Sodium hydroxide is manufactured by the electrolysis of brine (NaCl solution). Which gas is produced at the anode?
A. Chlorine
B. Nitrogen
C. Hydrogen
D. Oxygen
Answer: Option A
Solution (By JKExamLibrary)
In chlor-alkali process (electrolysis of concentrated NaCl solution), Cl⁻ ions are oxidized at the anode: 2Cl⁻ → Cl₂(g) + 2e⁻ (chlorine gas). At the cathode, H₂O is reduced: 2H₂O + 2e⁻ → H₂(g) + 2OH⁻, producing hydrogen gas and leaving NaOH in solution. The process uses a diaphragm or membrane cell to keep products separate. Chlorine is used for water treatment and PVC.
Explanation:
Chlor-alkali process: electrolysis of brine gives NaOH (at cathode), Cl₂ (at anode), and H₂ (at cathode). Molten NaCl gives Na and Cl₂, not NaOH.
Explanation:
Endothermic reactions absorb heat from the surroundings. The decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) requires continuous heating to proceed. Burning of gas, respiration, and the reaction of sodium with water are all exothermic reactions that release significant amounts of heat energy to the surroundings.
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