Bromocresol purple

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Bromocresol purple
Structure of Bromocresol purple.png
CAS number 115-40-2 YesY
PubChem 8273
ChemSpider 7974 YesY
Jmol-3D images Image 1
Molecular formula C21H16Br2O5S
Molar mass 540.22 g mol−1
Appearance Purple powder
Melting point 241 to 242 °C (466 to 468 °F; 514 to 515 K) (decomposition)
Solubility in water < 0.1 %
R-phrases R36/37/38
S-phrases S26, S36
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Bromocresol purple (BCP) or 5',5"-dibromo-o-cresolsulfophthalein, is a pH indicator. In its sultone form, it has a pKa value of 6.3,[1] and is usually prepared as a 0.04% aqueous solution.

Bromocresol purple (pH indicator)
below pH 5.2 above pH 6.8
5.2 6.8


Besides its primary function as an indicator, bromocresol purple is used in medical laboratories to measure albumin, and as an addition to acid stop baths used in photographic processing as an indicator that the bath has reached neutral pH and needs to be replaced.


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