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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.
Table of Content |
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?
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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.
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Buffer Solution Preparation
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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
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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
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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
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The Henderson-Hasselbalch equation shows the relationship between acid pH (in aqueous solutions) and acid dissociation constant (pKa).
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?
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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
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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
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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.
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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 (pKa).
- 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.
Sample Questions
Ques. What is a buffer solution? (1 Mark)
Ans. A buffer solution is a solution made up of a weak acid and its conjugate base, and it is used to prevent a solution's pH from changing.
Ques. What is the purpose of Buffer Solutions? (2 Marks)
Ans. Buffer solutions are used in a wide range of chemical applications to maintain a nearly constant pH level. Buffering is used to regulate pH in a variety of natural systems. The bicarbonate buffering system, for instance, is employed to keep the blood pH in check.
Ques. What is an example of a buffer solution? (2 Marks)
Ans. A buffer solution (or a buffer) is a mixture of a weak acid and its conjugate base (or a mixture of a weak base and its conjugate acid). A buffer containing acetic acid and sodium acetate (CH3COOH + CH3COONa) is an example of a weak acid and its salt.
Ques. What is a basic buffer? (2 Marks)
Ans. A weak base and its salt are mixed with a strong acid to create a basic buffer, which has a basic pH. They're made up of a weak base and its salt. A mixture of ammonium hydroxide and ammonium chloride (pH = 9.25) is one example of an alkaline buffer solution.
Ques. How does a buffer work? (2 Marks)
Ans. Buffers work by neutralizing any added acid (H+ ions) or base (OH- ions) to keep the pH at a stable level, effectively making them a weaker acid or base.
Ques. What is buffer action? (1 Mark)
Ans. Buffer action is the property of a buffer solution to resist any change in pH value even when a modest amount of acid or base is added to it.
Ques. What is the pH range of a basic solution? (1 Mark)
Ans. The pH range of a basic solution is 8-14.
Ques. What characteristics does a buffer solution have? (3 Marks)
Ans. Buffer's Characteristics:
- It has a certain pH level.
- Its pH value does not alter after a lengthy period of storage.
- Dilution has no effect on the pH of the solution.
- Even when a modest amount of a strong acid or a base is added, the pH value does not change.
Ques. What is the pH range of an acidic solution? (1 Mark)
Ans. The pH range of an acidic solution is 0-6.
Ques. How can you tell if a solution is a buffer? (2 Marks)
Ans. A buffer is a concentrated solution of a weak base and its conjugate acid. They work to keep pH fluctuations from becoming too extreme. As a result, a buffer can be made by mixing roughly equal amounts of a weak base and its conjugate acid, or by mixing half an equivalent of a strong acid with a weak base.
Ques. Is it possible for CH3COONa and HCl to make a buffer? (3 Marks)
Ans. Sodium acetate is transformed into acetic acid when the two are combined. However, depending on the amount of acid used, it may be reversible.
CH3COONa + HCl -------> CH3COOH + NaCl
HCl is a powerful acid. It will totally dissociate into H+ and Cl-. CH3COONa, on the other hand, is a weak acid salt. It will be a solid foundation. In this reaction, CH3COONa acts as a base.
As a result, they'll form a buffer.
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