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What it is. This bromocresol purple indicator is a ready-to-use 0.04% (w/v) aqueous solution, containing 0.4 g of bromocresol purple sodium salt per liter of water, supplied in a 125 mL size. It is prepared for direct use in titrations and pH checks, with no weighing or dissolving required.
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The bromocresol purple pH range. The indicator is yellow below pH 5.2 and purple above pH 6.8, passing through intermediate shades in between. That places its color change in the weakly acidic to near-neutral range, covering endpoints that indicators such as bromocresol green (pH 3.8 to 5.4) and bromophenol blue (pH 3.0 to 4.6) cannot reach.
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Why the sodium salt in water. The sodium salt of bromocresol purple (CAS 62625-30-3) dissolves readily in water, so this indicator needs no alcohol. An aqueous solution is low-odor, non-flammable, and generally classified as non-hazardous, making it well-suited for teaching labs, routine QC, and benches where solvent-based indicators are unwelcome.
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How the color change works. In acidic solution, the dye exists mainly in a yellow form that absorbs blue light. As pH rises through its transition, it converts to a purple sulfonate form with an absorbance maximum near 590 nm. The change is reversible, so the indicator follows pH up or down during a titration.
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Why 0.04%. At 0.04%, a few drops give a clearly visible color without adding enough dye to influence the result. This is the standard working strength for sulfonephthalein indicators in titrations, and the same strength is used for Lab Pro's bromophenol blue indicator, which keeps dropping practices consistent across indicators.
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Reading the endpoint. Because the color passes through intermediate shades between yellow and purple, comparing the titration flask against a reference solution of known pH makes the endpoint easier to judge. Good lighting and a white background behind the flask also help make the shift clearer.
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Where it is used. Analysts use it for acid-base titrations with endpoints near pH 6, quick pH checks of buffers and samples, teaching demonstrations of indicator behavior, and microbiological work where the dye signals acid production in culture media.
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Choosing between related indicators. For lower endpoints, compare Lab Pro's Bromocresol Green Indicator, 0.1% (w/v) and Bromophenol Blue Indicator, 0.04% (w/v). For a concentrated, alcohol-based stock of the same dye, see Bromocresol Purple Indicator 1% (w/w) in Methanol.
Technical Specifications
| Product |
Bromocresol purple indicator solution |
| Active Ingredient |
Bromocresol purple sodium salt |
| CAS Numbers |
62625-30-3 (dye, sodium salt); 7732-18-5 (water) |
| Synonyms |
5',5''-Dibromo-o-cresolsulfonphthalein sodium salt, BCP |
| Formula (dye) |
C21H15Br2NaO5S |
| Molecular Weight (dye) |
562.20 g/mol |
| Concentration |
0.04% (w/v), 0.4 g/L in water |
| Transition Range |
pH 5.2 (yellow) to pH 6.8 (purple) |
| Absorbance Maximum (basic form) |
About 590 nm |
| Melting / Boiling Point |
About 0 °C / 100 °C (aqueous) |
| Odor |
Odorless |
| Package Size |
125 mL |
Applications / Common Uses
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Near-neutral titrations: Marks endpoints that fall between pH 5.2 and 6.8.
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Sample pH checks: Gives a fast visual check of whether a sample is above or below about pH 6.
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Teaching labs: Demonstrates indicator color change with a non-flammable aqueous solution.
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Culture media: Signals acid production by microorganisms.
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Buffer verification: Confirms the approximate pH of prepared buffers in the slightly acidic range.
Storage, Handling & Shipping
Store tightly closed at room temperature, away from direct light and strong oxidizers, which can fade the dye. The dilute aqueous solution carries low hazard, but the dye stains skin and surfaces, so wear gloves and eye protection. Dispense only what you need for each run to avoid contaminating the stock solution with acids or bases.
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Incompatible materials: Strong oxidizers.
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Personal protection: Safety glasses and nitrile gloves to prevent eye contact and staining.
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Spill response: Wipe up with absorbent material and rinse the area with water.
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First aid: Eyes: rinse with water for several minutes. Skin: wash with soap and water.
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GHS signal word: Not classified as hazardous in typical 0.04% aqueous formulations.
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