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It is a weak acid with pK a = 8.00 at 20 °C (68 °F). A solution of phenol red is used as a pH indicator, often in cell culture. Its color exhibits a gradual transition from yellow (λ max = 443 nm [2]) to red (λ max = 570 nm [3]) over the pH range 6.8 to 8.2. Above pH 8.2, phenol red turns a bright pink color. [4] [5]
The spectra of basic, acid and intermediate pH solutions are shown. The analytical concentration of the dye is the same in all solutions. In spectroscopy, an isosbestic point is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample ...
pH indicators: a graphic view. 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]
amino acid zwitterions 1550–1610 O─H alcohols, phenols: low concentration 3610–3670 high concentration 3200–3400 broad carboxylic acids low concentration 3500–3560 high concentration 3000 broad N─H primary amines: any 3400–3500 strong 1560–1640 strong secondary amines any >3000 weak to medium ammonium ions any 2400–3200
The simplest is phenol, C 6 H 5 OH. Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule. Phenol – the simplest of the phenols Chemical structure of salicylic acid, the active metabolite of aspirin. Phenols are both synthesized industrially and produced by plants and ...
It is often said the resonance stability of phenol makes it a stronger acid than that of aliphatic alcohols such as ethanol (pK a = 10 vs. 16–18). However, a significant contribution is the greater electronegativity of the sp 2 alpha carbon in phenol compared to the sp 3 alpha carbon in aliphatic alcohols. [7]
It is a weak acid, which can lose H + ions in solution. The nonionized phenolphthalein molecule is colorless and the double deprotonated phenolphthalein ion is fuchsia. Further proton loss in higher pH occurs slowly and leads to a colorless form. Phenolphthalein ion in concentrated sulfuric acid is orange red due to sulfonation. [2]
The phenolic unit can be found dimerized or further polymerized, creating a new class of polyphenol. For example, ellagic acid is a dimer of gallic acid and forms the class of ellagitannins, or a catechin and a gallocatechin can combine to form the red compound theaflavin, a process that also results in the large class of brown thearubigins in tea.