Question: what is the difference between phenolphthalein alkalinity and total alkalinity?
Answer: Phenolphthalein alkalinity measures the hydroxides and half the carbonates at a pH 8.3. Total alkalinity measures all carbonate, bicarbonate, and hydroxide alkalinity at a pH 4.5 (approximately). ... Therefore the phenolphthalein alkalinity would equal the total alkalinity and all of it would be hydroxide.