Buffered solutions equations

Henderson-Hasselbach equation A simplified version of the relationships used in calculations on buffer solutions. 

Calibrating the electrode presents a third complication since a standard with an accurately known activity for H+ needs to be used. Unfortunately, it is not possible to calculate rigorously the activity of a single ion. For this reason pH electrodes are calibrated using a standard buffer whose composition is chosen such that the defined pH is as close as possible to that given by equation 11.18. Table 11.6 gives pH values for several primary standard buffer solutions accepted by the National Institute of Standards and Technology. 

The method of preparation of buffer solutions with the certain acidity value from HMTA and HCl aqueous solutions is offered. It is recommended to use the equations ... 

What is the solubility of CaF2 in a buffer solution containing 0.30 M HCH02 and 0.20 M NaCH02 Hint Consider die equation... 

The pH of the acetic acid-sodium acetate buffer solution is given by the equation ... 

Before leaving the subject of buffer solutions, it is necessary to draw attention to a possible erroneous deduction from equation (21), namely that the hydrogen-ion concentration of a buffer solution is dependent only upon the ratio of the concentrations of acid and salt and upon Ka, and not upon the actual concentrations otherwise expressed, that the pH of such a buffer mixture should not change upon dilution with water. This is approximately although not strictly true. In deducing equation (18), concentrations have been substituted for activities, a step which is not entirely justifiable except in dilute solutions. The exact expression controlling buffer action is ... 

If a buffer solution is diluted, the ionic concentrations are decreased and so, as shown in Section 2.5, the ionic activity coefficients are increased. It follows from equation (26) that the pH is increased. 

This equation is exact, but it can be simplified by applying one of the key features of buffer solutions. Any buffer solution contains both members of a conjugate acid-base pair as major species. In other words, both the weak acid and its conjugate base are present in relatively large amounts. As a result, the change to equilibrium, x, is small relative to each initial concentration, and the equilibrium concentrations are virtually the same as the initial leq linitial " = linitial... 

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. 

We use the seven-step strategy for equilibrium problems, except that we identity this as a buffer solution. This allows us to use the buffer equation in place of an equilibrium constant expression. 

This proton transfer reaction involves the second acidic hydrogen atom of carbonic acid, so the appropriate equilibrium constant is. a 2 > whose p is found in Appendix E p. a 2 — 10.33. Because this is a buffer solution, we apply the buffer equation ... 

Use the seven-step strategy to calculate the pH of the buffer solution using the buffer equation. Then compare the amount of acid in the solution with the amount of added base. Buffer action is destroyed if the amount of added base is sufficient to react with all the acid.The buffering action of this solution is created by the weak acid H2 PO4 and its conjugate base HP04. The equilibrium constant for this... 

The buffer equation indicates that the pH of a buffer solution is close to the p of the acid used to prepare the... 

Because we know we are dealing with a buffer solution made from a specific conjugate acid-base pair, we can work directly with the buffer equation. We need to calculate the ratio of concentrations of conjugate base and acid that will produce a buffer solution of the desired pH. Then we use mole-mass-volume relationships to translate the ratio into actual quantities. 

C18-0049. A buffer solution made from NaHC03 and Nfr2 CO3 has a pH in the range of 9-11. Write balanced equations that show how this buffer system neutralizes H3 and OH"... 

In PAMPA measurements each well is usually a one-point-in-time (single-timepoint) sample. By contrast, in the conventional multitimepoint Caco-2 assay, the acceptor solution is frequently replaced with fresh buffer solution so that the solution in contact with the membrane contains no more than a few percent of the total sample concentration at any time. This condition can be called a physically maintained sink. Under pseudo-steady state (when a practically linear solute concentration gradient is established in the membrane phase see Chapter 2), lipophilic molecules will distribute into the cell monolayer in accordance with the effective membrane-buffer partition coefficient, even when the acceptor solution contains nearly zero sample concentration (due to the physical sink). If the physical sink is maintained indefinitely, then eventually, all of the sample will be depleted from both the donor and membrane compartments, as the flux approaches zero (Chapter 2). In conventional Caco-2 data analysis, a very simple equation [Eq. (7.10) or (7.11)] is used to calculate the permeability coefficient. But when combinatorial (i.e., lipophilic) compounds are screened, this equation is often invalid, since a considerable portion of the molecules partitions into the membrane phase during the multitimepoint measurements. 

The buffer solution works on the basis of Le Chatelier s principle. Consider the equation for the reaction of acetic acid with water ... 

The solution of HC2H302 and C2H302 in H20 results in the relative quantities of each of the species in the equation as shown under the equation. If H30+ is added to the equilibrium system, the equilibrium shifts to use up some of the added H30+. If the acetate ion were not present to take up the added H30+, the pH would drop. Since the acetate ion reacts with much of the added H, 0+, there is little increase in H30+ and little drop in pH. If OH- is added to the solution, it reacts with the H,0+ present. But the removal of that H30+ is a stress, which causes this equilibrium to shift to the right, replacing much of the H30+ removed by the OH-. The pH does not rise nearly as much in the buffered solution as it would have in an unbuffered solution. 

The synthesis of the title compound, 214, the active-site-directed photoaffinity radiolabel for androgen-binding proteins ( ABP ), has been accomplished180,181 by treatment of excess 17a-[( )-2-tributyltin(IV)ethenyl]androsta-4,6-dien-17 -ol-3-one, 215, with sodium iodide-125 of specific activity 27 Cimmol-1 in a sodium acetate-AcOH buffered solution and a solution of 30% H2O2 in glacial AcOH (equation 77). 

We know the initial concentration of NH3 in the buffer solution and can use the pH to find the equilibrium [OH ]. The rest of the solution is organized around the balanced chemical equation. Our first goal is to determine the initial concentration of NH/. 

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. 

Now we can employ equation 19.4 to calculate the molar solubility of Mg(OH)2 in the buffer solution Molar Solubility Mg(OH)2 = [Mg2+]equii... 

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. 

The approximate pH range over which a buffer solution remains effective can be deduced from Figure 3.1. The limits of effective buffering can be seen as the points at which the ratio [AH]/[A ] becomes 10 1 or 1 10 whence substitution in equation (3.20) yields... 

Methods in which the cell potential for the sample solution is compared with that for one or more standards are rapid, simple and readily automated. The measurement of pH is the most common application of this type, one or more buffer solutions serving to calibrate the pH-meter (potentiometer). In all such measurements, calibration involves the evaluation of the constant in the equation... 

Now imagine adding some acid to the solution - either by mistake or deliberately. Clearly, the concentration of H+ will increase. To prevent the value of Ka changing, some of the hydrogen phosphate ions combine with the additional protons to form dihydrogen phosphate (i.e. Equation (6.48) in reverse). The position of the equilibrium adjusts quickly and efficiently to mop up the extra protons in the buffer solution. In summary, the pH is prevented from changing because protons are consumed. 

The Henderson-Hasselbach equation, Equation (6.50), relates the pH of a buffer solution to the amounts of conjugate acid and conjugate base it contains ... 

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