Electrolysis
Introduced| English | Meaning |
|---|---|
| electrolysis/ɪlekˈtrɒləsɪs/ | The decomposition of an electrolyte by an electric current passing through its molten form or a solution. |
| electrolyte/ɪˈlektrəlaɪt/ | A substance that conducts electricity when molten or dissolved because it contains mobile ions. |
| electrode/ɪˈlektrəʊd/ | A conductor through which charge enters or leaves an electrochemical system. |
| cathode/ˈkæθəʊd/ | An electrode at which reduction occurs. |
| anode/ˈænəʊd/ | An electrode at which oxidation occurs. |
| Faraday constant/ˈfærədeɪ ˈkɒnstənt/ | The charge on one mole of electrons: F ≈ 96,500 C mol^-1. |
Splitting with electricity
- Electrolysis 电解 uses electricity to break down a molten or aqueous electrolyte 电解质.
- A half-reaction happens at each electrode 电极.
- You can predict the products and calculate amounts.
During electrolysis, positive ions move to the negative electrode, the ______.
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Reduction occurs at the cathode.
The two electrodes
- at the cathode 阴极 (negative): positive ions gain electrons (reduction).
- at the anode 阳极 (positive): negative ions lose electrons (oxidation).
A simple cell with a salt bridge and voltmeter
Inside the electrolysis cell
Step through it: free ions in the electrolyte migrate to the oppositely-charged electrode, then are discharged — cations gain electrons at the cathode (reduction), anions lose them at the anode (oxidation).
At the cathode (negative electrode) in electrolysis:
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Positive ions are attracted to the cathode and gain electrons (reduction); the anode does oxidation.
Match each electrolysis fact.
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Each item links the term to its correct meaning.
Predicting the products
- a molten electrolyte → metal at the cathode, non-metal at the anode.
- an aqueous one also has water: a reactive metal gives hydrogen instead at the cathode; the anode usually gives oxygen, but a concentrated halide gives the halogen.
A Hofmann voltameter for the electrolysis of water: a power supply drives current through two electrodes, and the gases made at each one collect in the side tubes
Electrolysing an aqueous solution of a reactive metal salt gives, at the cathode:
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For a reactive metal, water is reduced to hydrogen at the cathode instead of the metal.
Calculations
- the Faraday constant 法拉第常量 $F = Le$ (charge on one mole of electrons). Charge passed $Q = It$.
- moles of electrons $= Q / F$.
- use the half-equation to find moles of product.
- find the mass ($\times M_r$) or gas volume.
A molten electrolyte gives the metal and non-metal; aqueous also has water
Faraday's first law
m = k·Q
Mass deposited is proportional to the charge passed (Faraday's law).
The charge passed during electrolysis is given by:
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Q = It; then moles of electrons = Q/F, and the half-equation gives the moles of product.
The Faraday constant F is:
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F = L × e, the charge carried by one mole of electrons.
You've got it
- cathode (−): reduction (gain electrons); anode (+): oxidation (lose electrons)
- molten → metal + non-metal; aqueous → hydrogen for reactive metals, halogen from concentrated halides
- $Q = It$; moles of electrons $= Q/F$ ($F = Le$); then use the half-equation for the product