Eriochrome black T is widely used as a pH indicator and complexometric indicator in analytical chemistry. It is particularly valuable in the titration of metal ions, especially calcium and magnesium, in water hardness testing. When added to a solution, it forms colored complexes with these metal ions, allowing for precise endpoint detection during titration with EDTA. Its distinct color change from red to blue at the endpoint makes it a reliable tool for determining the concentration of metal ions in various samples. Additionally, it is employed in educational laboratories to teach students about complexometric titrations and water quality analysis.