• Created by: Saarah17
  • Created on: 24-10-22 21:18

What is electrolysis?

{oxidation -> electrons are lost and on the right-hand side of the arrow
reduction -> electrons are gained and on the left-hand side of the arrow}

—> the decomposition of a compound using electricity.

—> ionic substance decompose by an electrical charge being passed through them during electrolysis.

—> ions MUST be free to move, compounds are either molten or in solution.

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—> anode : positive electrode (attracts anions)

—> cathode : negative electrode (attracts cations)

—> the only ions present are sodium and chloride ions so only sodium and chlorine is produced.

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In solution - dissolved in water

—> H+ and OH- ions are also present

—> chlorine is still produced on the anode end

—> hydrogen is produced on the cathode end rather than sodium

—> only one type of ion can be discharged (released as a molecule/atom) at each electrode

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What happens in solution?

—> the position of the ion in the electrochemical series affects its ease of discharge at an electrode

—> when metals react or is placed in water, they lose electrons and become cations

—> this attracts the negative electrons back to the metal - equilibrium

—> Cu is less reactive than Mg so it is less likely to become oxidised (POE moves right)

Mg2+ + 2e- -> Mg

Cu2+ (aq) + 2e- -><- Cu (s)

E° = +0.34 V

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How to decide which ions discharge at each electro

—> a potential difference exists between the metal and the solution it is around

—> standard electrode potentials are a measure of the potential difference that can exist between metals and their solutions

—> the more negative the value, the more likely it oxidises - loses electrons, become a positive ion

—> the less negative the value, the less likely it oxidises - gains electrons, become a negative ion

—> the more positive cation, is more likely to get discharged at the cathode

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Back to sodium chloride solution

—> sodium has a SEP of -2.71 // hydrogen has a SEP of 0

—> hydrogen has a more positive SEP value therefore it it more likely to get discharged at the cathode

{SEP : standard electrode potential}

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Effects of concentration on the ion discharged

—> higher the concentration of the ion, the more likely it is to be discharged - no matter what the SEP is

—> E.g. If the lead sodium chloride solution used was of a higher concentration, lead would be discharged rather than hydrogen

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