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Is it plausible that free chlorine could be formed in concentrated hydrochloric acid.

The background to this is that I have bought some 30% HCl to remove calcium carbonate scale from a reverse osmosis water purifier. The latest batch of HCl seems to have a very slight yellowish tint which I had not noticed on previous occasions. Having used some of this acid I find that the performance of the membrane seems to have deteriorated (these membranes are notably sensitive to hypochlorite).

Could some factor (perhaps exposure to direct sunlight) be responsible?

Is there a way that I could detect the presence of dissolved chlorine?

Can anyone suggest an alternative explanation?

Thanks, Chris.

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You could buy the chlorine test strips from a pool supply store to test for hypochlorite. You may need to neutralize the acid before testing, so ask if the test is accurate in a strong acidic solution.

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The color could be due to other impurities, such as iron. That might also be harsh on delicate RO membranes, perhaps by precipitating a floc on the membrane.

If it is iron, neutralizing with clear alkali (NaOH or KOH) to pH 6-7 would precipitate a floc. This floc might be more difficult to see than the off-color, so try a Tyndall test. Take a flashlight with a very narrow beam of white light and shine it thru the neutralized solution. If the beam lights up like a beam of light in a smoke-filled room, you have a precipitate. There are inexpensive LED flashlights that are perfect for this. Red lasers might not show the scattered beam as well.

I have to warn you - after you see the Tyndall effect in an otherwise clear solution, you'll want to test everything you come across!

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