Distribution Law introduction | Partition law | Nernst Distribution law | Physical Pharmaceutics -I

Summary

In this video, Khalifa Muhammad Asif from Alia Lana College of Pharmaceutical explains the concept of distribution law in physical science. He discusses the partition of solutes between two immiscible solvents, introducing the statement and mathematical expression of Nernst's distribution law. The video covers applications such as solubility prediction, emulsion stability, and drug development, along with the law's limitations like constant temperature, molecular state consistency, and equilibrium concentration. The video serves as a detailed guide on understanding distribution law and its significance in various scientific fields.

Takeaways

• 📘 The topic covered is the distribution law, also known as partition law, which is important in physical science.
• 🧪 The law involves two immiscible solvents, labeled as solvent A and solvent B, where a solute distributes itself between the two.
• ⚖️ At equilibrium, the rate at which the solute moves between solvent A and solvent B is balanced, leading to dynamic equilibrium.
• 👨‍🔬 The distribution law was formulated by German chemist W.H. Nernst in 1891, based on his study of solute distribution between different solvent pairs.
• 📏 The distribution law states that the ratio of the concentration of solute in two solvents remains constant at a given temperature, represented mathematically as C1/C2 = Kd (distribution coefficient).
• 💡 Applications of the law include determining solubility in different solvents, predicting the stability of oil-water systems, and pharmaceutical drug delivery development.
• 💊 The partition coefficient helps assess drug hydrophobicity and its ability to cross cell membranes, aiding in understanding pharmacokinetic processes.
• 🔍 The law also aids in checking solute association and dissociation in solvents, using the distribution coefficient.
• ⚠️ Limitations of the distribution law include the need for constant temperature, identical molecular conditions in both solvents, and established equilibrium before measurements.
• 🚫 The law is not applicable for high solute concentrations or miscible solvents, requiring dilute solutions and non-miscible solvent pairs.

Q & A

What is the distribution law in physical science?

The distribution law, also known as partition law, states that when a solute is distributed between two immiscible solvents at a constant temperature, the ratio of its concentrations in the two solvents remains constant, as long as the solute remains in the same molecular condition in both solvents.

Who introduced the distribution law and when?

The distribution law was introduced by the German chemist W.H. Nernst in 1891.

What is the mathematical expression of the distribution law?

The distribution law can be mathematically expressed as C1/C2 = Kd, where C1 is the concentration of solute in solvent A, C2 is the concentration of solute in solvent B, and Kd is the distribution coefficient or partition coefficient.

What is the role of the distribution coefficient (Kd) in the distribution law?

The distribution coefficient (Kd) or partition coefficient represents the constant ratio of the concentrations of the solute in two immiscible solvents. It helps in understanding how the solute is distributed between the two solvents.

How can the distribution law be applied in determining solubility?

By knowing the partition coefficient (Kd) and the solubility of the solute in one solvent, we can determine its solubility in another solvent.

What is the significance of the distribution law in pharmaceutical development?

In pharmaceutical development, the distribution law helps in determining the type of delivery system for newly developed drugs, as it provides information about the drug’s hydrophobicity and ability to cross cell membranes, impacting pharmacokinetic processes like absorption, distribution, and elimination.

What is one of the key applications of the partition coefficient in pharmaceuticals?

The partition coefficient is used to measure a drug's hydrophobicity, which is an indication of its ability to cross cell membranes and can help predict pharmacokinetic properties like absorption and distribution.

What are the limitations of the distribution law?

The distribution law has several limitations: it requires constant temperature, the molecular state of the solute must be the same in both solvents, equilibrium concentration must be established before measurements, it doesn't hold for concentrated solutions, and it only applies to immiscible solvents.

Why is temperature important in the application of the distribution law?

Temperature must be kept constant throughout the determination of the partition coefficient because temperature fluctuations can affect the solubility of the solute, leading to deviations in results.

Why is it necessary for the two solvents to be non-miscible for the distribution law to apply?

The distribution law applies only to immiscible solvents because the solute needs to distribute between two separate layers of solvents. If the solvents are miscible, the solute would not be able to establish a distinct partitioning between them.