Question:
What is PH buffer or stabilizer?
aqua
2007-01-12 00:07:09 UTC
What is PH buffer or stabilizer?
Seven answers:
ChemGirl
2007-01-12 00:14:20 UTC
A buffer minimizes changes in pH of a system by providing a source of both acid and base. A buffer is typically created by mixing a weak acid and a source of its conjugate base or by mixing a weak base and the source of its conjugate acid. It can also be formed by reacting excess weak acid with a strong base, resulting in the formation of the conjugate. Likewise, excess weak base can be reacted with a strong acid, forming its conjugate.



In any case, when an additional acid is added to the buffer system it reacts with the base present, resulting in minimal pH changes (or when a base is added it reacts with the acid present in the buffer).
adreanna
2007-01-12 08:19:26 UTC
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.



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.



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:



pH=pKa + log10 [A-]/[HA]



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



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 one and the same except for a few differences.



Solutions maintain pH of a system, preventing large changes in it, whereas agents modify the pH of what they are placed into

Agents are the active components of a buffer solutions

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.
Neo
2007-01-12 08:16:32 UTC
Buffer solutions are solutions which resist change in hydronium ion and the hydroxide ion concentration (and consequent pH) upon addition of small amounts of acid or base, or upon dilution. Buffer solutions consist of a weak acid and its conjugate base (more common) or a weak base and its conjugate acid (less common). The resistive action is the result of the equilibrium between the weak acid (HA) and its conjugate base (A−):

HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq)



Any alkali added to the solution is consumed by hydronium ions. These ions are mostly regenerated as the equilibrium moves to the right and some of the acid dissociates into hydronium ions and the conjugate base. If a strong acid is added, the conjugate base is protonated, and the pH is almost entirely restored. This is an example of Le Chatelier's principle and the common ion effect. This contrasts with solutions of strong acids or strong bases, where any additional strong acid or base can greatly change the pH.



When writing about buffer systems they can be represented as salt of conjugate base/acid, or base/salt of conjugate acid. It should be noted that here buffer solutions are presented in terms of the Brønsted-Lowry notion of acids and bases, as opposed to the Lewis acid-base theory (see acid-base reaction theories). Omitted here are buffer solutions prepared with solvents other than water.
sidd the devil
2007-01-12 09:01:38 UTC
PH buffer or stablizer means a solution on adding H+ and OH- ions will not change its Ph value
2007-01-12 08:14:03 UTC
pH buffer is an alkaline Liquid which introduce or make environment for the exact pH value of the solution used for any titration.
♥βετ§¥♥
2007-01-12 08:13:19 UTC
If I remember well....



It is a substance that takes or releases H+ or OH- in order to stabilize the pH of another substance
jolie
2007-01-12 09:40:53 UTC
Buffer solutions are solutions which resist change in hydronium ion and the hydroxide ion concentration (and consequent pH) upon addition of small amounts of acid or base, or upon dilution. Buffer solutions consist of a weak acid and its conjugate base (more common) or a weak base and its conjugate acid (less common). The resistive action is the result of the equilibrium between the weak acid (HA) and its conjugate base (A−):



HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq)

Any alkali added to the solution is consumed by hydronium ions. These ions are mostly regenerated as the equilibrium moves to the right and some of the acid dissociates into hydronium ions and the conjugate base. If a strong acid is added, the conjugate base is protonated, and the pH is almost entirely restored. This is an example of Le Chatelier's principle and the common ion effect. This contrasts with solutions of strong acids or strong bases, where any additional strong acid or base can greatly change the pH.



When writing about buffer systems they can be represented as salt of conjugate base/acid, or base/salt of conjugate acid. It should be noted that here buffer solutions are presented in terms of the Brønsted-Lowry notion of acids and bases, as opposed to the Lewis acid-base theory (see acid-base reaction theories). Omitted here are buffer solutions prepared with solvents other than water





The equilibrium above has the following acid dissociation constant:





Simple manipulation with logarithms gives the Henderson-Hasselbalch equation, which describe pH in terms of pKa:





In this equation



[A−] is the concentration of the conjugate base. This may be considered as coming completely from the salt, since the acid supplies relatively few anions compared to the salt.

[HA] is the concentration of the acid. This may be considered as coming completely from the acid, since the salt supplies relatively few complete acid molecules (A − may extract H + from water to become HA) compared to the added acid.

Maximum buffering capacity is found when pH = pKa, and buffer range is considered to be at a pH = pKa ± 1.





[edit] Illustration of buffering effect: Sodium acetate/acetic acid

The acid dissociation constant for acetic acid-sodium acetate is given by the equation:





Since this equilibrium only involves a weak acid and base, it can be assumed that ionization of the acetic acid and hydrolysis of the acetate ions are negligible. In a buffer consisting of equal amounts of acetic acid and sodium acetate, the equilibrium equation simplifies to



Ka = [H + ],

and the pH of the buffer as is equal to the pKa.



To determine the effect of addition of a strong acid such as HCl, the following mathematics would provide the new pH. Since HCl is a strong acid, it is completely ionized in solution. This increases the concentration of H+ in solution, which then neutralizes the acetate by the following equation.





The consumed hydrogen ions change the effective number of moles of acetic acid and acetate ions:







After accounting for volume change to determine concentrations, the new pH could be calculated from the Henderson-Hasselbalch equation. Any neutralization will result in a small change in pH, since it is on a logarithmic scale.





[edit] Applications

Their resistance to changes in pH makes buffer solutions very useful for chemical manufacturing and essential for many biochemical processes. The ideal buffer for a particular pH has a pKa equal to the pH desired, since a solution of this buffer would contain equal amounts of acid and base and be in the middle of the range of buffering capacity.



Buffer solutions are necessary to keep the right pH for enzymes in many organisms to work. Many enzymes work only under very precise conditions; if the pH strays too far out of the margin, the enzymes slow or stop working and can denature, thus permanently disabling its catalytic activity. A buffer of carbonic acid (H2CO3) and bicarbonate (HCO3−) is present in blood plasma, to maintain a pH between 7.35 and 7.45.



Industrially, buffer solutions are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis and calibration of pH meters.



























Making buffer solutions



[edit] Citric acid-phosphate buffer

Make up 0.1M citric acid and 0.2M phosphate solutions then mix as follows:





Citric acid-phosphate buffers pH 0.2M Na2HPO4 /ml 0.1M Citric Acid /ml

3.0 20.55 79.45

4.0 38.55 61.45

5.0 51.50 48.50

6.0 63.15 36.85

7.0 82.35 17.65

8.0 97.25 2.75


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