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CORNELL NOTES

CORNELL NOTES. In the body of the notes: Take notes in class in the format that is most comfortable to you: Outline, text, shorthand, sketches, diagrams, examples Do NOT copy notes word for word think as you write rephrase abbreviate organize. Use the side to list main points

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CORNELL NOTES

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  1. CORNELL NOTES In the body of the notes: Take notes in class in the format that is most comfortable to you: Outline, text, shorthand, sketches, diagrams, examples Do NOT copy notes word for word think as you write rephrase abbreviate organize Use the side to list main points Organize ideas Ask questions such as might be on a test or that you wonder about Use thinking skills to question, bring ideas together, and extend them At the bottom, summarize main ideas at appropriate intervals

  2. SOLUTIONS A solution is a homogeneous mixture; particles are evenly distributed throughout the mixture. Proportions may vary Uniform ratio throughout the mixture A liquid solution is clear. The particles are not visible, do not settle, and can not be filtered. A solution differs from a suspension in that the particles of a suspension are visible, can be filtered, and settle. A solution differs from a colloid in that the particles of a colloid exhibit Tyndall effect., yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight through Jello or dilute milk) A solution will not exhibit the Tyndall effect.

  3. SOLUTIONS Solns homogeneous mixture evenly distributed particles variable proportions uniform ratio Liqsoln clear. particles are not visible, do not settle, and can not be filtered. Notsuspensions: particles of a susp are visible, can be filtered, and settle. Not colloids: particles of a colld show Tyndall effect., yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight dilute milk) A soln will not exhibit the Tyndall effect.

  4. SOLUTIONS Solns homogeneous mixture evenly distributed particles variable proportions uniform ratio liquid soln clear. particles are not visible, do not settle, and can not be filtered. Notsuspensions: particles of a susp are visible, can be filtered, and settle. Not colloids: particles of a colld exhibit Tyndall effect., yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight dilute milk) A solution will not exhibit the Tyndall effect. Define soln Describe soln Are all solns liquid? Contrast liquid solnwith suspand colloids

  5. SOLUTIONS Solns homogeneous mixture evenly distributed particles variable proportions uniform ratio liquid soln clear. particles are not visible, do not settle, and can not be filtered. Notsuspensions: particles of a suspension are visible, can be filtered, and settle. Not colloids: particles of a colloid exhibit Tyndall effect., yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight dilute milk) A solution will not exhibit the Tyndall effect. Define solution Describe solution Are all solns liquid? Contrast liquid solution with suspensions and colloids Solutions are homogenous mixtures with variable proportions and uniform ratios. Separate components are not visible/discernible.

  6. Cherry Kool-aid • Red powder: flavor and color • White crystals: sugar • Clear liquid: water • One substance dissolved in another • Solute: the substance being dissolved • Solvent: the substance that dissolves the solute • Sugar is the SOLUTE (smaller quantity) • Water is the SOLVENT (larger quantity)

  7. Types of Solutions • Gas (solvent is gas) • Gas into Gas: air • Liquid into Gas: humidity • Solid into Gas: air pollution • Liquid (solvent is liquid) • Gas into Liquid: pop • Liquid into Liquid: vinegar • Solid into Liquid: sweet tea • Solid (solvent is solid) • Gas into Solid: absorbent charcoal • Liquid into Solid: dental fillings • Solid into Solid: alloys of metal

  8. The Dissolving Process • Two factors affect the dissolving process: dissolution • The constant motion of the particles (There’s that good old kinetic molecular theory again!) • The polarity of the solute and solvent (Recall that polarity is when a compound has partial charges because of uneven distribution of charges)

  9. Steps of the Dissolving Process • Moving solvent particles cluster around solute molecules or particles at the surface of the solid. • Solvent molecules pull solute off of the solid surface and into solution. • Moving solvent particles continue to spread solute evenly throughout the solution, The process repeats itself as fresh layers of the solute are exposed.

  10. Solvent particles cluster around solute particles at the surface. • Solvent particles pull solute particles away from surface, into solution. • Moving solute particles continue to spread solute evenly through solution. MOLECULAR

  11. Solvent particles cluster around solute particles at the surface. • Solvent particles pull solute particles away from surface, into solution. • Moving solute particles continue to spread solute evenly through solution. IONIC

  12. IONIC COMPOUNDS • When an ionic substance dissolves in water, the forces of the solvent pulling on the ions is stronger than the forces holding the ions together. • The ions separate. This is called DISSOCIATION • Because charged ions are present in an ionic solution, ionic solutions conduct electricity and are called ELECTROLYTES. • EXAMPLE: NaCl

  13. MOLECULAR COMPOUNDS • Certain polar substances form ions when they dissolve in water. This process is called IONIZATION. • Because ions are formed, the solution conducts electricity. • These substance are also ELECTROLYTES. • EXAMPLE: HCl, HC2H3O2

  14. MOLECULAR COMPOUNDS • Other polar substances do not ionize in water. • Because ions are not formed, the solution does not conduct electricity. • These substances that do not ionize in water and do not conduct electricity are called NON-ELECTROLYTES. • EXAMPLE: sugar

  15. ELECTROLYTES: substances that conduct electricity when dissolved in water • Ionic substances that separate into ions (dissociate) or polar molecular substances that form ions (ionization) when dissolved conduct electricity and are called ELECTROLYTES.

  16. FACTORS THAT AFFECT THE RATE OF DISSOLUTION

  17. Think BIG Recall the Pop and Mentos experiment! The pop “explodes” because the dissolved gas rapidly leaves the solution because the candy gives it surfaces to collect on (nucleation sites).

  18. Particles in Solutions • Solvents with non-polar molecules dissolve non-polar substances • Oil, grease, dry cleaning fluid, paint, turpentine • Solvents with polar molecules dissolve polar substances • Water dissolves sugar, ionic compounds • LIKE DISSOLVES LIKE

  19. Terms • Soluble: capable of being dissolved in a particular solvent • Insoluble: incapable of being dissolved in a particular solvent • Miscible: liquids that dissolve freely in any proportion • Immiscible: liquids that are not soluble in each other

  20. Detergents and emulsifiers • Grease is non-polar • Water is polar • DETERGENT has • A non-polar end that dissolves the grease • A polar end that dissolves in the water to rinse it away NONPOLAR DETERGENTPOLAR GREASE WATER

  21. Review • A substance whose water solutions do not conduct electricity is a non-electrolyte. • Many covalent compounds • A substance that separates into ions (dissociates) or forms ions (ionizes) in a water solution conducts electricity and is called an electrolyte • All ionic and some covalent compounds

  22. Solubility • There are limits to the amount of solute that will dissolve in a given amount of solvent at a given temperature • There are some general terms: • Unsaturated • Saturated • Super-saturated

  23. Unsaturated • a solution that can dissolve more of a given solute at a certain temperature • A crystal of solute added to an unsaturated solution will dissolve • When you add a second spoon of sugar to your cup of tea, it dissolves. The tea was an unsaturated solution.

  24. Saturated • a solution that has dissolved all of the solute that it can at a certain temperature • A crystal of solute added to a saturated solution will drop to the bottom, un-dissolved. • When you add three spoons of sugar to your tea, some sugar drops to the bottom, undissolved. It is a saturated solution. • DYNAMIC EQUILIBRIUM exists: • changing but balanced. • Some solid dissolves, but as some dissolves, some re-crystallizes

  25. Super-saturated • an unstable solution that contains more solute than a saturated solution at a certain temperature • A crystal of solute added to a super-saturated solution will cause crystallization. So will any disruption of the unstable solution. • Make a saturated solution at an elevated temperature and cool it slowly. At the lower temperature, the solute will remain dissolved in an unstable situation. If disrupted, the solute crystallizes. • Hot-packs and rock candy

  26. SOLUBILITY CURVE Max g of solute that will dissolve in 100 g of solvent at a given temperature

  27. Concentration: the amount of solute in a given amount of solvent or solution • Dilute: a relatively small amount of solute in a relatively large amount of solvent • Concentrated: a relatively large amount of solute in a relatively small amount of solvent • We can do better!

  28. Percent by volume • mL of solute /100 mL of solution

  29. Percent by mass • g of solute/100 mL of solution

  30. Mass per volume • g solute/1000 mL solution

  31. PPM and PPB • x/1,000,000 • x/1,000,000,000 • Serial dilutions are often used • 1x, 10x, 100x, 1000x, etc.

  32. Molarity • M = mol solute/liter of solution • Chemists use this because it lets us work concentration into stoichiometry problems

  33. Molality • m = mol solute/kg of solvent • Chemists sometimes use this because volume of liquids changes with temperature. Soon, we will be studying the effect of concentration as temperature changes.

  34. Dilutions: a concentrated solution is diluted by adding more solvent to get the desired concentration. • M1V1 = M2V2 • Moles before dilution = Moles after dilution • M = molarity = mol/L • V = volume = L • M x V = mol/L x L = # mol of solute • The # of moles before dilution is equal to the # of moles after dilution. The same # of moles is present in more solvent. The concentration (M, molarity) changes, the volume (V) changes, but not the # of moles of solute (M x V). • Volume units may vary from L, but must be consistent within problem. • So, M1V1 = M2V2

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