Australia's Science Forum

Hi All,
Here is a general question for you...
I have 3 bottles of universal indicator in my cupboard. They are three different colours. Is this normal? One is green (neutral), one is yellow and another is a yellow-green colour. I just went to refill our dropper bottles which currently contain yellow universal indicator. I would assume it should be green as that is the neutral colour. Will the other colours still work or should I throw them out?
Rosalie

Try adding a few drops of 0.05M Sodium Hydroxide untill the mixture returns to green. Some times it works fine, other times it will not return to green.

Good luck
Regards

Hi RosalieM,

I tip out the contaminated solution. I keep the universal indicator in dropper bottles, but only fill them halfway or less because some of them come back contaminated. My theory is that the students put the dropper itself into the beaker of solution instead of dropping the indicator from the dropper into the solution - if that makes sense.

Hi there RosalieM
To bring back the green (neutral) of Universal Indicator, I mix a weak solution of Sodium Bicarbonate or Boric Acid with distilled water and then add it drop by drop until the green colour is reached.It may only take a couple of drops!!! Joh has the right idea
Cheers
Mother