Iam using photocatalyst for photodegrade phenolphethalien in alkaline medium but the fading of phenolphethalien color with time cause aproblem in monitoring %R making me not know this percent due to fading or degradation I had tried for more times but the PH decrease and the color fading with time
when i add soda after the reaction the solution turned to pink
please any one can help me in this problem?
Hi Khaled Hassan
Phenolphthalein is a pH indicator and in the alkaline medium, it shows color. For the photodegradation process, the solution pH is an important parameter as the surface charge of the photocatalyst is influenced. Please check the pHZPC of the photocatalyst you are using.
Regards
Hi @Arnab Mukherjee
thank you
but when I prepared a phenolphethalien alkaline solution without adding the catalyst and left it for a while the color was disappeared.
Hi @Arnab Mukherjee
thank you
but when I prepared a phenolphethalien alkaline solution without adding the catalyst and left it for a while the color was disappeared.
Hi Khaled Hassan
Phenolphthalein is a common acid-base indicator used to determine the endpoint in acid-base titrations. It is also the active ingredient in some laxatives. If excess base is present at the end of an acid-base titration, the pink phenolphthalein color fades if the solution is allowed to stand for a while.
The structure of the colorless form of phenolphthalein is C20H14O4. At a pH of 8 or lower, the structure will be abbreviated as H2P and in the pH range of 8-10 both acidic protons are rapidly removed from the colorless H2P by NaOH, (OH - ) to give the pink P2- ion according to the equation:
H2P+2OH-=P2-+2H2O(pink)
At a pH above 10 the pink color slowly fades as P2- reacts further with NaOH, (OH - ), to give the colorless POH3- ion:
P2-+OH-=POH3-(colorless)
For decolorization, pH is a major factor. I can say the above from my side.
Regards
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts