The indicator phenolphthalein is used in the titration of NaOH and H2SO4. Phenolphthalein turns bright pink when the titration is complete and the sulfuric acid is neutralized.
Acid-base titration is a process that scientists utilize to neutralize an acid in order to determine the acid's concentration. In the titration of NaOH and H2SO4, an unknown concentration of H2SO4 is added to a flask. Next, NaOH is added to the H2SO4 by drops. NaOH dissociates into Na+ and OH-, while H2SO4 dissociates into H+ and HSO4-. Once the number of OH- ions equals the number of H+ ions, the acid is neutralized and the indicator, phenolphthalein, turns bright pink.