Electrolysis

Electrolysis

Use the Electrolysis Calculator to find:

Quantity of a substance over a given period of time for a given electric current in amperes
Time measured in seconds or hours for a given quantity of substance for a given number of amperes
Current in amperes required to produce a given quantity of substance over a given period of time

Amps, Time, Coulombs, Faradays, and Moles of Electrons

Three equations relate these constants:

amperes x time = Coulombs
96,485 coulombs = 1 Faraday
1 Faraday = 1 mole of electrons

Calculating the Quantity of Substance Produced or Consumed

To determine the quantity of substance either produced or consumed during electrolysis given the time a known current flowed::

Write the balanced half-reactions involved.
Enter the number of amperes of current.
Enter the number seconds or hours of time that the substance will be produced/consumed at the electrode/anode.
The output of the Calculator is in grams of substance or the volume of gas produced.

Example: A 40.0 amp current flowed through molten iron(III) chloride for 10.0 hours (36,000 s). Determine the mass of iron and the volume of chlorine gas (measured at 25^oC and 1 atm) that is produced during this time.

Enter the part of the half-reaction equation that takes place at either the anode and at the cathode as shown. {Highlighted in RED}

anode (oxidation) 2 Cl^- Cl₂(g) + 2 e^-
OR
cathode (reduction) Fe³⁺ + 3 e^- Fe(s)

-->

Enter the current in Amperes, and the time in either seconds or hours.
Calculates the mass using molar mass of a substance or the volume of gas using the ideal gas law (PV = nRT) by selecting the option using the radio buttons.

Top

Calculating the Time Required

To determine the quantity of time required to produce a known quantity of a substance given the amount of current that flowed:

Enter the quantity of substance to be produced/consumed in moles.
Enter the balanced half-reaction involved.
Enter the number of Amperes available from the power source.

Example: How long must a 20.0 amp current flow through a solution of ZnSO₄ in order to produce 25.00 g of Zn metal.

Enter the desired mass of Zn to be produced and the molar mass of Zn.
Enter the half-reaction for the production of Zn at the cathode.
Zn²⁺(aq) + 2 e^- Zn(s)
Enter the current in amperes, then click on the Unknown button to find the length of time required to produce that quantity of a substance. The output Z= will be in seconds. Use the radio buttons to manipulate the output in the text box left blank for the calculation.

Top

Calculating the Current Required

To determine the amount of current necessary to produce a known quantity of substance in a given amount of time:

Find the quantity of substance produced/or consumed in moles.
Write the equation for the half-reaction taking place.
Calculate the number of moles of electrons required.
Convert the moles of electrons into coulombs of charge.
Calculate the current required.

Example: What current is required to produce 400.0 L of hydrogen gas, measured at STP, from the electrolysis of water in 1 hour (3600 s)?

Enter the desired volume of H₂. (Remember, at STP, 1 mole of any gas occupies 22.4 L.)
Write the equation for the half-reaction that takes place.
Hydrogen is produced during the reduction of water at the cathode. The equation for this half-reaction is:

4 e^- + 4 H₂O(l) 2 H₂(g) + 4 OH^-(aq)
Calculate the number of moles of electrons. According to the stoichiometry of the equation, 4 mole of e^- are required to produce 2 moles of hydrogen gas, or 2 moles of e^-'s for every one mole of hydrogen gas.
Enter the length of time desired in hours or seconds using the radio buttons. Then click on the Unknown button to calculate the current required.

Top