mycotheologist
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Using methylene blue as an indicator for the haloform reaction
So if I can recall correctly, methylene blue changes colour depending on the oxidation state of the compounds in the solution. The compound appears
blue in an oxidising environment and colourless in a reducing environment. So if you were to add a few drops of methylene blue to a beaker of
household bleach, it will turn blue in due to the presence of the highly oxidising NaClO. Adding acetone to the solution, a highly exothermic reaction
between the acetone and hypochlorite ion ensues:
CH3COCH3 + 3NaOCl -----> CHCl3 + 2NaOH + Na(CH3COO)
NaOH is a reasonable reducing agent, isn't it? If so, the problem here will be that the colour change won't indicate a complete reaction, rather it
will indicate a half reaction because it will go colourless when the amount of NaOH becomes greater than the amount of NaClO. Any ideas on how I could
prevent the NaOH from interfering? Its the chloroform I'm after so I will distil the product and thus, am not worried about forming non volatile
byproducts.
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bbartlog
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| Quote: | | NaOH is a reasonable reducing agent, isn't it? |
No. Also from what I recall the reaction doesn't run 100% to completion.... and why do you feel like you need an endpoint indicator anyway? You can if
you like use a thermometer and see when the temperature starts dropping again - that's a pretty good sign you're done.
The less you bet, the more you lose when you win.
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mycotheologist
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What I had in mind was using an end point indicator to avoid the need to calculate the exact amount of reagents beforehand. For example, when making
sodium acetate from vinegar, instead of calculating the moles of CH3COOH in the volume of vinegar, then calculating and weighing an equal number of
moles of NaOH, its a lot quicker and easier to just add a few drops of phenolphthalein to the vinegar then gradually add solid NaOH, with stirring,
until the solution turns pink.
[Edited on 18-3-2012 by mycotheologist]
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mycotheologist
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I'm really just looking for an excuse to use some of this methylene blue I've had lying around for months now.
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zoombafu
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Extract some DNA and stain it, a dark blue DNA clump looks really beautiful suspended in clear ethanol.
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