“Does Chlorine react with Acid?”

A question which I was once asked was, “Does chlorine react with acid?” And when I gave a quick answer to this question, I assumed that when the person asking it said “Chlorine”, he meant Cl2 gas. What I had forgotten was, that some people, including the person who was asking this question, take the word “Chlorine” to be a synonym for ‘Chlorine Bleach’. And of course, chlorine bleach reacts with acid! But to understand how such communication errors take place, one must actually understand, ‘What is chlorine bleach?’

Most preparations of chlorine bleach, are based on either sodium hypochlorite (NaOCl), or potassium hypochlorite (KOCl), with a generous amount of the corresponding hydroxide added to it, to stabilize it. This modern mixture is prepared industrially, by allowing chlorine gas to react with sodium hydroxide solution, for the sake of argument, which generates a mixture of sodium chloride – i.e., salt – and sodium hypochlorite:

Cl2(g) + 2NaOH(aq) -> NaCl + NaOCl + H2O

What happens next is that Engineering separates the (useful) sodium hypochlorite from the (useless) sodium chloride, and adds more sodium hydroxide to it, to arrive at the final mixture.

The treacherous fact about this sort of mixture is, that the reaction that produced it is readily reversible. Sodium hypochlorite solutions will react under any of the following conditions, to cause dangerous gasses, such as Cl2, but not only Cl2 to be generated, where Cl2 is also a gas that was used in Chemical Warfare, in WW1:

  • When mixed with anything that would neutralize the sodium hydroxide, including any acid,
  • When mixed with so-called reducing agents, such as ammonia,
  • When mixed with salt,
  • In fact, sodium hypochlorite solutions are not 100% stable, when neutral…
  • Etc., etc., etc..

But just to be clear, if one starts with the deadly gas that is Cl2, No, that does not react readily with common acids.

(Update 5/06/2020, 15h15 … )

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