In chemistry, the Henderson-Hasselbalch (often misspelled as Henderson-Hasselbach) equation describes the derivation of pH as a measure of acidity (using pKa, the acid dissociation constant) in biological and chemical systems. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties pH is the measure of the acidity or alkalinity of a Solution. The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions (it is widely used to calculate isoelectric point of the proteins). For an individual weak acid or weak base component see Buffering agent. In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change The isoelectric point (pI is the PH at which a particular Molecule or surface carries no net electrical charge.
Two equivalent forms of the equation are
![\textrm{pH} = \textrm{pK}_{a}+ \log \frac{[\textrm{A}^-]}{[\textrm{HA}]}](../../../../math/a/a/0/aa0d5016a357f0b5679b5924e3bdde67.png)
and
![\textrm{pH} = \textrm{pK}_{a}+\log \left ( \frac{[\mathrm{base}]}{[\mathrm{acid}]} \right ).](../../../../math/0/7/8/0787ab2152d7620e7a9ba8247bc90aac.png)
Here, pKa is − log(Ka) where Ka is the acid dissociation constant, that is:
![\textrm{pK}_{a} = - \log(K_{a}) = - \log \left ( \frac{[\mbox{H}_{3}\mbox{O}^+][\mbox{A}^-]}{[\mbox{HA}]} \right )](../../../../math/9/6/5/9653c53929ea5847c391a5b743e5f8fd.png)
for the non-specific Brønsted acid-base reaction: 
In these equations, A − denotes the ionic form of the relevant acid. Bracketed quantities such as [base] and [acid] denote the molar concentration of the quantity enclosed.
In analogy to the above equations, the following equation is valid:
![\textrm{pOH} = \textrm{pK}_{b}+ \log ( \frac{[\textrm{BH}^+]}{[\textrm{B}]} )](../../../../math/9/0/8/908799347d777ad694b9ba7ec9b142c2.png)
Where B + denotes the salt of the corresponding base B.
Contents |
History
Lawrence Joseph Henderson wrote an equation, in 1908, describing the use of carbonic acid as a buffer solution. Lawrence Joseph Henderson (b June 3 1878 Lynn Massachusetts &ndash d Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3 For an individual weak acid or weak base component see Buffering agent. Karl Albert Hasselbalch later re-expressed that formula in logarithmic terms, resulting in the Henderson-Hasselbalch equation [1]. Karl Albert Hasselbalch ( 1 November 1874, Aastrup Denmark - 19 September 1962) was a physician and chemist In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce Hasselbalch was using the formula to study metabolic acidosis, which results from carbonic acid in the blood. In Medicine, metabolic acidosis is a process which if unchecked leads to acidemia (i Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells €”such as nutrients and oxygen—and transports Waste products
Limitations
There are some significant approximations implicit in the Henderson-Hasselbalch equation. The most significant is the assumption that the concentration of the acid and its conjugate base at equilibrium will remain the same as the formal concentration. This neglects the dissociation of the acid and the hydrolysis of the base. The dissociation of water itself is neglected as well. These approximations will fail when dealing with relatively strong acids or bases (pKa more than a couple units away from 7), dilute or very concentrated solutions (less than 1 mM or greater than 1M), or heavily skewed acid/base ratios (more than 100 to 1).
See also
External links
- Henderson-Hasselbalch Calculator
- Derivation and detailed discussion of Henderson-Hasselbalch equation
- True example of using Henderson-Hasselbalch equation for calculation net charge of proteins
References
- Lawrence J. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Titration is a common laboratory method of Quantitative chemical analysis that is used to determine the unknown Concentration of a known Reactant Acidosis is an increased Acidity (ie an increased Hydrogen ion Concentration) Alkalosis refers to a condition reducing Hydrogen ion concentration of arterial Blood plasma ( alkalemia) Henderson. Concerning the relationship between the strength of acids and their capacity to preserve neutrality. Am. J. Physiol. 1908, 21, 173-179.
- Hasselbalch, K. A. Die Berechnung der Wasserstoffzahl des Blutes aus der freien und gebunden Kohlensäure desselben, und die Sauerstoffbindung des Blutes als Funktion der Wasserstoffzahl Biochemische Zeitschrift 1917, 78, 112-144.
- Po, Henry N. ; Senozan, N. M. Henderson-Hasselbalch Equation: Its History and Limitations. J. Chem. Educ. 2001, 78, 1499-1503.
- de Levie, Robert. The Henderson-Hasselbalch Equation: Its History and Limitations. J. Chem. Educ. 2003, 80, 146.
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