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Topic: Methyl blue colour in basic region  (Read 1511 times)

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Offline heronne

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Methyl blue colour in basic region
« on: April 01, 2016, 03:03:28 AM »
Hello, I am doing a work on erasable blue ink. By doing some research I have found that one of the ingredients might be methyl blue. To test that, I have added sodium hydroxide and hydrochloric acid to it and observed the colour change. By designing an experiment in which I mixed ink with sodium hydroxide and added drops of water I found the colour change to occur between pH values of 11.9 and 12.9, which does fit in the pH range I have found on various websites. However in solutions with a pH over 12.9 I observed the colour red instead of the predicted pale-violet (http://www2.ucdsb.on.ca/tiss/stretton/Database/indicators.htm). I cannot find anything to explain that difference in colour. Could anyone please tell me if I am on the right track and/or share some information with me? Thanks in advance.

Offline Intanjir

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Re: Methyl blue colour in basic region
« Reply #1 on: April 01, 2016, 01:38:26 PM »
If you dilute it at the same pH does it resemble pink or does it resemble pale violet?

I don't think you can really trust the precise sense of color of those charts that are out there, particularly for an uncommon indicator. Whether it turned pink rather than violet might not have been a clear enough distinction to have been noticed. Particularly since they list it as 'pale' suggesting that they didn't use enough indicator to clearly make out it's color at that pH.

Offline heronne

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Re: Methyl blue colour in basic region
« Reply #2 on: April 04, 2016, 04:38:07 AM »
Thanks for your reply, it was very useful.
The solution does look pink when diluted but it is true the distinction is unclear. That is likely to be the explanation.

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