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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.
Conversely, if a 10-fold excess of the acid occurs with respect to the base, the ratio is 1:10 and the pH is pK a − 1 or pK b − 1. For optimal accuracy, the color difference between the two species should be as clear as possible, and the narrower the pH range of the color change the better.
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 ]
A universal indicator is a pH indicator made of a solution of several compounds that exhibit various smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. A universal indicator can be in paper form or present in a form of a solution. [1]
Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pK a of 5.1. [2]
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. When cells are grown in tissue culture, the medium in which they grow is held close to this physiological pH. A small amount of phenol red added to this growth medium will have a pink-red color under normal ...
Chlorophenol red is an indicator dye that changes color from yellow to violet in the pH range 5.4 to 6.8. [2] The pH of a substance is determined by taking the negative logarithm of the Hydronium ion concentration and the indictor changes color due to the dissociation of H + ions. [3] The lambda max is at 572 nm. [4]
If the carbon dioxide content is lower than 0.04%, it changes from red to magenta and, in relatively very low carbon dioxide concentrations, to purple. [1] Carbon dioxide, even in the concentrations found in exhaled air, will dissolve in the indicator to form carbonic acid , a weak acid , which will lower the pH and give the characteristic ...