PH of buffer

Click Coached Problems for a self-study module on pH of buffer solutions. 

This relation, known as the Henderson-Hasselbalch equation, is often used in biology and biochemistry to calculate the pH of buffers. Historically, it was Henderson who discovered Equation 14.1 in 1908. Hasselbalch put it in logarithmic form eight years later. 

In this section, you compared strong and weak acids and bases using your understanding of chemical equilibrium, and you solved problems involving their concentrations and pH. Then you considered the effect on pH of buffer solutions solutions that contain a mixture of acid ions and base ions. In the next section, you will compare pH changes that occur when solutions of acids and bases with different strengths react together. 

An acid-base titration is a method that allows quantitative analysis of the concentration of an unknown acid or base solution. In an acid-base titration, the base will react with the weak acid and form a solution that contains the weak acid and its conjugate base until the acid is completely neutralized. The following equation is used frequently when trying to find the pH of buffer solutions. 

When you calibrate an electrode with standard buffers, you measure a voltage with the electrode in each buffer. The pH of buffer SI is pHs, and the measured electrode potential in this buffer is Es>- The pH of buffer S2 is pHS2 and the measured electrode potential is s2-The equation of the line through the two standard points is... 

The pH of buffers should always be checked and adjusted prior to use. The use of buffers with lower or higher pH levels will result in under- or overestimations of the pigment content. 

It is very hard to compare results reported in the literature, as there are various variables influencing the data. Concentration of reactants, ratio of amine compound to sugar or carbonyl, reaction in buffer or water, molarity and type of buffer used, pH of buffer, duration of reaction. Rate of carbonyl compounds formation will be the criterion used for reactivity except in few occasions where the percent loss of one of the reactants or both will be referred to in the manuscript. 

The Henderson-Hasselbalch equation shows the same pH as long as the ratio of weak acid to conjugate base is constant. As pointed out before, the pH of buffers is dependent on the total concentration of buffer agents. Equation (2.39) can be transformed to ... 

The eluent used was methanol and buffer (40 60). The concentration of triethylamine acetate in buffer is 2% and the pH of buffer is S.O adjusted by addition of glacial acetic acid. The feed was prepared by dissolving racemic fluoxetine in the mobile phase. Fluoxetine was extracted from Piozace capsule, provided by Lilly Company. 

The Henderson-Hasselbalch equation, which is used to calculate the pH of buffer solutions, is frequently encountered in the biological literature and biochemical texts. It is obtained by expressing each term in Equation 9-29 in the form of its negative logarithm and inverting the concentration ratio to keep all signs positive ... 

Figure 9-4 The effect of dilution of the pH of buffered and unbuffered solutions. The dissociation constant for HA is 1.00 X IQ—. Initial solute concentrations are 1.00 M.

In all but a few situations, the assumption of a single principal equilibrium, as invoked in Examples 15-4 and 15-5, provides a satisfactory estimate of the pH of buffer mixtures derived from polybasic acids. Appreciable errors occur, however, when the concentration of the acid or the salt is very low or when the two dissociation constants are numerically close to one another. A more laborious and rigorous calculation is then required. 

I See the Saunders Interactive General Chemistry CD-ROM, Screen 18.9, pH of Buffer Solutions. 

We have used or expressions or the Henderson-Hasselbalch equation in its acid-salt or base-salt form to find the pH of buffered solutions. Each of these approaches... 

Enantiomers are distinguished on the basis of their interaction with a chiral selector. Development of chiral selectors or chiral stationary phases (CSPs) for GC, HPLC, and CE has rapidly opened a new dimension in the area of chiral drug separation techniques. There are different chiral selectors available for enantiomeric separation of drugs and pharmaceuticals. Finding a suitable chiral selector, whether immobilized on a solid support (GC, HPLC) or added to a running buffer (HPLC, CE), is still often based on trial and error. A few predictions can be made, however, if common structural elements are present. After a selector has been chosen, variables, such as the nature, ionic strength, and pH of buffer, can be varied, as can presence of organic modifiers, temperature, and so on. 

In Chapter Eight, the effect of dilution on the pH of buffer mixtures will be considered in detail. 

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