What is happening to the [OH-] when the solution turns from pink to violet?

the hydroxide ions are undergoing ionization and the particles are gaining / losing electrons .

Explanation:

i think it is because ::

the phenolphthalein of the solution has gone from having a pH of around 8 (pink) to being alkaline at above 10 which causes it to burn purple / violet .

imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.