Buffer Henderson-Hasselbalch equation

Using the buffer (Henderson Hasselbalch) equation, one can calculate the molar ratio of buffer components needed to prepare a buffer of desired pH. This is explained in the following examples. 

As in Example 6.13, the Henderson-Hasselbalch equation provides a simple way to calculate the pH of a buffer and to determine the change in pH upon adding a strong acid or strong base. 

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... 

Although this treatment of buffers was based on acid-base chemistry, the idea of a buffer is general and can be extended to equilibria involving complexation or redox reactions. For example, the Nernst equation for a solution containing Fe + and Fe + is similar in form to the Henderson-Hasselbalch equation. 

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. 

We saw in Section 20.3 that the extent of dissociation of a carboxylic acid HA in an aqueous solution buffered to a given pH can be calculated with the Henderson-Hasselbalch equation. Furthermore, we concluded that at the physiological... 

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 ... 

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,... 

The Henderson-Hasselbalch Equation Describes the Behavior of Weak Acids Buffers... 

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. 3.3 Solubility profiles of sparingly soluble drugs, based on data taken from Avdeef et al. [20]. The solutions consisted of robotically adjusted universal buffers, based on a mixture of Good buffers (see text), and contained 0.2 M KCl. The dashed lines were calculated by the Henderson-Hasselbalch equation and, as can be seen, did not accurately describe the solubility profiles. The solid curves were...

The case of a buffer consisting of a weak base and its acidic form (for example, NH3 and NH4) is treated in an analogous way. Equations of the type of (1.4.26) are sometimes called the Henderson-Hasselbalch equations. 

Fig. 1.9 Dependence of pH on the buffer composition according to the Henderson-Hasselbalch equation (1) acidic buffer (Eq. 1.4.26) (2) basic buffer. Calculation for K A = K B = 10-4, s = 0.1 mol dm-3...

Henderson-Hasselbalch Equation Titration Curves p/—Isoelectric Point The Bicarbonate Buffer Imbalance in Blood pH Acidosis and Alkalosis... 

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. 

For formic acid, pATa = - log(1.8 x 10 4) = 3.74. The Henderson-Hasselbalch equation provides the pH of the original buffer solution ... 

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. 

This is a more basic solution, which we can achieve by increasing the basic component of the buffer solution, the acetate ion. We find out the new acetate ion concentration with the Henderson-Hasselbalch equation. 

Words that can be used as topics in essays 5% rale buffer common ion effect equilibrium expression equivalence point Henderson-Hasselbalch equation heterogeneous equilibria homogeneous equilibria indicator ion product, P Ka Kb Kc Keq KP Ksp Kw law of mass action Le Chatelier s principle limiting reactant method of successive approximation net ionic equation percent dissociation pH P Ka P Kb pOH reaction quotient, Q reciprocal rule rule of multiple equilibria solubility spectator ions strong acid strong base van t Hoff equation weak acid weak base... 

Buffers are solutions that resist a change in pH when we add an acid or base. A buffer contains both a weak acid (HA) and its conjugate base (A-). The acid part will neutralize any base added and the base part of the buffer will neutralize any acid added to the solution. We may calculate the hydronium ion concentration of a buffer by rearranging the Ka expression to yield the Henderson-Hasselbalch equation, which we can use to calculate the pH of a buffer ... 

We can now use these two values for the equilibrium portion of the problem. There are two options for this buffer solution. We can use these concentrations in a Ka calculation, or we can use the Henderson-Hasselbalch equation. Either method will give you the same answer however, the Henderson-Hasselbalch equation is faster. 

The common-ion effect is an application of Le Chatelicr s principle to equilibrium systems of slightly soluble salts. A buffer is a solution that resists a change in pH if we add an acid or base. We can calculate the pH of a buffer using the Henderson-Hasselbalch equation. We use titrations to determine the concentration of an acid or base solution. We can represent solubility equilibria by the solubility product constant expression, Ksp. We can use the concepts associated with weak acids and bases to calculate the pH at any point during a titration. 

Thus, for a weak acid with a given Ka (or pKJ and a given ratio of conjugate base concentration to acid concentration, the pH may be calculated. Or, given the desired pH and IQ (pKa), the ratio of salt concentration to acid concentration can be calculated and the buffer subsequently prepared. Equations (5.26) to (5.30) are each a form of the Henderson-Hasselbalch equation for dealing with buffer solutions. 

What is the Henderson-Hasselbalch equation Tell how it is useful in the preparation of buffer... 

Taking the negative log of both sides yields the Henderson—Hasselbalch equation, which can be used to calculate the pH of a buffer ... 

Since a CA/CB pair is present, this is now a buffer problem, and the Henderson-Hasselbalch equation may be used. 

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