Electrolysis of Molten Ionic Compounds Using Inert Electrodes

• E.g. for molten sodium chloride

1. Why must electrolyte be heated strongly throughout process of electrolysis

• Only when electrolyte → is molten/aqueous solution → can ions move freely throughout substance and migrate to oppositely charged electrodes and electrolysis can take place
• Sodium chloride → ionic compound → has high melting point. At r.t.p → sodium chloride is in solid state. Thus → large amount of heat has to be provided → to overcome strong electrostatic forces of attraction → which hold the sodium and chloride ions → in fixed positions → in the giant ionic lattice structure to melt this substance. Properties of Ionic Compounds
• Only when substance has melted → it must be heated continuously → to ensure → that temperature remains above → melting point → for electrolysis to take place continuously
• If heating stops → temperature of sodium chloride → will eventually decrease → until sodium chloride solidifies → and electrolysis will no longer take place → ions can no longer move freely and be attracted to oppositely charged electrodes.

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2. Which ion will migrate to positive electrode?

• Chloride ion (opp. charges attract, thus positive electrode → which is anode → attract negative ions which are anions)

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3. Describe what Happened to ions at positive electrode

• chloride ions → are discharged → as they undergo oxidation → by losing electrons → to form $C{l}_2$ (or chlorine molecules)

Note

Term ‘discharged’ means undergo reaction → resulting in charge being removed.

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4. equation for reaction which takes place at positive electrode. include state symbols

• $2C{l}^{-}(l)\to C{l}_2(g)+2e^{-}$

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5. describe what was observed at the positive electrode during electrolysis

• pale yellow-green gas → evolved → around anode during electrolysis (chlorine, found in Group Properties - Group 17 Elements (Halogens))

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6. which ion will migrate to negative electrode

• Sodium Ion, $N{a}^{+}$

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7. Describe what happened to the ions at the negative electrode

• $N{a}^{+}$ will gain electron, and undergo reduction to form sodium.

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8. write an equation for the reaction which takes place at the negative electrode. include state symbols

• $N{a}^{+}(l)+e^{-}->Na(l)$

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9. describe what was observed at negative electrode during electrolysis

• tiny globules of molten sodium float to surface of molten sodium chloride (1)
• sodium burns in air with flashes of yellow light (1) (no need to identify as sodium, for colour → Group Properties - Group 1 Elements (Alkali Metals))

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10. write overall equation for electrolysis of molten sodium chloride. include state symbols

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