fusso
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Optimum indicator concentration?
I want to prepare EtOH solns of phenolphthalein and methyl orange. What's the optimum concentration? Too dilute will make colour too pale and need
many drops and waste EtOH. Too concentrated will make every titration consume too much precious indicator even only 1 drop. Thx.
Disclaimer: I'm a minimalist
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j_sum1
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https://www.google.com.au/search?q=preparation+of+phenolphth...
I think you could have done this yourself.
Practically, you are hard-pushed to purchase phenolphthalein in quantities less than 5g, and that much can last years. Minimalist or no, indicators
are not a big expense.
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DavidJR
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Yeah, pre-made indicator solutions always feel like a total ripoff (cough says the person selling premixed bromocresol purple solution on eBay) but
making your own is super cheap. I bought 25g of phenolphthalein for £3.60 (from betterequipped.co.uk). At 0.5% w/v this would make 5 litres of
solution, which frankly is a lifetime supply for me.
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fusso
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I did search about it, so I dunno whether I should use 0.5% or Nilered's 0.05% or even more dilute.
And you didn't mention methyl orange.
Also is substituting EtOH with i-PrOH ok?
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aga
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Everything is fine. It's all OK. Calm. Think happy thoughts.
The exact concentration only ever matters if you need to use it, even then, not so much.
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LearnedAmateur
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At school our phenolphthalein was always 1% w/v in ethanol, prepped on site. Not sure on the methyl orange and bromothymol blue though, but most
likely between 0.5 and 2%.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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DavidJR
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I'd just go with 0.5% for phenolphthalein and be done with it. Isopropanol will work fine.
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