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Ian Wilson
Ian Wilson

Buffer Solution

A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an acid or a base aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many living systems that use buffering for pH regulation. For example, the bicarbonate buffering system is used to regulate the pH of blood, and bicarbonate also acts as a buffer in the ocean.

buffer solution


If the pH value of a solution rises or falls too much, the effectiveness of an enzyme decreases in a process, known as denaturation, which is usually irreversible.[5] The majority of biological samples that are used in research are kept in a buffer solution, often phosphate buffered saline (PBS) at pH 7.4.

In industry, buffering agents are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis[4] and calibration of pH meters.

For buffers in acid regions, the pH may be adjusted to a desired value by adding a strong acid such as hydrochloric acid to the particular buffering agent. For alkaline buffers, a strong base such as sodium hydroxide may be added. Alternatively, a buffer mixture can be made from a mixture of an acid and its conjugate base. For example, an acetate buffer can be made from a mixture of acetic acid and sodium acetate. Similarly, an alkaline buffer can be made from a mixture of the base and its conjugate acid.

By combining substances with pKa values differing by only two or less and adjusting the pH, a wide range of buffers can be obtained. Citric acid is a useful component of a buffer mixture because it has three pKa values, separated by less than two. The buffer range can be extended by adding other buffering agents. The following mixtures (McIlvaine's buffer solutions) have a buffer range of pH 3 to 8.[6]

When the difference between successive pKa values is less than about 3, there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. In the case of citric acid, the overlap is extensive and solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.

HEPES is a zwitterionic organic buffer that is also used to maintain physiological pH of cell culture media. HEPES is recommended when the cell culture system is very sensitive, increasing the buffering capacity and stabilizing the pH within the range of 7.2 to 7.6, and is not dependent on CO2 levels.

HEPES is widely used in many biochemical reactions and as a buffering agent in some cell culture media. HEPES has no nutritional benefit to cells. It is added to the media solely for extra buffering capacity when cell culture requires extended periods of manipulation outside of a CO2 incubator.

A common example would be a mixture of ethanoic acid and sodium ethanoate in solution. In this case, if the solution contained equal molar concentrations of both the acid and the salt, it would have a pH of 4.76. It wouldn't matter what the concentrations were, as long as they were the same.You can change the pH of the buffer solution by changing the ratio of acid to salt, or by choosing a different acid and one of its salts.

Note: If you have a very weak acid and one of its salts, this can produce a buffer solution which is actually alkaline! I will comment briefly about this further down the page, but if you are doing buffer solutions at an introductory level this isn't likely to bother you.

A frequently used example is a mixture of ammonia solution and ammonium chloride solution. If these were mixed in equal molar proportions, the solution would have a pH of 9.25. Again, it doesn't matter what concentrations you choose as long as they are the same.

A buffer solution has to contain things which will remove any hydrogen ions or hydroxide ions that you might add to it - otherwise the pH will change. Acidic and alkaline buffer solutions achieve this in different ways.

Because the ammonia formed is a weak base, it can react with the water - and so the reaction is slightly reversible. That means that, again, most (but not all) of the the hydroxide ions are removed from the solution.

HCN is a very weak acid with a Ka of 4.9 x 10-10 mol dm-3. If you had a solution containing an equal numbers of moles of HCN and NaCN, you could calculate (exactly as above) that this buffer solution would have a pH of 9.3.

This isn't something that you need to worry about. Just don't assume that every combination of weak acid and one of its salts will necessarily produce a buffer solution with a pH less than 7.

You could, of course, be asked to reverse this and calculate in what proportions you would have to mix ethanoic acid and sodium ethanoate to get a buffer solution of some desired pH. It is no more difficult than the calculation we have just looked at.

All this means is that to get a solution of pH 4.46, the concentration of the ethanoate ions (from the sodium ethanoate) in the solution has to be 0.5 times that of the concentration of the acid. All that matters is that ratio.

One way of getting this, for example, would be to mix together 10 cm3 of 1.0 mol dm-3 sodium ethanoate solution with 20 cm3 of 1.0 mol dm-3 ethanoic acid. Or 10 cm3 of 1.0 mol dm-3 sodium ethanoate solution with 10 cm3 of 2.0 mol dm-3 ethanoic acid. And there are all sorts of other possibilities.

The modern, and easy, way of doing these calculations is to re-think them from the point of view of the ammonium ion rather than of the ammonia solution. Once you have taken this slightly different view-point, everything becomes much the same as before.

The presence of the ammonia in the mixture forces the equilibrium far to the left. That means that you can assume that the ammonium ion concentration is what you started off with in the ammonium chloride, and that the ammonia concentration is all due to the added ammonia solution.

To summarize, calculating the pH of a buffer based on the equilibrium approach, is very similar to what we do in pH calculations of weak acids and bases. The only difference is that the initial concentration of the conjugate base (or acid if it is a buffer of a weak base and its salt) is not zero in the ICE table.

Comparing the two methods, we have a pH of 4.35 vs 4.37 and this shows that we can make an approximation that x is very small and use the initial concentrations of the buffer components to determine the pH.

The pH 10.00 Buffer Solution is manufactured and ready to use in accordance with and traceable to NIST special publication 260-53 (PB 248-127) to ensure quality and accuracy. Label includes a table to display what the pH value should be given the buffer solution temperature.

Our HEPES buffer solution is suitable for many cell culture systems because it is membrane impermeable, has a limited effect on biochemical reactions, and is chemically and enzymatically stable. The solution is prepared in cell culture grade water.

High-volume manufacturing systems typically have trouble spots that can slow or interrupt workflow. Our Buffer Solutions, individually configured with our Modular Automation System components, are the smart way to create a buffer application that perfectly matches your machines and personnel to your production needs. The result: greater throughput and operational efficiency.

Amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit); in other words, the amount of acid or base a buffer can counteract

BOD dilution water nutrient solutions can be a source of contamination. If you prepare your own solution, make sure you store the phosphate buffer in a refrigerator. Discard any solution if it becomes cloudy or you observe any "chunks" floating in the solution. Using single-use nutrient buffer pillows will avoid many of these pitfalls.

Dilution water should be prepared immediately before use. Without the phosphate buffer, you can prepare dilution water days/weeks ahead of time. Phosphate buffer is a key reagent because phosphorus is the limiting nutrient in stimulating growth, so it must be added the day the water is used.

If you wish to age your dilution water, do not add the single-use nutrient buffers until the day the water is used. Please note that you should not need to age lab reagent water if it is prepared properly.

This demonstration focuses on imparting the concept of a buffer solution to students. Solutions having a pH of 4, 5, 6, 7, 8, 9, 10 are placed in separate labeled Erlenmeyer flasks. Universal indicator is added to each solution. [pH meter is optional]

Distilled water is adjusted to have a pH = 7.0. Half of this solution is placed in beaker "A" . Beaker "A" and its contents are on a stir plate with a magnetic stir bar in the water. Universal indicator solution is added. Next, the demonstrator builds the buffer solution in front of the students starting with deionized water in Beaker "B" and then adding acetic acid. Beaker "B" and its contents are on a stir plate with a magnetic stir bar in the solution. The instructor asks students to estimate the pH of the acetic acid solution and to write the equilibrium equation representing this weak acid system.

The instructor asks students what will happen to the pH of the acetic acid solution when sodium acetate is added. Students should invoke LeChatilier's Principle and the common ion effect. The acetate ion is the common ion. When added to the acetic acid system at equilibrium, the acetate will react with some of the hydronium ions, causing the equilibrium to a shift to the left. Since the hydronium ion concentration decreases, the pH should increase (become less acidic). 041b061a72


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