Bromothymol blue

The blue bromothymol (or BBT, or dibromothymolsulfonephthaléine) are a chemical Composé often used like indicator of pH. Indeed, it has properties halochromic S.

Structures

August 1st The bromothymol blue is one of the principal compounds of the family of the indicator pH which derive from the Triphénylméthane.

Model 3D of the molecule of the bromothymol Blue

Colors of the bromothymol blue

The form Acide is Jaune (pH<6,0) and forms it basic is Bleu E (pH>7,6). Between these two pH, a solution containing this compound is of color Vert E (mixture of both colors). Following the example Blue thymol , the bromothymol blue has also a second zone of turn, but in concentrated acid medium (pH<0), it transfers then Jaune with the fuchsia when the pH decreases.

; Caption image :

  • Tube 2: form Acide (yellow) bromothymol blue (chlorydric acid solution to 0,5 mol/L)

  • Tube 4: form basic (blue) bromothymol blue (solution of sodium hydroxide with 1 mol/L)

  • Tube 3: zone of turn of the bromothymol blue (coexistence of the forms acid and basic)

  • Tube 1: form superacide blue of bromothymol (hydrochloric acid concentrate, negative pH)

Uses

The halochromic properties of the bromothymol blue are used in particular to follow the changes of pH during the acido-basic proportionings. Its zone of turn including/understanding the neutral pH, they are proportionings between acids and strong bases which require an indicator such as the BBT, the equivalent point being located at a pH of 7.

In general, the particular zone of turn of the BBT makes it possible to indicate quickly if a solution is acid or basic. This compound makes it possible to detect the presence of Carbon dioxide, which is an acid, by change of color of blue with yellow of the crystals.

The bromothymol blue is in addition also used like Pigment for the Teinture.

Appendices

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