Henderson-Hasselbalch expression

The equation form of the Henderson-Hasselbalch expression [Equation (1.15)] can be further modified by substituting another expression for the bicarbonate term. When excess strong acid is added to plasma, CO2 is sto-ichiometrically released from dissolved CO2, carbonic... 

Since the Henderson-Hasselbalch expression uses pH terms, its utility in clinical situations is less than optimal. Kassirer and Bleich have derived a modified Henderson-Hasselbalch expression that relates [H+], instead of pH, to Pqo2 and HCO, as follows ... 

CHgCOOHffl ) + HjOO) i= H30+(fl ) + CHsCOO-fa ) the Henderson-Hasselbalch expression is ... 

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 ... 

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. 

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 ... 

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. 

The Henderson-Hasselbalch equation is an equation expressing the relationship between pH, pK l, and the log of the ratio of the concentrations of the base to its conjugate acid or an acid to its conjugate base. It is derived from the K l or Kb expression. See Equations (5.26) to (5.30) in the text. They are each a form of this equation. 

The concentration of hydrogen ions liberated by the dissociation of an acid is related to the dissociation constant for that acid and this relationship can be expressed by the Henderson-Hasselbalch equation ... 

Pairs of conjugated acids and bases are always involved in proton exchange reactions (see p.30). The dissociation state of an acid-base pair depends on the concentration. Usually, it is not this concentration itself that is expressed, but its negative decadic logarithm, the pH value. The connection between the pH value and the dissociation state is described by the Henderson-Hasselbalch equation (below). As a measure of the proton transfer potential of an acid-base pair, its pKa value is used—the negative logarithm of the acid constant Kg (where a stands for acid). 

One should always be careful when using the Henderson-Hasselbalch equation pH = pK + log ([A ]/[HA]). The value of [HA] is not always moles of the weak acid per unit volume, cha, that had been added to the moles of the conjugate base per unit volume, Ca-. There are five species for this acid/base equilibria HA, A, H+, OH , and Na+ (or, whatever cation portion of the salt of the conjugate base is present). These species are all interrelated by five expressions ... 

Transformation of the equilibrium equation gives an expression of the H -concentration in solution (Henderson-Hasselbalch equation) ... 

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 ... 

Hasselbalch equation, which is important for understanding buffer action and acid-base balance in the blood and tissues of vertebrates. This equation is simply a useful way of restating the expression for the dissociation constant of an acid. For the dissociation of a weak acid HA into H+ and A-, the Henderson-Hasselbalch equation can be derived as follows ... 

The central equation for buffers is the Henderson-Hasselbalch equation, which is merely a rearranged form of the equilibrium expression. 

The Henderson-Hasselbalch equation (with activity coefficients) is always true, because it is just a rearrangement of the Ka equilibrium expression. Approximations that are not always true are the statements [HA] Fha and [A ] = FA... 

This expression is called the Henderson-Hasselbalch equation. 

The pH of the gastrointestinal tract varies, being 1-2 in the stomach, 5-6 in the duodenum, 6-7 in the jejunum, 7-8 in the ileum, and 8-9 in the large intestine. This variation in pH influences the extent to which acidic or basic chemical substances are ionized, which influences the extent of their absorption. The degree of ionization of an acidic substance or a basic substance at a given pH can be expressed by the Henderson-Hasselbalch equations (equations (2) and (3), respectively) ... 

It is obvious from the above equilibrium that the ratio of ionic to nonionic form of the drug in the solution is controlled by the proton concentration, which is commonly represented by pH values (negative logarithm of proton concentration). Taking the negative logarithm of expression (12-2), the well-known Henderson-Hasselbalch equation could be obtained ... 

This log form of the expression for Ka is called the Henderson-Hasselbalch equation and is useful for calculating the pH of solutions when the ratio [HA]/[A ] is known. 

The Henderson-Hasselbalch equation is very useful in determining the pH at which an indicator changes color. For example, application of Equation (8.2) to the fCa expression for the general indicator HIn yields... 

Note that this expression is the reciprocal of the ratio for the titration of an acid. Substituting this ratio into the Henderson-Hasselbalch equation gives... 

A "0.2 M acetate buffer contains a lolal of 0.2 mole of "acetate per liter. Some of the total acetate is in the conjugate acid form, HO Ac, and some is in the conjugate base form, OAc . The proportions (hence, the concentrations) of each form may be solved by using either the Ka expression or the Henderson-Hasselbalch equation. 

An expression for instantaneous buffer capacity, jS, can be derived using calculus. Essentially, /S is the reciprocal of the slope of the titration curve at any point. Starting with the Henderson-Hasselbalch equation ... 

Rearranging Equation 2-9 into logarithmic form and. substituting the relationships expressed in Equations 2-3 and 2-4 yields the same Henderson-Hasselbalch equation (Eq. 

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 ... 

If the assumptions leading to Equation 9-28 are not valid, the values for [HA] and [A ] are given by Equations 9-24 and 9-25, respectively. If we take the negative logarithms of these expressions, we derive extended Henderson-Hasselbalch equations. 

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... 

Thus we see that a molarity ratio in the acid-salt Henderson-Hasselbalch equation can be treated as a mole (or millimole) ratio. A similar conclusion can be reached for the base-salt version of the Henderson-Hasselbalch equation or for the or expressions that were used in previous buffer calculations. 

The Henderson-Hasselbalch equation was developed independently by the Ameriean biological chemist L. J. Henderson and the Swedish physiologist K. A. Hasselbaleh, for relating the pH to the bicarbonate buffer system of the blood (see below). In its general form, the Henderson-Hasselbalch equation is a useful expression for buffer caleulations. It can be derived from the equilibrium constant expression for a dissociation reaction of the general weak acid (HA) in Equation (1.3) ... 

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