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Due to a color change from blue to red at pH 3.0–5.2, Congo red can be used as a pH indicator.Since this color change is an approximate inverse of that of litmus, it can be used with litmus paper in a simple parlor trick: add a drop or two of Congo red to both an acid solution and a base solution.
A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. [1] Hence, a pH indicator is a chemical detector for hydronium ions (H 3 O +) or hydrogen ions (H +) in the ...
Transition interval (pH range) Color after high pH conditions Methyl Orange Orange/red 3.1 - 4.4 Yellow Methyl Red Red 4.4 - 6.3 Yellow Congo Red Blue 3.0 - 5.2 Red Phenolphthalein Colourless 8.3 - 10.0 Pink Thymolphthalein Colourless 9.3 - 10.5 Blue Bromophenol Blue Yellow 3.0 - 4.6 Blue Bromocresol Green Yellow 3.8 - 5.6 Blue Thymol Blue Red
Phenol red, 40 μM: colors in cell culture medium at a pH range from 6.0 to 8.0. Most living tissues prosper at a near-neutral pH—that is, a pH close to 7. The pH of blood ranges from 7.35 to 7.45, for instance.
Low pH colour Transition pH range High pH colour Thymol blue (first transition) Red 1.2 – 2.8 Yellow Methyl orange: Red 3.2 – 4.4 Yellow Methyl red: Red 4.8 – 6.0 Yellow Bromothymol blue: Yellow 6.0 – 7.6 Blue Thymol blue (second transition) Yellow 8.0 – 9.6 Blue Phenolphthalein: Colourless 8.3 – 10.0 Fuchsia
It is advised to check the references for photos of reaction results. [1] Reagent testers might show the colour of the desired substance while not showing a different colour for a more dangerous additive. [2]
Cresol red can also be used as an electrophoretic color marker to monitor the process of agarose gel electrophoresis and polyacrylamide gel electrophoresis.In a 1% agarose gel, it runs approximately at the size of a 125 base pair (bp) DNA molecule (it depends on the concentration of buffer and other component).
The pH range is commonly given as zero to 14, but a pH value can be less than 0 for very concentrated strong acids or greater than 14 for very concentrated strong bases. [2] The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. [3]