Australia's Science Forum

Hi All, looking for some info, I couldn't find phenol red solution to purchase so had to buy as powder. Do any of you have any tried and tested recipes for making it up into solution. I only need small amounts for the disease prac. Ta muchly MariaC

The recipe I have says to dissolve 0.2g in 200ml ethanol and make up to 1L with distilled water. You could probably halve it and put it into 10 dropper bottles and you'll have enough for several years You'll never need to buy the solution again!

Hi
I found via google this website http://www.chemistry-infolab.com/ph_indicators.html
It has recipes for making most indicators.

Phenol red
Dissolve 0.1g. in 100 ml. of 20% ethanol, or dissolve 0.04g in 1.13 ml of 0.1M sodium hydroxide and make up to 100 ml.
pH =6.4 - 8.2; color change = yellow to red-violet


Have you had any problems with the Phenol Red method made to one litre. I need this indicator on Monday.

Thanks

I have the same recipe as Rosalie M and it says pH6.8 to 8.4 yellow-red.

The recipe I have is 0.5g dissolved in 500ml distilled water.

I'm just looking through my "Manual for School Assistants Working in Science".
It has a chart for preparing acid/base indicators which uses 0.2g phenol red per litre 20% ethanol.
This changes from yellow to red indicating pH 6.8-8.4.

In the section "Reagents and Stains Used in Biology' it uses 0.5g phenol red in 500mL distilled water as an indicator for carbon dioxide in solution.
This turns yellow in acidic solutions, indicator range pH 0.0-2.0

So it would appear that the method of preparation depends on the use.