Buffer Equation, Buffer Capacity and Applications of Buffers

Buffer Equation, Buffer Capacity and Applications of Buffers

Here we understand the what is buffer, buffer capacity & its equitation, applications of buffers

What is Buffer ?

  • A buffer is a solution that resists changes in pH when small amounts of acid or base are added.
  • Buffers are essential in various fields, including chemistry, biology, and medicine.
  • They help maintain a stable pH, which is crucial for the stability and efficiency of many reactions and biological processes.
  • Buffers typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid.
  • When an acid or base is added to a buffer solution, the buffer components react with the added acid or base, preventing a significant change in pH.
  • Buffers are used in chemical reactions, biological systems, analytical chemistry, medicine, and the food and beverage industry, among others.

Application of Buffers

  • Buffers play a crucial role in various industries, including pharmaceuticals, where they are used to maintain the pH levels of drugs and ensure their stability and effectiveness.
  • Here are some specific applications of buffers in the pharmaceutical industry:
  • Stabilization of Drug Components: Buffers are used to prevent the gastrointestinal environment from destroying or altering the pH value of essential drug components, such as aspirin. This helps maintain the drug’s potency and effectiveness.
  • Applications of buffers in Purification of Specific Components: Buffers are used to separate and purify specific components of drugs, such as insulin, ensuring their purity and efficacy.
  • Solubilization of Ingredients: Some drug ingredients are only dissolved at specific pH levels. Buffers are used to ensure that these ingredients are solubilized and available for absorption in the body.
  • Maintenance of Biological Activity: Buffers are essential in biological systems, such as blood, where they help maintain a stable pH despite changes in the environment.
  • Certain drug ingredients, such as pepsin, require specific pH levels to maintain their biological activity. Buffers help ensure that these ingredients remain active and effective.
  • Compatibility with Injection and Eye Drop Formulations: Buffers are used to adjust the pH of drugs to match the pH of the human body, making them suitable for injection or eye drop formulations. This ensures that the drugs are well-tolerated and effective when administered.
  • Inhibition of Gastric Acid Production: Buffers can act as a buffer in the stomach, reducing the production of gastric acid and protecting the stomach lining from damage.
  • Chemical Reactions: Buffers are used in chemical reactions to maintain a constant pH, which is crucial for the stability and efficiency of many reactions.
  • Analytical Chemistry: Buffers are used in analytical chemistry to calibrate instruments and standardize solutions.
  • Medicine: Buffers are used in pharmaceuticals to stabilize the pH of medications and ensure their effectiveness.
  • Applications of buffers in Food and Beverage Industry: Buffers are used in the food and beverage industry to control the pH of products, such as soft drinks and dairy products.
  • In biological systems, buffers play a crucial role in maintaining the pH of the blood at 7.4. The primary buffer in plasma is carbonic acid, which helps regulate the pH of the blood. In erythrocytes, secondary buffers such as oxyhemoglobin and hemoglobin also contribute to pH regulation.
  • Applications of buffers in pharmaceutical systems, buffers are used to adjust the pH of products to ensure maximum stability. For parenteral preparations (i.e., injections), buffers such as acetate, phosphate, citrate, and glutamate are used to maintain a pH of 7.4, which is the pH of the blood. This helps prevent potential harm from large deviations in pH.

Buffer Equation or Henderson-Hasselbalch equation

The buffer equation, also known as the Henderson-Hasselbalch equation, is used to calculate the pH of a buffer solution. It is given by:


Let’s understand ionization of weak acid 

The Henderson-Hasselbalch equation is a fundamental equation in chemistry and biochemistry that relates the pH of a solution to the pKa of its acidic component and the ratio of the concentrations of the conjugate base and the weak acid. The equation is given by:

The derivation of the Henderson-Hasselbalch equation involves the following steps:

Start with the equilibrium expression for the dissociation of the weak acid:

HA ⇌ H+ + A-

The equilibrium constant (Ka) for the dissociation of the weak acid is given by:

Ka = [H+][A-]/[HA]

Take the negative logarithm of both sides of the equation to get:

-log(Ka) = -log([H+][A-]/[HA])

Use the Definition of pH- The negative logarithm of the hydrogen ion concentration ([H+]) is equal to the pH of the solution:

pH = -log([H+])

Rearrange the equation to isolate the pH term:

pH = -log([H+]) = -log([H+]) + log([HA]/[A-]) – log(Ka)

Combine the logarithms using the properties of logarithms:

pH = -log([H+]) + log([HA]/[A-]) – log(Ka)

Use the Definition of pKa- The negative logarithm of the acid dissociation constant (Ka) is equal to the pKa of the weak acid:

pKa = -log(Ka)

Substitute pKa for -log(Ka) in the equation:

pH = -log([H+]) + log([HA]/[A-]) – pKa

Rearrange the equation to get the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

This equation relates the pH of a solution to the pKa of its acidic component and the ratio of the concentrations of the conjugate base and the weak acid. It is a useful tool for understanding and predicting the behavior of weak acid-base systems.

The Henderson-Hasselbalch equation can also be applied to weak bases. 

For a weak base, B, the dissociation reaction is:

B + H2O ⇌ BH+ + OH-

The equilibrium constant (Kb) for the dissociation of the weak base is given by:

Kb = [BH+][OH-]/[B]

Where:

– [BH+] is the concentration of the conjugate acid

– [OH-] is the concentration of hydroxide ions

– [B] is the concentration of the weak base

Taking the negative logarithm of both sides of the equation, we get:

-log(Kb) = -log([BH+][OH-]/[B])

Using the definition of pOH (the negative logarithm of the hydroxide ion concentration), we can rewrite the equation as:

pOH = -log([OH-]) = -log([OH-]) + log([BH+]/[B]) – log(Kb)

Rearranging the equation, we get:

pOH = pKb + log([BH+]/[B])

Since pH + pOH = 14 (at 25°C), we can substitute pOH with 14 – pH:

14 – pH = pKb + log([BH+]/[B])

Rearranging the equation, we get:

pH = 14 – pKb – log([BH+]/[B])

This equation is similar to the Henderson-Hasselbalch equation for weak acids, but with the pKb of the weak base instead of the pKa of the weak acid. It relates the pH of a solution to the pKb of its basic component and the ratio of the concentrations of the conjugate acid and the weak base.

Buffer Capacity

Buffer capacity is a measure of the ability of a buffer solution to resist changes in pH when small amounts of acid or base are added. It is defined as the amount of strong acid or base that must be added to change the pH of a solution by one unit.

Buffer capacity depends on the concentrations of the weak acid and its conjugate base (or the weak base and its conjugate acid), as well as the pH of the solution.

The buffer capacity (β) of a solution is defined as the change in the concentration of either the acid (ΔA) or the base (ΔB) divided by the change in pH (ΔpH) when a small amount of strong acid or base is added to the solution. The formula for buffer capacity is:

β = ΔA or ΔB / ΔpH

Where:

– β is the buffer capacity

– ΔA or ΔB is the change in the concentration of either the acid or the base

– ΔpH is the change in pH

For example, if a buffer solution contains 0.1 M acetic acid (CH3COOH) and 0.1 M sodium acetate (CH3COONa), and the pH of the solution changes from 4.0 to 4.5 when a small amount of strong acid is added, the buffer capacity can be calculated as follows:

ΔA = 0.1 M – 0.05 M = 0.05 M

ΔpH = 4.5 – 4.0 = 0.5

β = ΔA / ΔpH = 0.05 M / 0.5 = 0.1 M/pH

This means that 0.1 mole of strong acid or base must be added to the solution to change the pH by one unit. A higher buffer capacity indicates that the buffer solution can resist changes in pH more effectively.


Read More

  1. Analytical Development
  2. Formulation Development
  3. Quality Assurance
  4. Buffer Equation, Buffer Capacity and Applications of Buffers
  5. Buffer Solution
  6. why ph range is 0 to 14?

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