It is a solution containing either a weak acid and its salt or a weak base and its salt , which resists changes in pH . In other words, a buffer is an aqueous solution of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffer solution
Buffers are used to maintain a stable pH in a solution because they can neutralize small amounts of additional base acid.
For a given buffer solution, there is a working pH range and a defined amount of acid or base that can be neutralized before the pH changes. The amount of acid or base that can be added to a buffer before changing its pH is called its buffer capacity.
The Henderson-Hasselbalch equation can be used to measure the approximate pH of a buffer. To use the equation, the initial concentration or stoichiometric concentration is entered in place of the equilibrium concentration.
The general form of a chemical buffer reaction is:
HA ⇌ H + + A –
Also known as: Buffers are also called hydrogen ion buffers or pH buffers.
Properties of Buffer Solutions
They are aqueous solutions
Both the concept of pH and the pH scale only make sense in aqueous solutions, so all buffers or buffers are prepared in water.
Buffers are based on reversible acid / base cleavage reactions that are in equilibrium. By adding strong acids or bases to the medium, this balance is disturbed, so the system reacts to counteract the disturbance, following the principles of Le Chatelier. This is how buffers manage to buffer large changes in pH.
Its pH is easily calculated with the Henderson-Hasselbalch equation
Regardless of the type of buffer, its pH, both before and after adding small amounts of strong acids or strong bases, can be calculated using the Henderson-Hasselbalch equation:
Where [base] refers to the molar concentration of the base (or the conjugate base salt) and [acid] refers to the molar concentration of the acid (or the conjugate acid salt).
They are capable of partially neutralizing both acids and bases
Buffers are made up of a basic substance and an acidic substance, which can neutralize bases and acids, respectively. For this reason, they can buffer the pH after the addition of both strong acids and strong bases.
Its operation depends on the temperature
The pH of a buffer solution depends on the acidity or basicity constant of the weak acid or base it contains. This constant depends on the temperature, so the operation of these solutions also depends on the temperature.
The buffering capacity depends on the total concentration of the solution being greater than the final concentration of the added strong acid or base. For this reason, the higher the total concentration of the buffer, the greater its ability to buffer strong acids or bases.
Components of a buffer solution
Chemically, buffers are made up of only two components. These components can be a weak acid mixed with a salt of its conjugate base or a weak base mixed with a salt of its conjugated acid.
There are two different ways to obtain these components in the same solution, as we will see below:
1. Preparation of buffers by mixing solutions of their components
This is the most direct way to prepare a buffer solution. For this, separate solutions of the weak acid (eg acetic acid) and a salt of the conjugated base (eg sodium acetate) are prepared. Then both solutions are mixed little by little until the desired pH is obtained.
2. Preparation of buffers by partial neutralization of a weak acid solution
In this case, a weak acid solution is prepared with the desired total concentration, and then sodium or potassium hydroxide is added little by little until the desired pH is reached.
Types of buffer solutions Buffer solution
Buffers can be classified according to the types of components they have or according to their final pH.
According to the types of components:
- Weak acid and conjugate base buffer: In these cases the pH depends on the pK a of the weak acid.
- Weak base buffer and conjugated acid: In these cases, the pH depends on the pK b of the weak base.
- Polyprotic acid salts buffer: In some cases, both the one that plays the role of the weak acid and its conjugate base are both salts from the partial neutralization of an acid that has several protons, such as sulfuric or phosphoric acid.
According to its final pH Buffer solution
Depending on the acidity or basicity constant, a buffer solution can regulate the pH around different pH ranges, giving rise to three types of buffers:
- Acid buffers: These are those that regulate the pH around values less than 7. They are prepared with weak acids whose pK a is less than 7 or with weak bases whose pK b is greater than 7.
- Neutral buffers: These are those that regulate the pH around 7. They are usually made up of weak acids or bases that have a pK a or a pK b close to 7.
- Alkaline buffers: These are those that regulate the pH around values greater than 7. They are prepared with weak acids whose pK a is greater than 7 or with weak bases whose pK b is less than 7.
Examples of buffers Buffer solution
Acetic acid / sodium acetate buffer
This is a buffer of a weak acid (acetic acid) and a salt of its conjugate base (sodium acetate). The equilibrium involved and its equilibrium constant are:
This buffer regulates the pH around 4.74 .
Ammonia / Ammonium Chloride Buffer
This is a buffer of a weak base (ammonia or ammonium hydroxide) and a salt of its conjugated acid (ammonium chloride). The equilibrium involved and its equilibrium constant are:
This is an alkaline buffer that regulates the pH around 9.26.
Bisulfate / sulfate buffer
In this case, the bisulfate ion plays the role of a weak acid whose conjugate base is the sulfate ion. The balance involved is:
This is an acidic buffer that regulates the pH around 3.05 .
Carbonic acid / bicarbonate buffer
This buffer regulates the pH around 6.38.
Dihydrogen phosphate / hydrogen phosphate buffer
This is one of the most widely used pH regulation systems in biology and biochemistry, since it allows regulating the pH very close to the physiological pH at which most chemical reactions occur within cells. The reaction is:
This buffer regulates the pH around 7.20.
more examples Buffer solution
- blood – contains a bicarbonate buffer system
- TRIS buffer
- phosphate buffer
Examples of Buffer Solutions in detail
- N H 3 (weak base) and N H 4 Cl (conjugated acid )
- CH 3 COOH(acidgivebil) andCH3COONa (baserun)
- The pH of the sa ngre remains constant between 7.3 and 7.5 margin (slightly basic) through the action of buffers present in the prote INAS the serum SANGUI neo . Said proteins are made up of amino acids that have acidic carboxyl groups (-COOH ) and also basic groups such as amines (-N H 2 ) .
- Mixtures of carbonate ions ( CO 3 2- ) and bicarbonate ions (HCO 3 – )
- Mixtures of acid phosphate ions ( H 2 P O 4 – ) and basic phosphate ions ( HP O 4 2- )
- Formic acid (HC OOH ) and potassium formate (HCOO K ) mixture
- Mixture of benzoic acid ( C 6 H 5 COOH) and potassium benzoate ( C 6 H 5 COONa)
- Mixture of phosphoric acid ( H 3 P O 4 ) and sodium phosphate ( Na 3 P O 4 )
Prepara ion Buffering
To prepare a buffer solution, the following considerations should be taken into account:
- First of all we need to know the pH at which we want to have a buffer solution
- Next we look for an acid or a base that is close to the desired pH
- The pH without buffer is calculated using the Henderson-Hasselbalch equation :
pH =pK a + log ([S] / [A])
- pK a= – log10 K a where K a is the acidity constant
- [ S ] is the concentration of the salt formed by its conjugate base
- [ A ] is the acid concentration
Theory of Acids and Bases:
|Basis||Ionization in aqueous medium||Proton transfer||Electron transfer|
|Acid||H + donating substance||H + donating substance||Substance that donates 2 electrons|
|Base||OH donating substance –||Substance that captures H +||Substance that accepts 2 electrons|
|Equation||HA + BOH → H 2 O + A – + B +||AH + B → A – + BH +||A +: B → A — B –|
|Limitations||Only in aqueous solutions
Acids must have H
Bases must have OH
|Acids must have H||It’s the general theory|
The problems of preparing a buffer solution
Although the simplest buffer solution might consist of just one acid, one base, and water, laboratory technicians often have to prepare several buffers per day, typically consisting of 2–5 components, but could be as many as 20. A typical laboratory might have more than 20 buffer recipes designed to produce 1 liter of buffer.
Calculations with buffer solutions
With a database of over 20 recipes, the first thing a lab technician needs to do is make sure the proper buffer recipe has been selected. For buffer volumes other than 1 liter, recalculate the amounts of all components accordingly and record the new amounts. Any errors in the calculations or in the recording of the new values could lead to incorrect pH values in the buffer solution. With a manual data recording system, the risk of errors is higher.
Weighing and recording of weighing results
When weighing the various components of a buffer solution, care must be taken to use the correct amount of the appropriate component. The actual weight of each component must be recorded and, whether the results are recorded by hand or the values are entered into a computer, care must be taken to avoid transcription errors.
Depending on the required amount of each of the components in the solution and the minimum weight of the balance, it may be necessary to use two different balances, complicating the process and reducing efficiency.
Correct performance of pH meters
Checking the pH level of the buffer solution is vitally important. However, if the pH meter used is not properly calibrated and maintained, the pH readings could be inaccurate. Using a buffer solution with the wrong pH could seriously affect subsequent tests or the quality of the products.
The final buffer solution must be carefully labeled with all information to avoid any confusion. The expiration date is important to ensure that the solution remains effective when used. All data related to the preparation of the buffer solution should be recorded and stored securely for future reference and for traceability purposes.
Buffers pH range
As noted, buffers are useful over specific pH ranges. For example, here is the pH range of common buffering agents:
|citric acid||3.13., 4.76, 6.40||2.1 to 7.4|
|acetic acid||4.8||3.8 to 5.8|
|KH 2 PO 4||7.2||6.2 to 8.2|
|borate||9.24||8:25 a.m. to 10:25 a.m.|
|CHES||9.3||From 8.3 to 10.3|
When a buffer solution is prepared, the pH of the solution is adjusted to bring it into the correct effective range. Typically, a strong acid, such as hydrochloric acid (HCl) is added to lower the pH of the acid buffers. A strong base, such as a solution of sodium hydroxide (NaOH), is added to raise the pH of the alkaline buffers.
How to make sure the pH meter is calibrated correctly
To accurately calibrate your pH meter, you need an accurate calibration of buffers with a known pH. METTLER TOLEDO offers a wide variety of quality pH buffers and ensures the highest precision with NIST / DIN buffers.
Each buffer solution includes a test certificate to help ensure compliance and traceability. Whether you just need a buffer solution or need a technical buffer solution certified by an accredited body, we have the buffer solutions to meet your needs.
How buffers work?
In order to understand how a buffer works, let’s take the example of a buffer solution obtained by dissolving sodium acetate in acetic acid. Acetic acid is (as we can say from the name) an acid: CH 3 COOH, while sodium acetate dissociates in solution to give the conjugate base, the acetate ions of CH 3 COO – . The equation for the reaction is:
CH 3 COOH (aq) + OH – (aq) ⇆ CH 3 COO – (aq) + H 2 O (aq)
If a strong acid is added to this solution, the acetate ion neutralizes it:
CH 3 COO – (aq) + H + (aq) ⇆ CH 3 COOH (aq)
This shifts the balance of the initial buffer reaction, keeping the pH stable. On the other hand, a strong base would react with acetic acid.
Most buffers operate over a relatively narrow pH range. An exception is citric acid because it has three pKa values. When a compound has multiple pKa values, a larger pH range becomes available for a buffer. It is also possible to combine buffers, provided that their pKa values are close (differing by 2 or less), and to adjust the pH with a strong base or an acid to reach the required range. For example, McIvaine’s buffer is prepared by combining mixtures of Na2PO4 and citric acid. Depending on the ratio between the compounds, the buffer can be effective from pH 3.0 to 8.0.
A mixture of citric acid, boric acid, monopotassium phosphate and diethylbarbituic acid can cover the pH range from 2.6 to 12!
Importance of buffer solution in testing
In chemistry laboratories, the Buffer Solution, also known as buffer or buffer, is used to keep the PH constant in mixtures to which strong acids or bases have been added and thus dampen the changes produced by these additions, to ensure the reaction success.
A Buffer Solution is aqueous and is made up of a weak acid and a conjugate base , or failing that, a weak base with a conjugated acid. It is prepared in water, as this is the only way to make sense of the PH scale. It works based on Le Chatelier’s principles of acid-base balance and this is how it manages to dampen the PH changes in a mixture.
The operation of the Buffer Solution will also depend on the temperature it is at when it is added to a sample. Additionally, the more concentrated this solution is, the greater its ability to buffer or regulate the PH of a mixture, the total concentration of the solution, the final concentration of the strong acid or base that is added must be greater.
As we mentioned before, a Buffer Solution is composed only of a base and an acid , which are mixed until the required PH is achieved. To achieve this, there are two most commonly used methods:
1- Preparing separate solutions of weak acid and a conjugated base salt , then mix little by little until the required PH is achieved.
2- Prepare a weak acid solution that has the required total concentration , and then add sodium or potassium hydroxide until the desired PH is achieved.
Regardless of the method used, there is a great variety of Buffer Solutions , all depending on the type of component they have or, failing that, on the final PH required for the test.