How does Phenolphthalein change its’ color? It is an acid base indicator Colorless in acidic medium and magenta/pink in alkaline solution The structures of the molecule in both media are given. Both of the structures absorb light in UV region but only the one in right is absorbed in visible region at around 553nm. For UV absorption, the changes cannot detect by our naked eye, however the absorption at 553nm is detected. 553nm belonged to green region of visible spectrum, so it’s complimentary color magenta is seen. As the shift of absorption to higher wavelength which is a bathochromic shift is associated with a greater degree of delocalization, lowers the energy gap between HOMO and LUMO. It needs less energy to make the electron jump and a longer wavelength of light is absorbed.
Posted on: Tue, 02 Sep 2014 13:27:57 +0000
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