Bromothymol blue

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Bromothymol blue

Systematic name
Chemical formula	C₂₇H₂₈Br₂O₅S
Molecular mass	624.39
Density	x.xxx g/cm³
Melting point	xx.x °C
Boiling point	xx.x °C
CAS number	[76-59-5]
SMILES	xxxxx
Disclaimer and references

Bromothymol blue (pH indicator)
below pH 6.0		above pH 7.6
6.0	↔	7.6

Bromothymol blue (alt: dibromothymolsulfonephthalein, bromthymol blue, BTB) is a chemical indicator for weak acids and bases.

The bromothymol blue acts as a weak acid in solution and therefore can be in acid or base forms which appear yellow and blue respectively. It is green in neutral solution. Bromothymol blue is typically sold in solid form as the sodium salt of the acid indicator. It also finds occasional use in the laboratory as a biological slide stain. At this point it is already blue, and a drop or two is used on a water slide. The cover slip is placed on top of the water droplet and the specimen in it, with the blue coloring mixed in. It is sometimes used to define cell walls or nuclei under the microscope.

Bromothymol blue is mostly used in measuring substances that would have relatively low acidic or basic levels (near a neutral pH). It's often used in pools, fish tanks, or measuring the presence of carbonic acid in a liquid.

C₂₇H₂₈Br₂O₅S ↔ H⁺ + C₂₇H₂₇Br₂O₅S^-

The pKa for bromothymol blue is 7.10.