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Fumaric acid has pK a values of approximately 3.0 and 4.5. By contrast, maleic acid has p K a values of approximately 1.5 and 6.5. The reason for this large difference is that when one proton is removed from the cis isomer (maleic acid) a strong intramolecular hydrogen bond is formed with the nearby remaining carboxyl group.
Fumaric acid or trans-butenedioic acid is an organic compound with the formula HO 2 CCH=CHCO 2 H. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. [3] The salts and esters are known as fumarates. Fumarate can also refer to the C 4 H 2 O 2− 4 ion (in ...
Example Bjerrum plot: Change in carbonate system of seawater from ocean acidification.. A Bjerrum plot (named after Niels Bjerrum), sometimes also known as a Sillén diagram (after Lars Gunnar Sillén), or a Hägg diagram (after Gunnar Hägg) [1] is a graph of the concentrations of the different species of a polyprotic acid in a solution, as a function of pH, [2] when the solution is at ...
These compounds are weak dibasic acids with pK a tending towards values of ca. 4.5 and 5.5 as the separation between the two carboxylate groups increases. Thus, in an aqueous solution at pH about 7, typical of biological systems, the Henderson–Hasselbalch equation indicates they exist predominantly as dicarboxylate anions.
Cotinine has an in vivo half-life of approximately 20 hours, and is typically detectable for several days (up to one week) after the use of tobacco. The level of cotinine in the blood, saliva, and urine is proportionate to the amount of exposure to tobacco smoke, so it is a valuable indicator of tobacco smoke exposure, including secondary (passive) smoke. [14]
Maleic acid has a heat of combustion of -1,355 kJ/mol., [6] 22.7 kJ/mol higher than that of fumaric acid. Maleic acid is more soluble in water than fumaric acid. The melting point of maleic acid (135 °C) is also much lower than that of fumaric acid (287 °C). As confirmed by X-ray crystallography, maleic acid is planar.
When the difference between successive pK a values is less than about 3, there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. In the case of citric acid, the overlap is extensive and solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.
The values below are standard apparent reduction potentials (E°') for electro-biochemical half-reactions measured at 25 °C, 1 atmosphere and a pH of 7 in aqueous solution. [ 1 ] [ 2 ] The actual physiological potential depends on the ratio of the reduced ( Red ) and oxidized ( Ox ) forms according to the Nernst equation and the thermal voltage .