Chemistry - Electrolysis

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13 Terms

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Why do covalent compounds not conduct electricity?

There are no freely moving charged particles

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When do ionic compounds conduct electricity?

When molten or in an aqueous solution

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Why do ionic compounds only conduct electricity when molten or in an aqueous solution?

The ionic bonds are broken, allowing ions to move freely.

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Anion

Negatively charged ion

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Cation

Positively charged ion

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Electrolysis

  • Binary ionic compound are compounds consisting of just two elements joined together by ionic bonding

    • E.g. lead(II) bromide

  • These compounds undergo electrolysis and always produce their corresponding element

  • The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode

  • Therefore the cathode product will always be the metal and the product formed at the anode will always be the non-metal

<ul><li><p>Binary ionic compound are compounds consisting of just two elements joined together by ionic bonding</p><ul><li><p>E.g. lead(II) bromide</p></li></ul></li><li><p>These compounds undergo electrolysis and always produce their corresponding element</p></li><li><p>The<strong>&nbsp;positive</strong>&nbsp;ion will migrate towards the&nbsp;<strong>cathode</strong>&nbsp;and the&nbsp;<strong>negative</strong>&nbsp;ion will migrate towards the&nbsp;<strong>anode</strong></p></li><li><p>Therefore the&nbsp;<strong>cathode</strong>&nbsp;product will always be the metal and the product formed at the&nbsp;<strong>anode</strong>&nbsp;will always be the<strong> non-metal</strong></p></li></ul><p></p>
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Electrolysis Method

  1. Add lead(II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge

  2. Add two graphite rods as the electrodes and connect this to a power pack or battery

  3. Turn on the power pack or battery and allow electrolysis to take place

<ol><li><p>Add lead(II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge</p></li><li><p>Add two graphite rods as the electrodes and connect this to a power pack or battery</p></li><li><p>Turn on the power pack or battery and allow electrolysis to take place</p></li></ol><p></p>
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What happens at the anode?

  • Negative bromide ions move to the positive electrode (anode)

  • At the anode, they lose two electrons to form bromine molecules

  • There is bubbling at the anode as brown bromine gas is given off

  • The negatively charged ions lose electrons and are thus oxidised

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What happens at the cathode?

  • Positive lead ions move to the negative electrode (cathode)

  • At the cathode they gain electrons to form grey lead metal 

  • The lead deposits on the bottom of the electrode

  • The positively charged ions gain electrons and are thus reduced

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Oxidation (electrons)

When a substance loses electrons (OILRIG)

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Reduction (electrons)

When a substance gains electrons (OILRIG)

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In the electrolysis of molten lead(II) bromide the half equation at the negative electrode (cathode) is:

Pb2+ + 2e– ⟶ Pb         Reduction

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At the positive electrode (anode) bromine gas is produced by the discharge of bromide ions:

2Br– – 2e– ⟶ Br2          Oxidation

OR

2Br– ⟶ Br2  + 2e–