Medical Chemistry L5 PDF

Medical Chemistry L5 Lecturer: Prof. Dr. Giovanni N. Roviello Medical Chemistry Teaching for Geomedi University, Tbilisi, Georgia Physical Properties of Solutions and Factors Affecting Solubility Understanding Solution Behavior, Concentration Units, and Factors...

Medical Chemistry L5 Lecturer: Prof. Dr. Giovanni N. Roviello Medical Chemistry Teaching for Geomedi University, Tbilisi, Georgia Physical Properties of Solutions and Factors Affecting Solubility Understanding Solution Behavior, Concentration Units, and Factors Affecting Solubility What is a Solution? A solution is a homogeneous mixture of two or more substances. Typically, solutions consist of a solute (substance dissolved) and a solvent (substance that dissolves the solute). For most solutions, water is the solvent. Physical Properties of Solutions Appearance: Solutions are typically clear and transparent (e.g., sugar in water, salt in water). Homogeneity: Solutions are homogeneous at the molecular level. Particle Size: The solute particles in a solution are less than 1 nanometer in diameter. Effect on Light: Solutions do not scatter light, unlike colloids (Tyndall effect). Boiling and Freezing Points: Solutions generally have altered boiling and freezing points compared to pure solvents (e.g., salt in water lowers freezing point). Vapor Pressure: Solutions generally have a lower vapor pressure than pure solvents. Classification of Solutions Based on State of Solvent: Solid solutions: E.g., alloys like brass (copper + zinc). Liquid solutions: E.g., alcohol in water, sugar in water. Gas solutions: E.g., air (oxygen, nitrogen, other gases). Concentration Levels: Dilute Solutions: Small amount of solute. Concentrated Solutions: Large amount of solute. Saturated Solutions: Maximum solute dissolved at a given temperature. Molecular View of the Solution Process The Solution Process: Breaking of Intermolecular Forces: Involves the breaking of bonds between solute particles (e.g., salt molecules) and between solvent molecules (e.g., water molecules). Formation of New Interactions: New interactions form between the solute and solvent molecules, such as hydrogen bonds in water. Example: Ethanol in Water Ethanol molecules form hydrogen bonds with water molecules. Both the ethanol and water molecules move freely in solution, leading to a uniform mixture. Factors Influencing the Solution Process Nature of the Solute and Solvent: Like dissolves like: Polar solutes tend to dissolve in polar solvents (e.g., salt in water), and non-polar solutes dissolve in non-polar solvents (e.g., oil in hexane). Temperature: Affects solubility of both solids and gases. Pressure: Primarily affects gas solubility.  Quantitative Study of Solutions Concentration: Quantifies the amount of solute in a solution. Types of Concentration Units: Molarity (M): Moles of solute per liter of solution. Formula: Molality (m): Moles of solute per kilogram of solvent. Formula: Percent Composition (by mass): Mass of solute divided by the total mass of solution, multiplied by 100. Formula: Mole Fraction (X): Ratio of moles of a component to the total moles of all components. Formula: Effect of Temperature on Solubility Solubility and Temperature for Solids: Endothermic Dissolution: For most solid solutes, solubility increases with increasing temperature (e.g., sugar in water). Exothermic Dissolution: Some salts, such as calcium sulfate, show decreased solubility with increasing temperature. Gas Solubility and Temperature: General Trend: For gases, solubility decreases as temperature increases (e.g., CO2 dissolving in soda). Explanation: Increasing temperature increases kinetic energy, allowing gas molecules to escape from the solution.  Effect of Pressure on Gas Solubility Henry’s Law: Statement: The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Formula: Where Sg​ is the solubility, kH is the Henry's law constant, and Pg is the partial pressure of the gas. Practical Example: Carbonated Beverages: CO2 dissolves in soda under high pressure. When the pressure is released, CO2 escapes (bubbling). Applications of Henry’s Law: Predicts behavior of gases in solutions, such as oxygen solubility in water and carbon dioxide in soft drinks. Useful in industries like brewing, and carbonated beverages. Le Chatelier’s Principle and Solubility Le Chatelier's Principle: States that if a system at equilibrium is disturbed, the system will shift to counteract the disturbance. Application to Solubility: Endothermic dissolution: Increase in temperature shifts the equilibrium to the right, increasing solubility. Exothermic dissolution: Increase in temperature shifts the equilibrium to the left, decreasing solubility. Summary of Solubility Trends Temperature Effects: Solids: Generally, solubility increases with temperature (endothermic). Gases: Solubility decreases with temperature (exothermic). Pressure Effects: Gases: Solubility increases with increasing pressure (Henry's Law). Solids and Liquids: Pressure has negligible effect on solubility. Concentration Units: Molarity, molality, percent composition, and mole fraction are key methods for expressing solution concentrations. Introduction to Colligative Properties Definition: Colligative properties are physical properties of solutions that depend on the number of solute particles present, not on their identity. Key Concept: These properties only depend on the ratio of solute particles to solvent particles. Colligative Properties Include: Vapor Pressure Depression Boiling Point Elevation Freezing Point Depression Osmotic Pressure Note: These properties are observed when a solute is dissolved in a solvent. Vapor Pressure Depression Vapor Pressure: The pressure exerted by the gas phase of a substance when it is in equilibrium with its liquid phase. Effect of Solute: When a non-volatile solute is added to a solvent, the vapor pressure of the solvent decreases. Why It Happens: Some solvent molecules are replaced by solute molecules at the surface. This reduces the number of solvent molecules able to escape into the gas phase. Raoult’s Law: P= Vapor pressure of the solution Xsolvent = Mole fraction of the solvent P0 = Vapor pressure of the pure solvent Boiling Point Elevation and Freezing Point Depression Boiling Point Elevation: The addition of a solute lowers the vapor pressure, requiring a higher temperature to reach the boiling point. Formula: ΔTb=Kb⋅m Where: ΔTb​ = Change in boiling point Kb​ = Boiling point elevation constant (for a specific solvent) m = Molality of the solution (mol/kg)  Freezing Point Depression:The addition of a solute also lowers the freezing point, as the solution must be at a lower temperature to form solid solvent. Formula: ΔTf=−Kf⋅m Where: ΔTf = Change in freezing point Kf​ = Freezing point depression constant (for a specific solvent) m = Molality of the solution The Van’t Hoff factor (denoted as i) is a coefficient used to account for the number of particles produced by the dissociation of solute in solution.  Osmotic Pressure Definition: Osmotic pressure is the pressure required to stop the osmotic flow of solvent molecules through a semipermeable membrane. Osmosis: The process where solvent moves through a semipermeable membrane from an area of lower solute concentration to higher concentration. Van’t Hoff Equation: π=nRT/V ​ Where: π = Osmotic pressure n = Number of moles of solute R = Ideal gas constant T = Temperature in Kelvin V = Volume of the solution Important Insight: Osmotic pressure is a colligative property as it depends on the concentration of solute particles. The Van’t Hoff factor (denoted as i) is a coefficient used to account for the number of particles produced by the dissociation of solute in solution. Examples of Van't Hoff Factor i: 1. Sodium Chloride (NaCl) in Water: NaCl dissociation: NaCl dissociates completely in water into two ions: Na⁺ and Cl⁻. Van’t Hoff factor: Since NaCl dissociates into 2 ions, the Van't Hoff factor i for NaCl is 2. Example: If 1 mole of NaCl is dissolved in 1 liter of water, the osmotic pressure will be affected by the dissociation of NaCl into 2 particles, so i=2. 2. Ethanol (C₂H₅OH) in Water: Ethanol dissociation: Ethanol does not dissociate into ions in solution; it remains as single molecules. Van’t Hoff factor: Since ethanol does not dissociate, the Van’t Hoff factor i for ethanol is 1. Osmotic Pressure in Biological Systems Application in Cells: Hypertonic Solution: Cells lose water (shrink) when placed in a solution with a higher concentration of solute. Hypotonic Solution: Cells gain water (swell or burst) when placed in a solution with a lower concentration of solute. Real-World Example: Kidney Function: The regulation of osmotic pressure helps in the filtration process within kidneys. Blood Pressure: Osmotic pressure also plays a role in maintaining proper blood volume and pressure. Experimentation: Van’t Hoff's osmotic pressure equation is analogous to the ideal gas law PV=nRT (P=(n/V)RT), and osmotic pressure is a vital tool in fields like biochemistry and medicine. inprotected.com