What makes buffer

The balanced equation for this reaction is:. Similarly, if a strong base is added to the mixture, the hydrogen ion concentration decreases by less than the amount expected for the quantity of base added. Buffer solutions are necessary in a wide range of applications. In biology, they are necessary for keeping the correct pH for proteins to work; if the pH moves outside of a narrow range, the proteins stop working and can fall apart. Industrially, buffer solutions are used in fermentation processes and in setting the correct conditions for dyes used in coloring fabrics.

There are a couple of ways to prepare a buffer solution of a specific pH. Then, measure the pH of the solution using a pH probe. The pH can be adjusted up to the desired value using a strong base like NaOH. If the buffer is made with a base and its conjugate acid, the pH can be adjusted using a strong acid like HCl.

Once the pH is correct, dilute the solution to the final desired volume. Probes need to be regularly calibrated with solutions of known pH to be accurate. Alternatively, you can prepare solutions of both the acid form and base form of the solution. Both solutions must contain the same buffer concentration as the concentration of the buffer in the final solution. To get the final buffer, add one solution to the other while monitoring the pH.

In a third method, you can determine the exact amount of acid and conjugate base needed to make a buffer of a certain pH, using the Henderson-Hasselbach equation:. The pH of a buffer solution can be calculated from the equilibrium constant and the initial concentration of the acid. The pH of a buffer can be calculated from the concentrations of the various components of the reaction. The balanced equation for a buffer is:. The strength of a weak acid is usually represented as an equilibrium constant.

The acid-dissociation equilibrium constant K a , which measures the propensity of an acid to dissociate, for the reaction is:. ICE Initial, Change, Equilibrium tables are very helpful tools for understanding equilibrium and for calculating the pH of a buffer solution.

They consist of using the initial concentrations of reactants and products, the change they undergo during the reaction, and their equilibrium concentrations. Consider, for example, the following problem:. Calculate the pH of a buffer solution that initially consists of 0. The equation for the reaction is as follows:. We know that initially there is 0. This change is represented by the letter x in the following table. ICE table — change : Describes the change in concentration that occurs during the reaction.

ICE table — equilibrium : Describes the final concentration of the reactants and products at equilibrium. The Henderson—Hasselbalch equation connects the measurable value of the pH of a solution with the theoretical value pKa. The Henderson—Hasselbalch equation mathematically connects the measurable pH of a solution with the pK a which is equal to -log K a of the acid.

The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in an acid-base reaction. The equation can be derived from the formula of pK a for a weak acid or buffer.

The balanced equation for an acid dissociation is:. In an alternate application, the equation can be used to determine the amount of acid and conjugate base needed to make a buffer of a certain pH.

An example of how to use the Henderson-Hasselbalch equation to solve for the pH of a buffer solution is as follows:. What is the pH of a buffer solution consisting of 0. Worse, available buffers, like phosphate, borate and Tris were ineffective at biological pHs, produced undesired chemical reactions or were toxic to cells.

Norman Good, a professor of plant science at Michigan State University, put an end to this problem. Starting with results published in , Good found about a dozen zwitterionic chemicals neutral molecules containing both a negative and positive charge that worked well in biological experiments. They also had the ability to buffer hydrogen ions between pH 6 and 8 and were not toxic or reactive. There a number of criteria to consider for choosing the right buffer for an experiment.

Here are the main selection factors:. Most biological reactions take place at a pH between 6 and 8, so ideal buffers have pKa values in this range to provide maximum buffering capacity there. Likewise, select a buffer with a pKa slightly higher if you expect your experiment to raise your working pH. Buffers should be very soluble in water, and minimally so in nonpolar solvents fats, oils, and organic solvents. This prevents the buffer from accumulating in cell membranes, vesicles and other nonpolar compartments in biological systems.

A buffer should not readily pass through cell membranes—this also reduces the disproportionate accumulation of buffer in subcellular structures. Highly ionic buffers can cause problems or complications in biological systems. Avoid citrate and phosphate buffers in reactions that are calcium-dependent Tris also chelates calcium. Buffer concentration, temperature, and ionic strength the measure of ion concentration should have minimal impact on the dissociation of the buffer.

If the buffers form complexes with cationic ligands, the complexes should be soluble. Recall that the amount of F - in the solution is 0. Let's double check the pH using the Henderson-Hasselbalch Approximation , but using moles instead of concentrations:. Now let's see what happens when we add a small amount of strong acid, such as HCl. The Cl - is the conjugate base of a strong acid so is inert and doesn't affect pH, and we can just ignore it. In fact, we already discussed what happens. The equation is:.

In this case, the capacity of the buffer will have been exceeded - a situation one tries to avoid. Now, if we add 0. In the process, the 0. Thus, our buffer did what it should - it resisted the change in pH, dropping only from 3. What is a buffer composed of? How does a buffer work? These two reactions can continue to alternate back and forth with little pH change. Selecting proper components for desired pH Buffers function best when the pK a of the conjugate weak acid used is close to the desired working range of the buffer.

Example 1: HF Buffer In this example we will continue to use the hydrofluoric acid buffer. References Brown, et al. Chemistry:The Central Science. Chang, Raymond.