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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. Calculation of the pH with a polyprotic acid requires a speciation calculation to be performed. In the case of citric acid, this entails the solution of the two equations of mass balance:
Citric acid is a triprotic acid, with pK a values, extrapolated to zero ionic strength, of 3.128, 4.761, and 6.396 at 25 °C. [21] The pK a of the hydroxyl group has been found, by means of 13 C NMR spectroscopy, to be 14.4. [22] The speciation diagram shows that solutions of citric acid are buffer solutions between about pH 2 and pH 8. In ...
McIlvaine buffer is a buffer solution composed of citric acid and disodium hydrogen phosphate, also known as citrate-phosphate buffer.It was introduced in 1921 by the United States agronomist Theodore Clinton McIlvaine (1875–1959) from West Virginia University, and it can be prepared in pH 2.2 to 8 by mixing two stock solutions.
A simple buffer solution consists of a solution of an acid and a salt of the conjugate base of the acid. For example, the acid may be acetic acid and the salt may be sodium acetate . The Henderson–Hasselbalch equation relates the pH of a solution containing a mixture of the two components to the acid dissociation constant , K a of the acid ...
Outside the transition range the concentration of acid or conjugate base is less than 10 % and the colour of the major species dominates. Species concentrations calculated with the program HySS for a 10 mM solution of citric acid. pK a1 = 3.13, pK a2 = 4.76, pK a3 = 6.40. A weak acid may be defined as an acid with pK a greater than
Therefore, the buffer regions will be centered at about pH 1.3 and pH 4.3. The buffer regions carry the information necessary to get the pK a values as the concentrations of acid and conjugate base change along a buffer region. Between the two buffer regions there is an end-point, or equivalence point, at about pH 3.
This mixture consists of 0.0286 M citric acid, 0.0286 M monopotassium phosphate, 0.0286 M boric acid, 0.0286 M veronal and 0.0286 M hydrochloric acid titrated with 0.2 M sodium hydroxide. The buffer was invented in 1931 by the English chemist Hubert Thomas Stanley "Kevin" Britton (1892–1960) and the New Zealand chemist Robert Anthony Robinson ...
One use of conjugate acids and bases lies in buffering systems, which include a buffer solution. In a buffer, a weak acid and its conjugate base (in the form of a salt), or a weak base and its conjugate acid, are used in order to limit the pH change during a titration process. Buffers have both organic and non-organic chemical applications.