Buffer Solutions: Preparation, Mechanism, Types, and Uses

A buffer solution resists a change in pH when diluted or when small amounts of acid or alkali are added to it.

• They are the aqueous solutions consisting of weak acids and their salts (acid buffers) or weak bases with their salts (basic buffers).
• Buffer solutions are used in several chemical applications.
• Blood is one example of a natural buffer solution.
• The normal pH of human blood is 7.45.
• Alkalosis is a medical condition that causes high blood pH levels (over 7.45).
• Acidosis causes low blood pH levels (below 7.35).
• The other names for buffer solutions are pH buffers and hydrogen ion buffers.

Key Terms: Buffer Solutions, Acids, Bases, and Salts, pH Value, Weak acid, Ammonium acetate, Acetate acid, Sodium acetate, Acidic buffers, Alkaline buffers

---

What are Buffer Solutions?

[Click Here for Sample Questions]

The solutions of a weak acid and its conjugate base, or a weak base and its conjugate acid that can maintain pH are known as buffer solutions.

• This solution resists changes in the concentration of hydrogen ions (pH) when small amounts of acid or base are added.
• Acidity and alkalinity are balanced in both buffers.
• When a tiny amount of a strong acid or a strong base is given to any substance, such as ammonium acetate, it tends to resist any change in its hydrogen ion concentration or pH.
• Buffer solutions consist of a weak acid and salt with a strong base, such as CH3COOH and CH3COONa, or a weak base with a strong acid, such as NH4OH and NH4Cl and salt.

Also check: 

---

Buffer Solution Preparation

[Click Here for Sample Questions]

There are several ways to make a buffer solution with a different pH.

• Firstly, make a solution with acid and its conjugate base by dissolving the acid component of the buffer in approximately 60% of the amount of water required to make the final volume of the solution. 
• Use a pH detector to check the pH of the solution.
• The pH can be adjusted to the appropriate value by using a strong base such as NaOH.
• If the buffer is made from a base and its conjugate acid, the pH can be adjusted with a strong acid such as HCl.
• Once the pH is correct, dilute the solution to the final needed volume. 
• You should also make solutions for both the acid type and the base form of the solution.
• Both solutions must have the same amount of buffer as the final solution.
• To make the final buffer, add one solution to the other while monitoring the pH.

---

Mechanism of Buffering Action

[Click Here for Sample Questions]

To understand how a buffer functions, consider a buffer solution prepared by dissolving sodium acetate in acetic acid.

• Acetic acid, as the name indicates, is an acid: CH₃COOH.
• Sodium acetate dissociates in solution to produce the conjugate base, CH₃COO-acetate ions.

The following is the reaction equation:

\(CH_3COOH \:(aq)+OH^- \: (aq) \:\:\:\longrightarrow \:\:\: CH_3COO^-+H_2O\:(aq)\)

The acetate ion can be neutralized if this solution is combined with a strong acid.

\(CH_3COO^- \:(aq)+H^+ \: (aq) \:\:\:\longrightarrow \:\:\: CH_3COOH\:(aq)\)

It alters the original buffer reaction equilibrium, keeping the pH constant.

---

Types of Buffer Solutions

[Click Here for Sample Questions]

Buffer solutions are widely classified into two types:

• Acidic buffers
• Alkaline buffers

Acid Buffers

These solutions, as the name indicates, are used to keep acidic environments.

• Acid buffer has a pH of acid and is produced by combining a weak acid and its salt with a strong base.
• The pH of an aqueous solution containing equal amounts of acetic acid and sodium acetate is 4.74. 
• These solutions have a pH of less than seven.
• These solutions are comprised of a weak acid and a weak acid salt.
• A mixture of sodium acetate and acetic acid (pH = 4.75) is an example of an acidic buffer solution.

Alkaline Buffers

These buffer solutions are used to maintain basic conditions stable.

• A basic buffer can be produced by mixing a weak base and its salt with a strong acid.
• The pH of an aqueous solution containing equal amounts of ammonium hydroxide and ammonium chloride is 9.25.
• The pH of these solutions is more than seven.
• They contain a weak base and a weak base salt.
• A mixture of ammonium hydroxide and ammonium chloride (pH = 9.25) is an example of an alkaline buffer solution.

---

Henderson-Hasselbalch Equation

[Click Here for Sample Questions]

The Henderson-Hasselbalch equation shows the relationship between acid pH (in aqueous solutions) and acid dissociation constant (pK_a).

When the concentrations of the acid and its conjugate base, or the base and the corresponding conjugate acid, are known, the pH of a buffer solution can be determined using this equation.

Acid Buffer Preparation

Consider a weak acid (HA) and its salt (KA) in an acid buffer solution with a strong base (KOH). The weak acid HA ionizes, and the equilibrium is as follows:

\(HA + H_2O \:\: \leftrightarrows \:\: H^+ + A^-\)

The constant of acid dissociation \(=K_a=[H^+](\frac {[A^-]}{[HA]})\)

Taking negative logs on both sides, we get

\(\Rightarrow-\log K_a=-\log [H^+]-\log (\frac {[A^-]}{[HA]})\)

\(\Rightarrow pK_a=pH-\log (\frac {[salt]}{[acid]})\)

Therefore,

The pH of acid buffer \(=pK_a+(\frac {[salt]}{[acid]})\)

The Henderson-Hasselbalch equation is commonly referred to as the Henderson equation.

Base Buffer Preparation

Consider a basic buffer solution with a strong acid and a weak base (B) and its salt (BA).

pOH can be calculated in the same way as before.

• pOH of a basic buffer \(=pK_b+ \log (\frac {[salt]}{[acid]})\)
• pH of a basic buffer \(=pK_a- \log (\frac {[salt]}{[acid]})\)

Importance of Henderson Equation

The Henderson Equation can be applied to the following situations:

• Used to Calculate the pH of the buffer made from salt and a weak acid/base mixture.
• Used to determine the pKa value.
• Used to make a buffer solution with the required pH.

Henderson-Hasselbalch Equation Limitations

For strong acids and bases, the Henderson-Hasselbalch equation cannot be employed.

Buffering Capacity

The buffer capacity is the number of millimoles of acid or base that must be added to a liter of buffer solution to adjust the pH by one unit.

---

How do Buffers keep the pH Stable?

[Click Here for Sample Questions]

When an acidic or basic component is added to a buffer, the pH does not change. It can neutralize small amounts of acid or base while keeping the pH of the solution steady for a stable reaction.

• Every buffer, whether it's an acid or a basic buffer, has a defined buffer capacity and buffer range.
• The amount of acid or base that can be added before the pH changes is known as buffer capacity.
• Assume we're making a buffer solution by mixing a weak acid with its conjugate base.
• The weak acid does not entirely dissociate in an aqueous solution.
• With the conjugate base anion, just a small quantity of hydrogen cation is dissociated. 
• When we add hydrogen cations (acid) to the solution, they react with conjugate base and reform acid, keeping the pH close to constant.
• If we reverse the process, the pH of the solution will remain practically constant.
• As a result, buffers are required to keep the pH of processes constant.

---

Significance of Buffer Solutions

[Click Here for Sample Questions]

Many chemical reactions are influenced by the acidity of the solution in which they occur. For a specific reaction to occur or occur at a sufficient rate, the pH of the reaction medium must be adjusted. 

• Buffer solutions, which are solutions that maintain a specific pH, allow this control.
• pH has a strong influence on biochemical reactions.
• Most biological compounds contain groups of atoms that can be charged or neutral depending on pH, and the charge or neutrality of these groups has a substantial impact on the biological activity of the molecule.

---

Uses of Buffer Solutions

[Click Here for Sample Questions]

The following are the uses of Buffer solutions

• The use of a bicarbonate and carbonic acid buffer system to manage the pH of animal blood is an example of buffer use in pH regulation.
• Buffer solutions are also used in many organisms to maintain an optimal pH for enzyme activity.
• In the absence of certain buffers, enzyme action may be slowed, enzyme characteristics may be lost, or enzymes may become denatured.
• This denaturation process can potentially permanently disable the catalytic action of the enzymes.

Also check: 

---

Things to Remember

• A buffer solution, or simply a buffer, is a solution that avoids any pH change when a small amount of a strong acid or a strong base is applied to it.
• Acidity and alkalinity are balanced in both buffers.
• When a tiny amount of a strong acid or a strong base is given to any substance, such as ammonium acetate, it tends to resist any change in its hydronium ion concentration or pH.
• Many species employ buffer solutions to maintain an optimal pH for enzyme activity.
• The other names for buffer solutions are pH buffers and hydrogen ion buffers.
• The Henderson-Hasselbalch equation shows the relationship between acid pH (in aqueous solutions) and acid dissociation constant (pK_a).
• The buffer capacity is the number of millimoles of acid or base that must be added to a liter of buffer solution to adjust the pH by one unit.