Question

What is a double indicator titration?

Answer 1

Determination of carbonate and bicarbonate is an example. Use phenolphthalein indicator to titrate to the first end point (determines bicarbonate). The indicator goes from pink to colorless. Then add methyl red and titrate to that end point to determine carbonate. Because the phenolphthalein is colorless at it's end point, it does not interfere with the methyl red indicator.