======Electrolysis of Sodium Chloride (Brine)======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Electrolysis of Aqueous NaCl
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====Summary====                   
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====Procedure====  
  - Prepare a brine electrolyte (e.g., ~3–10% w/v NaCl in water). Pour into an electrolysis cell or beaker to near the top.
  - Insert two inert electrodes (carbon/graphite or platinum) through a stopper or clamp so they do not touch. Connect to a low-voltage DC supply (≈6–12 V) with the ammeter in series.
  - Fill two small test tubes with brine, cover their mouths, invert them over each electrode (still filled) to collect gases by displacement.
  - Switch on the power and adjust current to a steady few hundred mA to a few A for a class demo. Observe bubbles: more at the cathode (H₂) and at the anode (Cl₂).
  - When enough gas is collected, close the taps (or keep tubes inverted) and test:
    - Cathode tube: bring a lit splint to the mouth—expect a squeaky pop (hydrogen).
    - Anode tube: hold damp blue litmus near the mouth—expect it to redden then bleach (chlorine). Do not sniff directly.
  - Sample the bulk solution and add a drop of universal indicator—expect green → blue/purple, showing sodium hydroxide formation.
  - (Optional) Continue longer with very dilute brine to observe some oxygen at the anode (less common initially).



====Links==== 
Electrolysis of brine using carbon fibre electrodes part 1 MVI 6014 - Nigel Baldwin: 
{{youtube>AmlwCyKhwG0?}}\\


📄 ELECTROLYSIS of aqueous SODIUM CHLORIDE SOLUTION and sodium bromide and potassium iodide solutions NaCl(aq), NaBr(aq) and KI(aq) - Doc Brown: [[https://www.docbrown.info/page01/ExIndChem/electrochemistry03.htm]]\\

====Variations====
  * Use a Hofmann voltammeter to measure gas volumes and compare H₂:Cl₂ (theoretical 1:1; observed Cl₂ may be lower due to solubility/side reactions).
  * Compare concentrated vs. very dilute brine to discuss when O₂ competes with Cl₂ at the anode.
  * Swap carbon for platinum electrodes and compare stability/observations.
  * Collect chlorine into a trap leading to dilute NaOH to form bleach (NaOCl), then test with iodide–starch paper (teacher demo only).



====Safety Precautions====
  * Wear splash goggles, gloves, and a lab coat; work with good ventilation or a fume hood—chlorine is toxic and irritating.
  * Keep current modest; do not scale up gas volumes. Use only small tubes for collection.
  * Never inhale gases; test chlorine indirectly (indicator paper) rather than smelling.
  * Keep electrodes from touching to avoid short circuits; dry hands before handling power leads.
  * Neutralize/chlorine-scrub anode off-gas if running for extended times (e.g., through dilute NaOH). Dispose solutions according to local rules.
  * Do not ignite gases directly at the anode outlet; perform ignition tests only on small, collected samples away from the cell.




====Questions to Consider====
  * What half-reactions occur at each electrode?
  * What is the overall reaction in brine electrolysis?
  * Why is hydrogen produced instead of sodium metal in aqueous solution? (Na⁺ reduction is unfavorable in water; water is reduced to H₂.)
  * Why might the measured volume of chlorine be less than hydrogen? (Cl₂ dissolves/reacts with formed NaOH; some hydrolysis.)
  * How does dilution affect anode products? (At low [Cl⁻], OH⁻/H₂O oxidation can produce O₂, increasing O₂:Cl₂ over time.)
  * How can you confirm NaOH formation in the electrolyte? (Indicator turns blue/purple; pH measurement shows alkaline.)