when we add Phenophlein to NaoH , it shows pink color. Why?
2006-11-20 04:53:33 · 3 answers · asked by haris 1 in Science & Mathematics ➔ Chemistry
At high pH values (>10), the Hydroxide ion in solution takes protons from the phenolphthalein indicator, forming an ion and water. The -2 ionic form of phenolphthalein then rearranges the electronic structure to form the characteristic pink color.
See the wikipedia article for more.
2006-11-20 04:58:10 · answer #1 · answered by Dave_Stark 7 · 1⤊ 0⤋
The OH pulls off a proton to give a quinone type structure these generally absorb visible light very strongly.
If the solution is left the colour will fade as another H+ is pulled off forming a colourless form. So thats why it is the first pink colouration that is taken to be the end point.
2006-11-20 13:32:31 · answer #2 · answered by deflagrated 4 · 0⤊ 0⤋
The name is "phenolphtalein". This substance is used in solutions as an indicator (which changes color according to pH).
It's formula is C20H14O4. It's quite a complex structure. But the important part is that it has two phenolic -OH groups. In basic solutions these groups lose a proton each and the compund turns pink.
2006-11-20 13:04:41 · answer #3 · answered by Ferts 3 · 1⤊ 0⤋