I am often surprised at how even highly educated people can sometimes be fooled by slightly unusual things. In my opinion it's nothing but intellectual laziness. If intellectually lazy people see something that's not in the textbooks they immediately jump to the conclusion that something mystic is going on rather that trying to find out what might have happened.
This is a video I found on Youtube about a "mysterious" reaction which apparently has no explanation. As a person who has learnt quite a bit of Chemistry I tried to figure out what could possibly have happened. My explanation may be slightly off or even completely wrong but I have to start somewhere.
Here's what I think happened. If you look
at the video you'll see that a few drops of liquid is added to the distilled
water before the blue universal indicator is added. Since the Indicator is blue
in alkali that "something" was probably an alkali. I remember that pH indicators are frequently weak acids or weak bases and that only a few drops of alkali was added at to the beaker at the start of the experiment so the
concentration of alkali must be very very low.
The universal indicator solution
is made up of a mixture of several pH indicators, some of them weak acids. From
my experience in doing titrations with I've seen that near the endpoint if you keep
swirling the flask the solution turns clear (using phenolphthalein as an example) but the titration is not quite done yet because once the swirling is stopped the solution turns a very very slight pink. You then have to add one more drop to complete
the titration. I reason that the agitation may may be affecting the reaction to a certain extent (I still haven't figured out how but I will soon.). I think this is a similar situation.
One of the acidic indicators in the Universal Indicator mixture reacts with the miniscule amount of base and neutralizes it. After neutralization, the remaining mixture of indicators take on a yellow colour either because the new ions formed are yellow or because the remaining portion of the Universal Indicator has a yellow colour. The colour will probably return to blue if the stirring is stopped.
I hate to burst the bubble of that aspiring magician (He did look awfully pleased with himself) but sometimes the truth is more important.
One of the acidic indicators in the Universal Indicator mixture reacts with the miniscule amount of base and neutralizes it. After neutralization, the remaining mixture of indicators take on a yellow colour either because the new ions formed are yellow or because the remaining portion of the Universal Indicator has a yellow colour. The colour will probably return to blue if the stirring is stopped.
I hate to burst the bubble of that aspiring magician (He did look awfully pleased with himself) but sometimes the truth is more important.
1 comment:
I have observed the swirling effect too. I have a plausible explanation. The liquid at the center of the flask is more of less still and is the unreacted part while your drop reacted with the swirling part (it could be Bernoulli's theorem or simply because its more likely that if fell somewhere other than the center of the conical flask). On standing, the unreacted part gives in the colour again.
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