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I. the Nature of Solutions

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I. the Nature of Solutions Solutions The Nature of Solutions Definitions Solution - homogeneous mixture Solute - substance being dissolved Solvent - present in greater amount Types of Solutions SOLUTE – the part of a Solute Solvent Example solution that is being dissolved (usually the solid solid ? lesser amount) solid liquid ? SOLVENT – the part of a solution that gas solid ? dissolves the solute (usually the greater liquid liquid ? amount) gas liquid ? Solute + Solvent = Solution gas gas ? Is it a Solution? Homogeneous Mixture (Solution) Tyndall no Effect? Solution Is it a Solution? Solution • homogeneous • very small particles • no Tyndall effect • particles don’t settle • Ex: •rubbing alcohol Is it a Solution? Homogeneous Mixture (Solution) Tyndall no Effect? yes Solution Suspension, Colloid, or Emulsion Will mixture separate if allowed to stand? no Colloid (very fine solid in liquid) Is it a Solution? Colloid • homogeneous • very fine particles • Tyndall effect • particles don’t settle • Ex: •milk Is it a Solution? Homogeneous Mixture (Solution) Tyndall Effect? no yes Solution Suspension, Colloid, or Emulsion Will mixture separate if allowed to stand? no yes Colloid Suspension or Emulsion Solid or liquid particles? solid Suspension (course solid in liquid) Is it a Solution? Suspension • homogeneous • large particles • Tyndall effect • particles settle if given enough time • Ex: • Pepto-Bismol • Fresh-squeezed lemonade Is it a Solution? Homogeneous Mixture (Solution) Tyndall no Effect? yes Solution Suspension, Colloid, or Emulsion Will mixture separate if allowed to stand? no yes Colloid Suspension or Emulsion Solid or liquid particles? solid liquid Suspension (course solid in liquid) Emulsion (liquid in liquid) Is it a Solution? Emulsion • homogeneous • mixture of two immiscible liquids • Tyndall effect • particles settle if given enough time • Ex: • Mayonnaise Pure Substances vs. Mixtures? Solutions are mixtures!! Examples: graphite -element (C) pepper -hetero. mixture sugar (sucrose) -compound paint -suspension coffee -solution Separation of Solutions Remember that solutions are physical mixtures that can be separated using physical processes like: •Filtration •Cooling •Evaporation Separation of Solutions The components of dyes such as ink may be separated by paper chromatography. Separation of Solutions Distillation Separation of Solutions Filtration Separation of Solutions Evaporation Magnetic Separation Decantation Dissolving vs. Reacting dry Ni(s) + HCl(aq) NiCl2(aq) + H2(g) NiCl2(s) Dissolution is a physical change—you can get back the original solute by evaporating the solvent. If you can’t, the substance didn’t dissolve, it reacted. Solution formation Nature of the solute and the solvent •Whether a substance will dissolve •How much will dissolve Factors determining rate of solution... •Stirred or shaken (agitation) •Particles are made smaller •Temperature is increased Why? Making solutions In order to dissolve, the solvent molecules must come in contact with the solute. Stirring moves fresh solvent next to the solute. The solvent touches the surface of the solute. Smaller pieces increase the amount of surface area of the solute. Temperature and Solutions Higher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often. • Speeds up dissolving. Usually increases the amount that will dissolve (exception is gases) Solvation Solvation – the process of dissolving solute particles are surrounded by solvent particles solute particles are separated and pulled into solution Polar water molecules interacting with positive and negative ions of a salt. Solvation – 3 types of solutes - + - + - + sugar acetic acid salt Non- Weak Strong Electrolyte Electrolyte Electrolyte solute exists as solute exists as solute exists as molecules ions and ions only only molecules DISSOCIATION IONIZATION Electrolytes in the Body • Carry messages to and from the brain as electrical signals • Maintain cellular function with the correct concentrations electrolytes Solvation Dissociation • separation of an ionic solid into aqueous ions NaCl(s) Na+(aq) + Cl–(aq) Solvation Ionization • breaking apart of some polar molecules into aqueous ions + – HNO3(aq) + H2O(l) H3O (aq) + NO3 (aq) Solvation Molecular Solvation • molecules stay intact C6H12O6(s) C6H12O6(aq) Solvation “Like Dissolves Like” NONPOLAR POLAR NONPOLAR POLAR Solvation Soap/Detergent • polar “head” with long nonpolar “tail” • dissolves nonpolar grease in polar water Solubility UNSATURATED SATURATED SUPERSATURATED SOLUTION SOLUTION SOLUTION more solute no more solute becomes unstable, dissolves dissolves crystals form - - - concentration + + + How Much? Solubility- The maximum amount of substance that will dissolve at a specific temperature (g solute/100 g solvent) Saturated solution- Contains the maximum amount of solute dissolved Unsaturated solution- Can still dissolve more solute Supersaturated- solution that is holding more solute than it theoretically can; seed crystal will make it come out Solubility Solubility • Maximum grams of solute that will dissolve in 100 g of solvent at a given temperature • Varies with temp • Based on a saturated solution Solubility Solubility Curve • Shows the dependence of solubility on temperature Solubility Solids are more soluble at... • high temperatures. Gases are more soluble at... • low temperatures & • high pressures (Henry’s Law). .
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