The Usefulness of Buffers
Buffer solutions are one of the most important types of chemical reagent used in chemical research, biological research and industry. Their usefulness stems mostly from their ability to resist changes in pH. If you paid attention in science class, you may recall that pH is a unit of a solution's acidity. For the purpose of this discussion, acidity can be defined as the concentration of hydrogen ions (H+) in solution. How acidic a solution is affects which reactions take place, and how quickly. The ability to control pH is crucial to successfully completing a large number of chemical reactions, and so buffer solutions have a vast number of applications. But first, it's important to understand how buffer solutions work.
Acids and Conjugate Bases
Buffer solutions are usually a combination of an acid and its conjugate base. As we learned above, acidity can be defined as the concentration of H+ ions in solution. Therefore, acids are compounds that release H+ ions into solution. If acids increase the concentration of H+, it follows that the opposites, bases, reduce H+ concentration.
When an acid loses an H+, it creates a conjugate base. This is best illustrated by taking an example, such as CH3COOH (acetic acid). When CH3COOH acts as an acid, it dissociates into H+ and CH3COO- (acetate). CH3COO- is a base, as it can accept H+ to create acetic acid. It is thus the conjugate base of acetic acid, or the base that is produced when acetic acid releases a H+ ion. This concept seems complicated at first, but be assured it isn't hard to pick out conjugate bases in actual reactions. It's essentially what's left of the acid after a H+ ion is released.
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Le Chatelier's Principle and Buffers
Chemical reactions are reversible. Taking our reaction from above as an example,
CH3COOH -----> CH3COO- and H+
CH3COO- and H+ (the products) can combine to form CH3COOH (starting material), which we would term the "reverse reaction." A reaction can thus proceed to the right or left, forward or reverse. Le Chatelier's Principle is a rule stating that the left and right side of the reaction prefer a certain balance or ratio between themselves. In this case, Le Chatelier's Principle basically states that if you add more product (H+ or acetate), the reaction will shift to the left (toward starting materials) and the starting material (acetic acid) will form in response.
Similarly, if more product is added, more starting material will form. When CH3COOH forms, H+ is removed from the solution as it bonds with CH3COO-, and thus the acidity of the solution won't increase. The same general principle applies if a base is added, more H+ is released and the pH of the solution is unchanged. This is the method by which a buffer solution, or a combination of an acid and its conjugate base, can resist changes in pH.
Applications of Buffer Solutions
Your body uses buffers to maintain a blood pH of 7.35-7.45, and also in a massive number of biochemical reactions involving enzymes. Enzymes are very complex compounds often requiring precise pH levels in order to react properly, a role filled by organic buffers produced by your body. For this same reason, buffers are vital for a biologist or chemist performing experiments in the lab. A certain pH will often be required in order for the process being studied to occur, and buffer solutions are the only way to ensure these conditions.
Buffer solutions are also widely used in industry. Industrial processes requiring buffer solutions include fermentation, controlling dye processes and manufacturing pharmaceuticals.