Kagutsuchi
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Indicaor problems
I used fenolftaleine to see when my KOH solution becomes neutralised by HCl, but when I added it to the very-very concentrated KOH and the
fenolftaleine gave no color at all! What could have possibly caused it? Also, if someone has a paper on a broad number of indcators, I'd be happy if
he shared it with me.
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blogfast25
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Quote: Originally posted by Kagutsuchi  | | I used fenolftaleine to see when my KOH solution becomes neutralised by HCl, but when I added it to the very-very concentrated KOH and the
fenolftaleine gave no color at all! What could have possibly caused it? Also, if someone has a paper on a broad number of indcators, I'd be happy if
he shared it with me. |
It's normal: above pH 13 that indicator is colourless:
https://en.wikipedia.org/?title=Phenolphthalein#Indicator
Start neutralising and the fuchsia will appear. Then continue adding HCl until it disappears.
But neutralising very concentrated KOH solutions can be dangerous: very considerable (neutralisation) heat is evolved, even more so when the
solubility limit of KCl is exceeded and solid KCl forms: the dissolution of KCl is endothermic, so the precipitation is exothermic. Splattering of a
highly caustic solution is a real concern, trust me: first hand experience!  Slow
addition of HCl with intermittent cooling is strongly advisable!
[Edited on 26-6-2015 by blogfast25]
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