| 60 min | 2.371 g | 7,200 C |
| 90 min | 3.557 g | 10,800 C |
| 120 min | 4.742 g | 14,400 C |
How mass deposited changes with electrons transferred per ion
The same current and time, applied to ions needing different numbers of electrons.
| Electrons transferred (n) | Mass deposited | Moles deposited |
|---|---|---|
| 1 | 4.742 g | 0.074623 mol |
| 2 | 2.371 g | 0.0373115 mol |
| 3 | 1.581 g | 0.02487433 mol |
Questions
What is the Faraday constant and why is it fixed?
It is the total electric charge carried by one mole of electrons, 96,485 coulombs, a physical constant derived from the elementary charge and Avogadro's number. It does not vary by experiment, which is why it is built into the calculator rather than entered.
How do I know the value of n for a given ion?
It comes from the half-reaction for that ion: n is the number of electrons shown in the balanced half-equation, for example 2 for Cu²⁺ + 2e⁻ → Cu, or 1 for Ag⁺ + e⁻ → Ag.
Does this assume 100% current efficiency?
Yes. It calculates the theoretical maximum mass that the charge passed could deposit, assuming every electron goes toward the intended reaction. Real cells often have side reactions, so measured yields can be somewhat lower than this figure.
Can this be used for gas evolution instead of a solid deposit?
Yes, the same law applies to any electrode product, including gases such as hydrogen or oxygen liberated during electrolysis; the calculator gives moles and mass, and moles of gas can be converted to volume separately using the ideal gas law.
To convert the moles of gas this calculator predicts into a volume, see the molar mass of a gas calculator. For the electrochemical potential driving a cell rather than the mass it deposits, see the Nernst equation calculator.