16.9 Concentrated Metal Halides | @everexams study template

⚡ 16.9 CONCENTRATED METAL HALIDES

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If the concentrated aqueous solutions of metal halides are electrolyzed, the hydrogen ions are discharged at the cathode if the metal is present higher than hydrogen in electrochemical series. For example, electrolysis of concentrated aqueous solution of sodium chloride will produce hydrogen gas at the cathode. However, for less reactive metals like copper and silver the metal ions are discharged at the cathode.

At the anode, the halide ions are preferentially discharged due to their higher concentration.

Concentrated Metal Halide Graphite Platinum Anode Cathode Cl₂ H₂ Cl⁻ Na⁺ H⁺
Figure 16.9: Concentrated halide electrolysis – halogen at anode, H₂ or metal at cathode

Reactions

Cathode: 2Mⁿ⁺ + 2e⁻ → 2M (if metal below H)
2H⁺ + 2e⁻ → H₂ (if metal above H)

Anode: 2X⁻ → X₂(g) + 2e⁻ (halogen produced)

KEYNOTE: In concentrated halides, anode always gives halogen (Cl₂, Br₂, I₂) due to high [X⁻].

TRICK: “Above H, H₂ blows; below H, metal glows” – cathode product.

MEMORIZE: NaCl (conc) → H₂ (cathode) + Cl₂ (anode) + NaOH; CuCl₂ (conc) → Cu (cathode) + Cl₂ (anode).

Way to remember anode: “Concentrated X⁻, halogen released; dilute OH⁻, oxygen increased.”

📅 Lesson Planner & Activities

Warm-up (5 min): Recall electrochemical series – name three metals above H and two below H.
Lab activity (15 min): Simulate electrolysis of conc. NaCl using inert electrodes – predict products, then watch video or diagram.
Practice (10 min): Write half-reactions for conc. CuCl₂ and conc. AgBr electrolysis.
Group discussion (10 min): Why does concentration affect anode product? (OH⁻ vs X⁻ discharge).
Exit quiz (5 min): 2 MCQs from the set below – quick check.

Planner tip: Combine with 16.8 to compare dilute vs concentrated.

10 MCQs • concentrated halides

📘 student guidelines

• Concentrated halides → anode product = halogen (Cl₂, Br₂, I₂).
• Cathode: check metal’s position relative to H (use series). Above H → H₂ ; below H → metal.
• Example: conc. NaCl → H₂ (cathode) & Cl₂ (anode). conc. CuCl₂ → Cu (cathode) & Cl₂ (anode).
• Do the activities above to reinforce. Adjust font / theme for comfort.

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