Bromothymol blue

[Wato]

Hi Everyone,

I'm after some wisdom.....we have a batch of Bromothymol blue made up and instead of turning yellow in an acid we are getting a beautiful pink colour.....any suggestions?????

Thanks Donna

[Xenon]

Hi Donna

The acid is too strong. Adjust to pH 6 (only slightly acidic) and should go yellow.

Xe, SD, KOPR

[Wato]

Hi Xenon,
Thanks for the response but the HCl acid is made up to 0.5M for a titration assessment for year 12. I can't dilute the acid. It is also reacting funny with alkalis and neutrals.

Any other suggestions

Donna

[ri]

Hi Donna,
I wonder if you have some contamination from phenolphthalein?
We have found that this indicator is notoriously hard to rinse out of dropper bottles, especially the rubber droppers assembly - the end points seems to be about the same....
Good luck,
~Robyn

[Mother]

Hi Donna
This may get you out of trouble:

BROMOTHYMOL BLUE

Use: Indicator is especially useful for detection of carbon dioxide in solution(turns yellow) in photosynthesis and respiration experiments.

Preparation: 0.1g of Bromothymol Blue powder in 1 Litre of distilled water.If solution appears green,add 0.1M of NaOH one drop at a time until blue colour is obtained.PH range should be about 6.0 to 7.6
Also if the blue colour has disappeared just carefully add some drops of NaOH until the blue colour has returned.
Cheers
Mother

[Robb]

Hi Donna, All,

Bromothymol Blue (DIBROMOTHYMOLSULFONEPHTHALEIN) should be Green when purchased or Prepared. The Bromothymol Blue comes from the name it has when exposed to Alkalia pH ranges from 7.8 - Lower(7.8 - 14)Havin a unique Brilliant Blue colour. When exposed to pH values of 7.2 or Higher (7.2 - 0) the colour will be yellow.

The colour change you are getting suggests to me that The Bromothymol Blue may be contaminated with possibly Methyl Red.

Why I say Methyl Red apposed to the Phenolphthalein that others suggest, is that you are using an acid, and the change of pink in Phenolphthalein requires alkaline conditions. If the solution you are using is HCl then there must be a little Methyl Red present somewhere. Hence a pink discolouration is present (This would be a light pink discolourisation).

What you could have done was still used the solution and had the colour change of the Bromothymol Blue change to yellow first then soon after that the Red would of been apparent. hence without having any effect on results. (But one would have to be consious as to where the change is though).

I hope this makes sense of an old question,

Cheers,

Robb.....

[Ocker]

I have a chart I find most helpful tried to scan it and insert in here but don't think it worked, anyway worth the try

[Robb]

Hi Ocker,

Everything's certainly worth a try,

Cheers,

Robb.....

[Ocker]

OK Robb
Your the Genius, I don't have time to play
How do you go about putting scanded image in here as a post
Maybe this is in the wrong place!
but "all knowledge is good"