Letters: December 2017

I have a question about the action required for a bulging tank of sodium hypochlorite solution in September’s On the spot (Chemistry World, September 2017, p73). The answer given suggests that chlorine could be the cause of the bulging tank and precautions should be taken for a toxic gas. Sodium hypochlorite solution is supplied with an excess of alkalinity and under alkaline conditions it decomposes slowly to sodium chlorate or oxygen. The decomposition to oxygen can be increased by heat or catalysis by some transition metal ions. It seems more likely in this case that the pressurisation in the tank is due to oxygen gas, and the gas can be released by opening the cap.