Electrolysis

Defining Electrolysis
How Electrolysis works
Types of Electrolytes
Observations and half equations
Apparatus used to electrolyse dilute sulphuric acid
Apparatus used to electrolyse a molten electrolyte
Apparatus used to electrolyse a solution
Extraction of Aluminium
Refining of Copper
The economics of electrolysis
Typical Questions

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  • Created by: Rachael
  • Created on: 08-05-12 09:36

Defining Electrolysis

Two graphite rods, placed in a liquid and connected externally to a power supply can be used to test if a liquid conducts electricity. If a liquid conducts electricity and is decomposed by it, electrolysis is taking place.

"Electrolysis is the decomposition of a liquid electrolyte using a direct current of electricity."

The electrolyte is the liquid or solution which conducts electricity and is decomposed by it. The graphite rods are called electrodes. Graphite is used because it conducts electricity and is unreactive. More inert (unreactive) materials such as titanium or platinum are sometimes used

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How electrolysis works

All electrolytes conduct electricity as they have free ions that can move and carry charge.

When these positive and negative electrons are free to move, the positive ions (cations) move to the negative electrode (cathode) and the negative ions (anions) move to the positive electrode (anode).

The positive cations at the negative electrode gain electrons to become atoms (which may combine to form diatomic molecules in the case of H2)

The negative anions at the positive electrode lose electrons to become atoms (which may combine to form diatomic molecules for all other diatomics).

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Types of electrolysis

Molten Ionic Compounds

  • Lithium chloride (LiCl)
  • Lead bromide (PbBr2)

Aqueous Ionic Compounds

  • Copper (II) sulphate (CuSO4)
  • Sodium chloride (NaCl)

Acids

  • Dilute sulphuric acid (H2SO4)
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Observations and half equations

Molt Lithium Chloride, Molten Lead Bromide & Aqueou Sodium Chloride

Molten LiCl
Anode: Yellow-green pungent gas evolved
             2Cl(-) = Cl2 + 2e
Cathode: Silvery-grey liquid formed
               Li(+) + e(-) = Li

Molten PbBr2
Anode: Red-brown pungent gas evolved
           2Br(-) = Br2 + 2e(-)
Cathode: Silvery-grey liquid formed which sinks to bottom
              Pb(2+) + 2e(-) = Pb

Aqueous NaCl
Anode: Yellow-green pungent gas evolved

Cathode: Colourless, odourless gas evolved
                2H(+) + 2e(-) = H2


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Comments

Layal Christina Ferzoli

i found some of these cards very helpfull coz i found electrolysis really hard to understand. Thank you :) x

Nathan Birtwell

I have learnt more here than what my useless teacher has taught me in a year!!! :L Good notes and easy to understand!! :D

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