Biophysical Explanation of Solutions Part 1 PDF

## **Intermolecular Interactions** There are 3 types of intermolecular interactions: * **Ion-Ion Interaction:** This is the interaction between two oppositely charged ions. The energy of the interaction is determined by the charges of the ions and the distance between them. $U(r)=(qa x qb)/r$ T...

## **Intermolecular Interactions** There are 3 types of intermolecular interactions: * **Ion-Ion Interaction:** This is the interaction between two oppositely charged ions. The energy of the interaction is determined by the charges of the ions and the distance between them. $U(r)=(qa x qb)/r$ This interaction is strong and long-range. It is responsible for the stability of ionic crystals. It also plays a role in solutions containing ions. * **Ion-Dipole Interaction:** This interaction is between an ion and a polar molecule. The energy of this interaction is weaker than the ion-ion interaction. It is responsible for the hydration of ions in solution. $U(r)=(qxyxcos(Ø))/r²$ where: * $q$ is the charge of the ion. * $\mu$ is the dipole moment of the dipole. * $\theta$ is the angle between the electric field of the ion and the dipole moment of the dipole. * $r$ is the distance between the ion and the dipole. * **Dipole-Dipole Interaction:** This interaction is the weakest of the three types of intermolecular interactions. It occurs between two polar molecules. The strength of the interaction depends on the dipole moments of the molecules and the distance between them. **States of Matter** * **Solid**: The distance between molecules is less than RO. * **Liquid**: The distance between molecules is slightly less than RO. * **Gas**: The distance between molecules is greater than RO. **Solutions** A mixture containing only one liquid phase is called a solution. The liquid present in the highest quantity is called the **solvent**, while the other component is the **solute**. There are two types of mixtures : * **Homogeneous mixture**: A mixture where the components are evenly distributed throughout the mixture. The mixture appears as a single phase, and the components cannot be separated by simple physical means like filtration, decantation or sedimentation. * **Heterogeneous mixture**: A mixture where the components are not evenly distributed throughout the mixture. The mixture appears as two or more phases. **Classification of solutions:** A solution can be classified based on: * **Size of molecules:** * **Macromolecule solutions**: Solutions with very large solute molecules. * **Colloids**: Solutions with solute particles of intermediate size, larger than normal molecules but smaller than those in suspension. * **Electrical conductivity:** * **Neutral solution**: A solution that does not conduct electricity. * **Electrolyte solution**: A solution that conducts electricity. This can be either a weak electrolyte, where only a small portion of the solute dissociates into ions in solution; or a strong electrolyte, where the solute completely dissociates into ions upon dissolving. * **Ideal solution**: A solution where the interactions between the solute-solute and solvent-solvent molecules are comparable to the solute-solvent interactions. This condition is often met in dilute solutions. * **Saturation**: * **Saturated solution**: A solution in which the maximum amount of solute is dissolved at a given temperature and pressure. Adding more solute will not dissolve and will settle as a precipitate. * **Unsaturated solution**: A solution in which the amount of the solute is less than the maximum amount that can dissolve at that given temperature and pressure. More solute can be added. * **Concentration:** * **Concentrated solution**: A solution that contains a high concentration of solute in relation to the solvent. * **Diluted solution**: A solution that contains a low concentration of solute in relation to the solvent. * **Dilution formula**: C1V1 = C2V2 * C1 = initial concentration * V1 = initial volume * C2 = final concentration * V2 = final volume **Types of diffusion in liquid phase** * **Migration**: The movement of solutes in a specific direction due to an external force. * **Convection**: The movement of solutes due to the movement of the solvent. * **Diffusion**: The random movement of molecules from regions of high concentration to regions of lower concentration. **Diffusion of a solute in a solvent** The diffusion coefficient is related to temperature and friction by means of the following equations: * D = KT/f * D×M1/3= constant (where D is the diffusion coefficient, K is the Boltzmann constant, T is the temperature, f is the friction coefficient, and M is the molecular weight of the solute) **Diffusion in gels and tissues:** Gels are composed of 95% water, but have a very similar diffusion rate as a solid due to their structural properties. **Membranes** * **Permeable membrane**: Allows all molecules to pass through. * **Selective membrane**: Allows only certain molecules to pass through based on properties like molecular size, charge, and chemical composition. * **Dialysis membrane**: A type of selective membrane that allows small molecules and solvents to pass through while blocking passage of larger molecules like proteins. * **Semipermeable membrane**: Allows only the solvent to pass through. * **Hemipermeable membrane**: Represents a special case of the semipermeable membrane, only allowing certain molecules or solvents to pass through. * **Biological semipermeable membrane**: Allows water, urea, and glucose to pass through. It is used in dialysis. **Colligative properties of solutions:** * **Osmosis**: The movement of a solvent across a semipermeable membrane from a region of high solvent concentration to a region of low concentration. * **Different pressure conditions:** * **When the pressures are equal:** The diffusion is the only factor driving the movement of solvent molecules through the membrane. * **When pressures are unequal:** The pressure gradient causes filtration in addition to diffusion. * **The sum of diffusion and filtration fluxes**: This is defined as the net flux and will determine the direction of the solvent movement. * **Exosmosis**: The solvent moves out of the solution, resulting in higher solute concentration in the solution. * **Endosmosis**: The solvent moves into the solution, diluting the solution and reducing the solute concentration. **Laws of Raoult**: * **First law of Raoult:** This deals with the lowering of vapour pressure. * When a non-volatile (non-evaporating) solute is dissolved in a solvent, the vapour pressure of the solution is less than that of the pure solvent. * **Second law of Raoult:** This deals with the elevation of boiling point. * When a non-volatile solute is dissolved in a solvent, the boiling point of the solution is higher than that of the pure solvent. * **Third law of Raoult:** This deals with the depression of freezing point. * When a non-volatile solute is dissolved in a solvent, the freezing point of the solution is lower than that of the pure solvent. This document covers the essential aspects of intermolecular interactions and the properties of solutions, including colligative properties of solutions. While this text provides a foundation for understanding these concepts, remember that thorough comprehension requires careful study and practice.