Eriochrome Black T ACS reagent, ≥99.0%

Formula: C 20 H 12 N 3 O 7 SNa Molar mass: 461,381 g/mol Appearance: dark red/brown powder Acidity (pKa): 6.2, 11.55 UN number: 2923 Eriochrome Black T is a complexometric indicator commonly employed in tests for water hardness, particularly during EDTA titrations. It transitions from wine-red to blue as it binds and subsequently releases metal ions such as calcium and magnesium, facilitating the determination of their concentration in a solution.