Sodium hypochlorite is usually purchased at 12% to 12.5% and is then distributed down to a more stable percentage of ______.

• A. 8%
• B. 4%
• C. 5%
• D. 6%

Answer: (D)

Sodium hypochlorite is unstable and decomposes more quickly at higher concentrations, especially when exposed to heat, light, or metals. Diluting the stock solution from about 12% to a lower, common distribution level makes it easier to store, handle, and feed into chlorine dosing systems, while also slowing the rate of chlorine loss. A 6% solution hits a practical balance: it remains relatively stable in storage and transport, yet is strong enough to provide effective disinfection when dosed correctly. That’s why 6% is the standard distribution concentration. Higher concentrations would decompose faster and be harder to manage, while much lower concentrations would require larger volumes to achieve the same disinfection, making 6% the most convenient and reliable choice in many plants.