Henderson-Hasselbalch function

Figure 3.2(a) shows a plot of log S versus pH for naproxen, based on re-analysis (unpublished) of the shake-flask [49, 77] and microtiter plate [20] data reported in the literature. The dashed curves in Fig. 3.2 were calculated with the simple Henderson-Hasselbalch equations. For pH pKa, the function reduces to the horizontal line log S = log Sq. For pH pXi, log S is a straight line as a function of pH, exhibiting a slope of 1 (and an intercept of log So-pKj). Where the slope is 0.5, the pH equals to the pKj. 

Dissociation of the neutral acid in water necessitates modifications for air-sea exchange in the model, which is based on Henry s law. Other possible pathways, e.g. sea spray, are neglected. Henry s law is restricted to concentrations of physically solved, non dissociated substances. Since only the non-dissociated acid is volatile, it is important to correct the air-water partition coefficient as to reflect the relative proportions of volatile and non-volatile components. The corrected parameter is the effective Henry s law coefficient, which is related to the Henry s law coefficient as a function of pH (modified Henderson-Hasselbalch equation) ... 

With reference to a solvent, this term is usually restricted to Brpnsted acids. If the solvent is water, the pH value of the solution is a good measure of the proton-donating ability of the solvent, provided that the concentration of the solute is not too high. For concentrated solutions or for mixtures of solvents, the acidity of the solvent is best indicated by use of an acidity function. See Degree of Dissociation Henderson-Hasselbalch Equation Acid-Base Equilibrium Constants Bronsted Theory Lewis Acid Acidity Function Leveling Effect... 

DEGREE OF DISSOCIATION HENDERSON-HASSELBALCH EQUATION ACID-BASE EQUILIBRIUM CONSTANTS BR0NSTED THEORY LEWIS ACID ACIDITY FUNCTION LEVELING EFFECT ACIDITY FUNCTION ACID-LABILE SULFIDES ACID PHOSPHATASE ACONITASE... 

A base exists predominantly as the ionised form at pHpKa. Rearrangement of the Henderson-Hasselbalch equation gives the expressions for the fraction of unionised drug as a function of pH and pKa ... 

Ionization State of Amino Acids Each ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functional group is determined by the relationship between its pifa and the pH of the solution. This relationship is described by the Henderson-Hasselbalch equation. 

Organs and tissues in the body can have very different pHs. The pH of blood is 7.4. The stomach can be as low as 1, while the small intestine is slightly basic at about 8. Functional groups, especially carboxylic acids, can lose or gain a charge as they move from one part of the body to another. If the solution pH and pKa of the acid are known, then the relative concentrations of the acid and its conjugate base can be calculated through the Henderson-Hasselbalch equation (Equation 9.1). 

FIGURE 2.4 Exact and Henderson-Hasselbalch pH as a function of base volume during titration of 100 mL of 0.01 M weak acid. Solid lines without symbols represent the exact pH symbols represent the Henderson-Hasselbalch pH. [Graph reconstructed from data by Po and Senozon, J. Chem. Ed, 78, 1499 (2001).]... 

A buffer solution is a solution that resists changes in pH. If acid is added then, within reason, the pH does not fall if base is added, the pH does not rise. Buffers are usually composed of a mixture of weak acids or weak bases and their salts and function best at a pH equal to the pKa of the acid or base involved in the buffer. The equation that predicts the behaviour of buffers is known as the Henderson-Hasselbalch equation (named after chemists Lawrence Joseph Henderson and Karl Albert Hasselbalch), and is another vitally important equation worth committing to memory. It is derived as follows, by considering a weak acid that ionises in solution ... 

From this expression, commonly known as the Henderson-Hasselbalch equation, It can be seen that the pK of any acid Is equal to the pH at which half the molecules are dissociated and half are neutral (undissociated). This Is because when p/Q, = pH, then log ([A ]/[HA]) = 0, and therefore [A ] = [HA]. The Henderson-Hasselbalch equation allows us to calculate the degree of dissociation of an acid if both the pH of the solution and the p/Q, of the acid are known. Experimentally, by measuring the [A ] and [HA] as a function of the solution s pH, one can calculate the p/Q, of the acid and thus the equilibrium constant TC for the dissociation reaction. 

The Henderson-Hasselbalch equation describes the chemical composition of a buffer as a function of pH. With the Henderson-Hasselbalch equation,... 

The pA a of a compound can be determined by UVA is spectroscopy if either the acidic form or the basic form of the compound absorbs UV or visible light. For example, the phenoxide ion has a A ax at 287 nm. If the absorbance at 287 nm is determined as a function of pH, the of phenol can be ascertained by determining the pH at which exactly one-half the increase in absorbance has occurred (Figure 8.10). At this pH, half of the phenol has been converted into phenoxide. Recall from Section 1.20 that the Henderson-Hasselbalch equation states that the pATa of the compound is the pH at which half the compound exists in its acidic form and half exists in its basic form ([HA] = [A ]). 

This equation is known as the Henderson-Hasselbalch (H-H) equation, and it describes the dependence of the pH as a function of the ratio of molar concentrations of proton acceptor to proton donor of a conjugate acid-base pair in aqueous solution. The size of the logarithmic ratio must be kept as close to 1.0 as possible. The logarithm changes very rapidly when the ratio is much larger or much smaller than 1.0, causing the pH to also change rapidly. In order to maintain the pH to +0.2 units, the ratio must be maintained from about 1.5 to about 0.6. 

Experience shows marked deviation from the Henderson-Hasselbalch equation. There are examples of acid-base titration curves with curves broader than predicted by the Henderson-Hasselbalch equation, an effect called negative cooperativity, and there are examples of acid-base titration curves with curves sharper than predicted by the Henderson-Hasselbalch equation, an effect called positive cooperativity. These deviations from Equation (5.16) can be demonstrated by cooperative interactions involving the charged functional group. 

The degree of dissociation, on the other hand, depends, in a well-defined manner, on the p T of the analyte and the pH of the solution, according to the Henderson-Hasselbalch equation, a, is a function of p Ta and pH for example, for monobasic neutral acids... 

The pH of a solution is a measure of its acidity. The pK value of an ionizable functional group is a measure of the acidity of a proton on that functional group. In your study of general chemistry, you learned that the Henderson-Hasselbalch... 

The dissolution of a drug is a function of the pH of the environment it is exposed to and the pK of the molecule. It is facilitated by the pH gradient in the GI tract as predicted by the Henderson-Hasselbalch equation (equation (7.1)). For instance, basic drugs ionize in the acidic pH of the stomach and the upper parts of the intestine while acidic drugs remain neutral and have very... 

Figure 2.1. Bicarbonate concentration as a function of concentration of carbon dioxide in physical solution. The x-axis shows two equivalent calibration scales, in units either of PCO2 in mmHg or of molecular concentration, in millimoles per litre. Each oblique line joins points at which the hydrogen ion concentration is constant, this being a consequence of the Henderson-Hasselbalch equation.

The variables in the Henderson-Hasselbalch equation are [H ], [HCO3"] and [CO2]. Any pair of these can be used to plot graphs representing acid-base status for each pair, each member can be plotted linearly or logarithmically. This book has explored two methods of representing add-base status. In the earlier chapters, bicarbonate concentration was plotted as a function... 

The pH of this mixture nearly exclusively depends on the concentration ratio of the acid and its conjugate base, assuming that acid as well as base concentrations are higher than hydrogen ion or hydroxyl ion concentrations. Thus, the pH can be set arbitrarily to a predetermined value. This function of buffer solutions can be seen clearly when considering the logarithmic form of Eqs. (2.22) and (2.25), the so-called Henderson-Hasselbalch Eq. (2.26) ... 

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