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Buffering agent

For an aqueous solution composed of both a weak acid or base and its conjugate, see Buffer solution. For uses not related to acid-base chemistry, see Buffer.

A buffering agent adjusts the pH of a solution. The function of a buffering agent is to drive an acidic or alkaline solution to a certain pH state and prevent a change in this pH. Buffering agents have variable properties -- some are more soluble than others; some are acidic while others are basic. As pH managers, they are important in many chemical applications, including agriculture, food processing, medicine and photography.

What a buffering agent is

Buffering agents can be either the weak acid or weak base that would comprise a buffer solution. Buffering agents are usually added to water to form buffer solutions. They are the substances that are responsible for the buffering seen in these solutions. These agents are added to substances that are to be placed into acidic or basic conditions in order to stabilize the substance. For example, buffered aspirin has a buffering agent, such as MgO, that will maintain the pH of the aspirin as it passes through the stomach of the patient. Another use of a buffering agent is in antacid tablets, whose primary purpose is to lower the acidity of the stomach.

How a buffering agent works

The way buffering agents work is seen in how buffer solutions work. Using Le Chatelier's principle we get an equilibrium expression between the acid and conjugate base. As a result we see that there is little change in the concentrations of the acid and base so therefore the solution is buffered. A buffering agent sets up this concentration ratio by providing the corresponding conjugate acid or base to stabilize the pH of that which it is added to. The resulting pH of this combination can be found by using the Henderson-Hasselbalch equation:

$\mbox{pH}=\mbox{pKa}+\log_{10}\frac{\left[\mbox{A}^-\right]}{\left[\mbox{HA}\right]}$

where HA is the weak acid and A is the anion of the base.

Buffering Agents Vs. Buffer Solutions

Buffering agents are similar to buffer solutions as a result of the fact that buffering agents are the main components of a buffer solution. They both regulate the pH of a solution and resist changes in pH. A buffer solution maintains the pH for the whole system which is placed into it, whereas a buffering agent is added to an already acidic or basic solution, which it then modifies and maintains a new pH.

Buffering agents and buffer solutions are almost exactly alike except for a few differences:

1. Solutions maintain pH of a system, preventing large changes in it, whereas agents modify the pH of what they are placed into
2. Agents are the active components of a buffer solutions.

Examples

Monopotassium phosphate (MKP) is an example of a buffering agent. It has a mildly acidic reaction; when applied as a fertilizer with urea or diammonium phosphate, it minimizes pH fluctuations which can cause nitrogen loss.

In humans

Buffering agents in humans, functioning in acid base homeostasis, are extracellular agents (e.g., bicarbonate, ammonia) as well as intracellular agents (including proteins and phosphate).

References

• Chemical Principles: The Quest for Insight, Third Edition. Peter Atkins and Loretta Jones
• Quantitative Chemical Analysis, Sixth Edition. Daniel C. Harris