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My drain was clogged and I used an old sodium hydroxide based drain cleaner to free it. The cleaner was quite old and inside it was brownish and monolithic, not a bunch of small white spheres anymore.

The problem is that the compound didn't dissolve in water and now I have a mass of this substance in the drain. I was wondering what made the product brown and hard and what can I do to make it soluble again.

The compound contains: sodium hydroxide, inorganic salts and excipients

Thanks!

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    $\begingroup$ For starters, dissolving in warmer water, stirring etc. can help, in general. $\endgroup$
    – Mithoron
    Commented Feb 13, 2022 at 18:54

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You may have been better off ditching the old stuff and buying new, but if you still have some of the material you can check if a smaller amount is still soluble, both visually and with litmus/pH paper (it probably is still alkaline). Sodium hydroxide exposed to ambient air is likely to pick up carbon dioxide and maybe water of hydration to form a carbonate, which is still soluble but much less so than the original sodium hydroxide. If this is so, then the way to get rid of it is basically enough water and patience. Not sure where the brown color came from but I suspect it's only a minor constutuent.

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    $\begingroup$ Thanks, eventually boiling water did the job, I was just curious of what happened from the chemical point of view. $\endgroup$
    – Bakaburg
    Commented Feb 13, 2022 at 19:10

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