How Buffers Work

A buffer resists changes in pH because the added acid or base is consumed by the buffer. As the buffer is used up, it becomes less resistant to changes in pH. 

In this demonstration,9 a mixture containing approximately a 10 1 mole ratio of HSO, SO - is prepared. Because pKa for HSO, is 7.2, the pH should be approximately 

We can prepare a table showing how the pH should change as the HSO, reacts. 

Through 90% completion, the pH should rise by just 1 unit. In the next 9% of the reaction, the pH will rise by another unit. At the end of the reaction, the change in pH is very abrupt. 

In the formaldehyde clock reaction, formaldehyde is added to a solution containing HSO, SO -, and phenolphthalein indicator. Phenolphthalein is colorless below a pH of 8 and red above this pH. The solution remains colorless for more than a minute. Suddenly the pH shoots up and the liquid turns pink. Monitoring the pH with a glass electrode gave the results in the graph. 

When formaldehyde is added, the net reaction is the consumption of HSOJ, but not of SOl.  

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The usual concerns about acid-base behavior (other than knowing in your soul that it really can t be very important) are where protons go if they re given a choice, how buffers work, and logarithms. Your professor s job is to try to convince you that acid-base behavior has a place in biochemistry. Your job is to learn it—just in case your professor is right. 

In treating buffered solutions in this chapter, we will start by considering the equilibrium calculations. We will then use these results to show how buffering works. That is, we will answer the question How does a buffered solution resist changes in pH when an acid or base is added ... 

Explain how buffers work to control blood pH. (Section 15.7)... 

Explain how buffers work, and write equations to illustrate their action. (Section 9.13)... 

Explain how acid-base balance is maintained in the body. (Section 25.6) Explain how buffers work to control blood pH. (Section 25.7)... 

We will first review the principles of indirect detection, how it works, and what are its requirements. Thereafter, we will focus on considerations concerning buffer composition and sample preparation. The goal is to develop tools that can be used today with commercially available instruments present in many pharmaceutical companies. We will also review available publications and, in an addendum, describe a complete assay for phosphate as a counterion and an impurity. 

To illustrate how a buffer works, consider the simple buffer consisting of acetic acid and the acetate ion HC2H3O2/ C2Hj02 . This buffer is prepared by combining acetic acid and sodium acetate. In solution the two components give the following reactions ... 

Example 8.2 demonstrates the ability of a buffered solution to absorb hydroxide ions without a significant change in pH. But how does a buffer work Suppose a buffered solution contains relatively large quantities of a weak acid HA and its conjugate base A-. Since the weak acid represents the best source of protons, the following reaction occurs when hydroxide ions are added to the solution ... 

How do buffers work A buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. The mixture of ions and molecules in a buffer solution resists changes in pH by reacting with any hydrogen ions or hydroxide ions added to the buffered solution. 

Recognizing Cause and Effect Illustrate how a buffer works using the C2H5NH3+/C2H5NH2 buffer system. Show with equations how the weak base/conjugate acid system is affected when small amounts of acid and base are added to a solution containing this buffer system. 

To understand how buffer solutions work, let s write the equilibrium expression for the ionization of a weak acid HA in the form... 

It should be dear that there are several possible mechanisms by which the protonation state of an enzyme may be altered in low-water media. It will often be desirable to try to maintain the optimal state by controlling acid-base conditions, rather than just relying on pH memory. This can be done by the addition to the reaction system of add-base buffers, as in aqueous media. However, the details of these buffer systems and how they work is usually somewhat different. 

A buffer solution is a solution of an un-ionized weak acid and its conjugate base or an un-ionized weak base and its conjugate acid. We must know three things about buffer solutions (1) their main characteristic, (2) how they are made, and (3) how they work. 

The formation of a buffer solution is an example of the common-ion effect. Explain how a buffer works with reference to a solution containing acetic acid and sodium acetate. 

How do buffers work Buffers work based on the nature of weak acids and their conjugate bases that compose the buffer. If a source of extra hydrogen ion is added to a buffer solution, it reacts with the conjugate base to form the weak acid. If a source of hydroxide ion is added to the buffer, it reacts with the weak acid to form water and the conjugate base. In this way, either added H or OH is used up by adding it to a buffer. This keeps the pH much more stable than if the same acid or base had been added to an unbuffered system. 

The best way to show how a buffer works is in a potential diagram. Similar to matter capacity (see Sect. 6.7), we can introduce the buffer capacity Bp,... 

To understand how a buffer works, let s consider one composed of a weak acid HX and one of its salts MX, where M could be Na, K, or any other cation that does not react with water. The acid-dissociation equilibrium in this buffered solution involves both the acid and its conjugate base ... 

Some of these criteria are self-explanatory, but a discussion of others is needed. A buffer with a high ratio of water solubility to solubility in relatively nonpolar solvents can affect how much organic modifier can be used. A buffer with a low ratio can result in buffer precipitation when an organic solvent is used. Most MEKC experiments are performed at a high pH (>9), but one needs to ensure that the buffer works well in this range. Many buffers are supplied as crystalline acid or bases, and the pH of these buffers is usually not near the pKa when the buffer is placed into solution, so the pH must to be adjusted.The buffer should be selected with a pKa near the desired working pH, and if the pH needs to be adjusted, then the appropriate acid or base should be used. 

To understand how a buffer works, consider a typical buffer system. A solution containing both acetic acid and sodium acetate is a good buffer. The acetic acid in the solution is present as undissociated CH3CO2H. The H , which is in solution, is there because a very small amount of the CH3CO2H has dissociated to H+ and CH3C02 ions. The sodium acetate is present as Na" ion and CH3C02 ion. If some base, such as NaOH, is added, some of the acetic acid reacts ... 

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