Hydroxynaphthol blue is an

azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C−N=N−C l ...

. It is used for determining the endpoint in

complexometric titration Complexometric titration (sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determinat ...

s/Metal Titration.

References

Azo dyes Naphthalenesulfonates Organic sodium salts 2-Naphthols {{OrganicAcid-stub