Henderson-Hasselbalch equation using

The Henderson- Hasselbalch equation, used to calculate the pH of a buffer from the concentrations... 

This relationship is one form of the Henderson-Hasselbalch equation It is a useful relationship m chemistry and biochemistry One rarely needs to cal culate the pH of a solution—pH is more often mea sured than calculated It is much more common that one needs to know the degree of ionization of an acid at a particular pH and the Henderson-Hasselbalch equation gives that ratio... 

Multiprotic weak acids can be used to prepare buffers at as many different pH s as there are acidic protons. For example, a diprotic weak acid can be used to prepare buffers at two pH s and a triprotic weak acid can be used to prepare three different buffers. The Henderson-Hasselbalch equation applies in each case. Thus, buffers of malonic acid (pKai = 2.85 and = 5.70) can be prepared for which... 

Suppose you need to prepare a buffer with a pH of 9.36. Using the Henderson-Hasselbalch equation, you calculate the amounts of acetic acid and sodium acetate needed and prepare the buffer. When you measure the pH, however, you find that it is 9.25. If you have been careful in your calculations and measurements, what can account for the difference between the obtained and expected pHs In this section, we will examine an important limitation to our use of equilibrium constants and learn how this limitation can be corrected. 

Any solution containing comparable amounts of a weak acid, HA, and its conjugate weak base, A-, is a buffer. As we learned in Chapter 6, we can calculate the pH of a buffer using the Henderson-Hasselbalch equation. 

The dissociation constant is most accurately estimated from kinetic data when all of the data points are used in the evaluation. There are several ways to do this. The Henderson-Hasselbalch equation... 

If the pfC, value of a given acid and the pH of the medium are knowrn, the percentages of dissociated and undissociated forms can be calculated using what is called the Henderson-Hasselbalch equation. 

As an example of how to use the Henderson-Hasselbalch equation, let s find out what species are present in a 0.0010 M solution of acetic acid at pH = 7.3. According to Table 20.3, the pKa of acetic acid is 4.76. From the Henderson-Hasselbalch equation, we have... 

Figure 26.1 A titration curve for alanine, plotted using the Henderson-Hasselbalch equation. Each of the two legs is plotted separately. At pH < 1, alanine is entirely protonated at pH = 2.34, alanine is a 50 50 mix of protonated and neutral forms at pH 6.01, alanine is entirely neutral at pH = 9.69, alanine is a 50 50 mix of neutral and deprotonated forms at pH > 11.5, alanine is entirely deprotonated.

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. 

The values of [HA] and [A ] in this expression are the equilibrium concentrations of acid and base in the solution, not the concentrations added initially. However, a weak acid HA typically loses only a tiny fraction of its protons, and so [HA] is negligibly different from the concentration of the acid used to prepare the buffer, [HA]initia. Likewise, only a tiny fraction of the weakly basic anions A- accept protons, and so [A-] is negligibly different from the initial concentration of the base used to prepare the buffer. With the approximations A ] [base]initia and [HA] [acid]initia, we obtain the Henderson-Hasselbalch equation ... 

A note on good practice Keep in mind the approximations required for the use of the Henderson-Hasselbalch equation (that the concentrations of both the weak acid and its conjugate base are much greater than the hydronium ion concentration). Because the equation uses molar concentration instead of activities, it also ignores the interactions between ions. 

In practice, the Henderson-Hasselbalch equation is used to make rapid estimates of the pH of a mixed solution intended to be used as a buffer, and then the pH is adjusted to the precise value required by adding more acid or base and monitoring the solution with a pH meter. 

We can use these numbers to express the range of buffer action in terms of the pH of the solution. The Henderson-Hasselbalch equation shows us that,... 

Step 5 Use an equilibrium table to find the H.O concentration in a weak acid or the OH concentration in a weak base. Alternatively, if the concentrations of conjugate acid and base calculated in step 4 are both large relative to the concentration of hydronium ions, use them in the expression for /<, or the Henderson—Hasselbalch equation to determine the pH. In each case, if the pH is less than 6 or greater than 8, assume that the autoprotolysis of water does not significantly affect the pH. If necessary, convert between Ka and Kh by using Kw = KA X Kb. 

The buffer equation, which is often called the Henderson-Hasselbalch equation, is used to calculate the equilibrium pH of a buffer solution directly from initial concentrations. The approximation is valid as long as the difference between initial concentrations and equilibrium concentrations is negligibly small. As a rule of thumb, the buffer equation can be applied when initial concentrations of H j4 and A differ by less than a factor of 10. Example provides an illustration of the use of the buffer equation. 

Fig. 3.2 Solubility profiles log S-pH. The dashed curves, representing uncharged precipitate in equilibrium with solution of the drugs, were calculated by Henderson-Hasselbalch equations. The dotted horizontal lines are estimates of the solubility of the charged form of the drugs, using either actual data (naproxen) or estimates based on the sdiff 3-4 approximation (atenolol and...

In 1940 Jacobs [25] made use of the Henderson-Hasselbalch equation to relate pH and pKa to membrane transport of ionizable compounds. Extensive experimentation by a group of investigators in the early 1950s [16,26-30] quantitated many of the aforementioned observations concerning the influence of... 

There are two ways of dealing with the bicarbonate buffer system. The first uses the Henderson-Hasselbalch equation and an effective pKa of 6.1. If there is more base (HCO 3) than acid (C02), the pH will always be bigger than the pKa. This is usually the case physiologically (pH = 7.4 pKa = 6.1) so that on a molar basis there is always more than 10-fold more HCO 3 than C02. 

Alternatively, this problem can be solved using the Henderson-Hasselbalch equation ... 

Solving for the ratio of [GNT]/[HCN] that would give a pH of 8.0, we could use the Henderson-Hasselbalch equation ... 

Instead of the algebraic solution, we use the Henderson-Hasselbalch equation, since the final pH falls within one pH unit of the pATa of acetic acid. We let z indicate the increase... 

We use the Henderson-Hasselbalch equation to determine Ki of lactic acid. 

The pATa s of the three acids help us choose the one to be used in the buffer. It is the acid with a pATa within 1.00 pH unit of 3.50. pATa = 3.74 for HCH02, pATa = 4.74 for HC2H302, and p/sTj =2.15 for H3P04. Thus, we choose HCH02 and NaCH02 to prepare a buffer with pH = 3.50. The Henderson-Hasselbalch equation is used to determine the relative amounts of each component present in the buffer solution. 

L (a) We use the Henderson-Hasselbalch equation to determine the pH of the solution. The total solution volume is... 

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