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Review IM Forces. Section 10.1. Forces Between Particles in Solids and Liquids. Ionic compounds Attractive forces between oppositely charged ions hold ionic compounds together. Ionic bonds are the strongest interparticle force.
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Review IM Forces Section 10.1
Forces Between Particles in Solids and Liquids • Ionic compounds • Attractive forces between oppositely charged ions hold ionic compounds together. • Ionic bonds are the strongest interparticle force. • Smaller the ion and the larger the charge on the ion the stronger the ionic bond
Forces Between Particles in Solids and Liquids • Molecular compounds • Intermolecular (IM) forces between molecules attract molecules to each other in the liquid and solid state. • IM forces are very weak as compared to ionic or covalent bonds
IM Forces Three types of IM Forces • Dipole-dipole force • Hydrogen “bonding” • London dispersion forces See pages 426-428
Interparticle Forces and Physical Properties • The stronger the attractive forces between particles in a liquid or solid, the • Higher the: • Melting point • Boiling point • Surface tension • Viscosity • Lower the: • Vapor pressure
IM Forces • Dipole-dipole forces • Attractive forces between oppositely charged dipoles. • Dipole-dipole forces are found between polar compounds. • The more polar the compound the stronger the dipole-dipole force.
IM Forces • Hydrogen “bonds” • Attractive force between a d+ H bonded to an O, N, or F and a d- O, N, or F on another molecule. • Really a relatively strong dipole-dipole force
Hydrogen Bonding • Hydrogen bonding is the strongest of the IM forces. • H bonding is very important in water and in many biological molecules.
London Dispersion Forces • London Dispersion force • Very weak and short-lasting attractive forces between temporary dipoles • See figure 10.5 • Weakest of the IM forces
London Dispersion Forces • London Dispersion forces • Found between all molecules in liquid/solid state. • Of greatest significance in nonpolar molecules as it’s the only IM force between nonpolar molecules • The larger the molecule the stronger the dipersion forces.
Interparticle Forces • Weakest: London dispersion forces Dipole-dipole force Hydrogen Bonding Strongest: Ionic bond
CH 11: Properties of Solutions • Describing Solutions – concentration units • Energetics of solution formation • Colligative Properties of solutions • BP elevation • FP depression • Osmotic pressure • Vapor Pressure
Terms • Solution – homogeneous mixture • Solvent – generally the larger component of the solution • Determines the physical state of the solution • Solute – generally the smaller component of the solution • Solute is dispersed in the solvent
Solution Composition • Concentrated solution • Dilute solution
Solution Composition • Unsaturated solution • Saturated solution • Supersaturated solution
Concentration Units Molarity (M) = moles solute/Liters solution Mass % = Mass solute/mass solution x100% Mole fraction (cA) = moles A/total moles Molality (m) = moles solute/kg solvent
Solution Formation Formation of a solution involves 3 steps • Separate the solute particles • expand the solute • Separate the solvent particles • Expand the solvent • Form the solution • Solute and solvent interact
Solution Formation • Each step of solution formation involves energy and has a DH. DH1 = energy needed to separate the solute DH2 = energy needed to separate the solvent DH3 = energy released when solution forms
Solution Formation DHsolution = DH1 +DH2 +DH3 Solutions form when the DHsolution is a small value – see page 492
Factors Impacting Solubility • Structure – like dissolves like • #38 on page 520
Factors Impacting Solubility • Pressure • Pressure has little impact on the solubility of liquids and solids • Pressure has a significant impact on the solubility of gases in a liquid • The higher the pressure of gaseous solute above a liquid the higher the concentration of the gas in the solution
Henry’s Law: C = kP • No calculations required. Page 494
Temperature and Solubility • Temperature has variable effects on the amount of solid that will dissolve in an aqueous solution! • See figure 11.6 page 496 • Solutes do dissolve more rapidly at higher temperatures
Temperature and Solubility • The solubility of a gas in water decreases as temperature increases. • See figure 11.7 on page 496 • Thermal pollution – read the story on page 497 when you get a chance
Vapor Pressure of Solutions • See Raoult’s Law on page 498 • Psolution = csolvent P0solvent
Colligative Properties • Colligative properties • properties of a solution that depend upon the amount of dissolved solute, not the identity of the solute. • Freezing point depression • Boiling point elevation • Osmotic Pressure • Note: I will be weaving section 11.7 and the van’t Hoff factor (i) into my consideration of these properties and not consider it separately.
Colligative Properties • FP = Kf m i • BP = Kb m i See page 505 for needed constants
Calculating the bp or fp of a solution • Calculating the molar mass of a solute from fp or bp data
Osmotic Pressure • Osmotic Pressure (P) is often used to determine the molar mass of large biological molecules • See figure 11.17 on page 508 P = MRTi