FLOWING MERCURY CELL

KEYS

1 2

Cell: flowing mercury cell, membrane cell

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0

Whole cell

P

Power on / off

X

Remove the membrane (membrane cell)

Space

Pause

S

Speed 1× / ½× / ¼×

R

Restart with fresh brine

M

Graph on / off

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MODEL

• Schematic model: each particle stands for a very large number of particles. Water molecules are only drawn where they react.
• Stage 1 switches the power off; stages 2–4 switch it on.
• Anode: 2Cl⁻(aq) → Cl₂(g) + 2e⁻. Each Cl⁻ gives up an electron (it travels up the anode) and two Cl atoms join to form Cl₂.
• Mercury cell: Na⁺(aq) + e⁻ → Na(s), Na(s) + Hg(l) → Na/Hg(l); decomposer: 2Na/Hg(l) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + 2Hg(l). The mercury is pumped back.
• Membrane cell cathode: 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq). The membrane lets Na⁺ through but not Cl⁻ or OH⁻.
• Remove membrane: Cl₂ reacts with OH⁻: Cl₂(g) + 2OH⁻(aq) → Cl⁻(aq) + OCl⁻(aq) + H₂O(l), so the NaOH(aq) is no longer pure.
• The gas jars and the beaker only show where the products go. In industry, Cl₂ and H₂ are piped away.
• Graph: [NaCl(aq)] falls with every Cl₂ made (schematic units). The run stops when the brine gets too dilute. Press R for fresh brine.