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| {{About||an aqueous solution composed of both a weak acid or base and its conjugate|Buffer solution|uses not related to acid-base chemistry|Buffer (disambiguation){{!}}Buffer}}
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| A '''buffering agent''' is a weak acid or base used to maintain the acidity ([[pH]]) of a [[solution]] near a chosen value after the addition of another acid or base. That is, the function of a buffering agent is to prevent a rapid change in pH when acids or bases are added to the solution. Buffering agents have variable properties—some are more soluble than others; some are [[acidic]] while others are [[basic (chemistry)|basic]]. As pH managers, they are important in many [[chemical]] applications, including [[agriculture]], [[food processing]], [[biochemistry]], [[medicine]] and [[photography]].
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| ==What is a buffering agent?==
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| A buffering agent can be either a weak acid or weak base. Buffering agents are usually added to water to form a [[buffer solution]], which only slightly changes its pH in response to other acids and bases being combined with it, particularly a [[strong acid]] or a [[strong base]]. Another example is buffered aspirin which has a buffering agent, such as MgO or CaCO<sub>3</sub>, that will help maintain the balance between the acid '''H-A''' (protonated) and the salt '''A<sup>-</sup>''' (deprotonated) forms of aspirin as it passes through the acidic stomach of the patient. The '''H-A''' form of aspirin is a [[covalent]] molecule and is more absorbed by the stomach lining, leading to irritation. The antacid properties of these buffering agents help to maintain the balance toward the salt form by reducing the amount of stomach acid (HCl) which protonates the salt form, '''A<sup>-</sup>'''.
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| ==How a buffering agent works==
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| The way buffering agents work can be seen by calculating how little the pH of buffer solutions will change after addition of a strong acid or a strong base, whereas the same addition would significantly change the pH of a non-buffed solution. Using the [[Henderson-Hasselbalch equation]] we get an equilibrium expression between the acid and conjugate base in terms of the log of the ratio of the acid to conjugate base (the salt of the acid). The concentrations of the weak acid and its salt can change significantly, but the log of their ratio will not. The resulting pH of this combination can be found by using [[Le Chatelier's principle]]. If an added strong base halves the [HA], the [A<sup>-</sup>] will double. Thus the pH will be raised by a factor of log4 or 0.6:
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| :<math>\textrm{pH} = \textrm{pK}_{a}+ \log \left ( \frac{[\textrm{A}^-]}{[\textrm{HA}]} \right )</math>
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| :<math>\textrm{pH}_{new} = \textrm{pK}_{a}+ \log \left ( \frac{[\textrm{A}^-] (2)}{[\textrm{HA}](1/2)} \right )</math> | |
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| :<math>\textrm{pH}_{new} = \textrm{pK}_{a}+ \log \left ( \frac{[\textrm{A}^-]_{original}}{[\textrm{HA}]_{original}} \right )+ \log \left ( 4 \right )</math>
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| For example, if originally the pK<sub>a</sub> = 7 and [HA] = [A<sup>-</sup>], then the pH will be changed from 7.0 to 7.6 after addition of a strong base that halves [HA] and doubles [A<sup>-</sup>]. If a similar addition of 0.001 mol NaOH is made to 1L of non-buffered water, the pH would change from 7 to 11.
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| ==Examples==
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| ===Agriculture===
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| [[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 and simultaneously provides [[potassium]] nutrient.
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| ===In humans===
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| Buffering agents in humans, functioning in [[acid base homeostasis]], are extracellular agents (e.g., [[bicarbonate]], [[ammonia]]) as well as intracellular agents (including [[protein]]s and [[phosphate]]). A dilute mixture of [[monosodium phosphate]] and [[disodium phosphate]] can be made to approach physiological p''H'' and can serve as an agent for phosphate loading or [[enema|colonic lavage]].
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| ===Shampoos and detergents===
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| Most [[shampoos]] are buffered so that they are slightly acidic. The buffer counteracts the alkalinity of [[soap]]. If either of these substances become too acidic or too alkaline, they could damage fabric, and/or skin and hair.
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| ==See also==
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| * [[Buffer solution]]
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| * [[Good's buffers]]
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| ==References==
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| *{{cite book |title=Chemical Principles: The Quest for Insight |edition=Third |authorlink=Peter Atkins |first=Peter |last=Atkins |first2=Loretta |last2=Jones |location=New York |publisher=Freeman |year=2005 |isbn=0-7167-5701-X }}
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| *{{cite book |title=Quantitative Chemical Analysis |edition=Sixth |first=Daniel C. |last=Harris |location=New York |publisher=Freeman |year=2003 |isbn=0-7167-4464-3 }}
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| [[Category:Acid-base chemistry]]
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| [[Category:Buffers]]
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| [[nl:Buffer (scheikunde)]]
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Hello. Let me introduce the writer. Her name is Emilia Shroyer but it's not the most feminine name out there. To collect coins is a factor that I'm completely addicted to. Years in the past he moved to North Dakota and his family enjoys it. Hiring is her working day job now but she's usually wanted her personal business.
Feel free to visit my web blog: berjadigi.com