Sciencemadness Discussion Board

Mixing Phenolpthalein problem or not?

CHRIS25 - 11-3-2013 at 08:24

I mixed up 0.1g phenolpthalein dry powder with surgical spirits, label indicates a 90% ethanol and 5% methanol. I used a 50mLs : 50mLs ratio surgical spirit to distilled water. It goes milky white. Is this a problem?

Below are just one example extract from the many that I found about the milky white situation, but it does not make sense, at the least it is certainly not clear as to what is meant here. Thankyou.

(Phenolphthalein indicator is made up in alcohol. If you add phenolphthalein/alcohol indicator solution to water, the water goes CLOUDY. You don't want this to happen. You will therefore need to make a ”phenolphthalein/alcohol indicator + water" mixture (keep adding water until the solution clears):

[Edited on 11-3-2013 by CHRIS25]

elementcollector1 - 11-3-2013 at 08:35

That isn't clear? Add water until the solution stops being cloudy.

Vargouille - 11-3-2013 at 11:47

I'm somewhat skeptical of those instructions, especially since phenolpthalein has limited to almost no solubility in water. I should think that adding more of the alcohol would remove the cloudiness. Can anyone chip in on why adding water would get rid of the cloudiness?

bahamuth - 11-3-2013 at 14:50

Phenolphthalein is supposed to be dissolved in alcohol, not water:alcohol. Adding water will not help you get rid of the cloudiness.

But your solution is perfectly usable, unless the phenolphthalein sediments and you would have to mix it again.

CHRIS25 - 11-3-2013 at 14:53

Quote: Originally posted by elementcollector1  
That isn't clear? Add water until the solution stops being cloudy.


No it's not clear it's stupid. You dissolve it in alchohol, you then need to add water to make up your solution. they say don't add it to water in the first sentence then add water in the second sentence, either way it goes cloudy and they contradict themselves. I know there is logic in here somewhere, but that logic is hidden within the brain of the person who wrote this paragraph. I do not know the ins and outs of why it needs water or whether too much alchohol has any effect on the indicator, no information about this can be found on the internet.