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Solutions

Solutions. Chapter 12. Types of solutions. Suspensions – largest particle size > 1000nm Blood, paint, aerosols, muddy water Colloids – mid sized particles 2-1000nm Milk, fog, butter Solution – smallest particles <2nm Air, seawater, gasoline. Types of colloids.

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Solutions

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  1. Solutions Chapter 12

  2. Types of solutions • Suspensions – largest particle size • > 1000nm • Blood, paint, aerosols, muddy water • Colloids – mid sized particles • 2-1000nm • Milk, fog, butter • Solution – smallest particles • <2nm • Air, seawater, gasoline

  3. Types of colloids Aerosol – liquid in gas Solid Aerosol – solid in gas Sol -- solid in liquid like protein particles in milk

  4. Emulsion – liquid in liquid like oil droplets in mayonnaise. Foams – gases in liquids like whipped cream Solid emulsion – liquid in a solid like milk in butter Gel – a solid emulsion which is soft but holds its shape like Jell-O

  5. Key terms • Solution - A general term for a solute dissolved in a solvent. A homogeneous mixture of 2 or more components in which particles intermingle at the molecular level. • Solvent - The component of a solution that is the greater quantity. • Solute - The component of a solution that is the lesser quantity.

  6. Solution Types • Gas in gas • Gas in liquid • Gas in solid • Liquid in liquid • Miscible - refers to 2 or more liquids that are infinitely soluble in one another. • Immiscible - refers to 2 liquids that are not soluble in one another and if mixed separate into 2 layers. • Liquid in solid • Solid in liquid • Solid in solid

  7. Dissolving process • solute particles are surrounded by solvent particles and begin go move through the solution in a “solvent cage”. • Ions surrounded by water molecules are called hydrated ions.

  8. Energetics of Dissolving Process • G = H - TS • H can be either + or -, it depends on • the enthalpy to break the crystal apart • the enthalpy of disrupting solvent structure • the enthalpy change for hydrating solute. • S is generally positive.

  9. Energetics of Dissolving Process Costs energy to disrupt solvent and solute structure. H = + Formation of solvent-solute interactions releases energy. H = −

  10. 1.36 g of MgCl2 are dissolved in 47.46 g of water to give a solution with a final volume of 50.00 mL. Calculate the concentration of the solution in mass %, ppm, mole fraction, molarity, and molality.

  11. Hydrochloric acid is sold as a concentrated aqueous solution. The concentration of commercial HCl is 11.7 M and its density is 1.18 g/mL. Calculate the mass percent of HCl in the solution. Calculate the molality of the solution.

  12. Concentrated sulfuric acid has a density of 1.84 g/mL and is 18 M. What is the mass % H2SO4 in the solution? What is the molality of H2SO4 in the solution?

  13. Solubility - the maximum amount of solute than can dissolve in 100 g of solvent at a given temperature. • Saturated solution - a solution that contains the maximum amount of dissolved solute that will dissolve at a given temperature. • Unsaturated solution - a solution that contains less solute than can be dissolved at a given temperature. • Supersaturated solution - a solution that contains more dissolved solute than will ordinarily dissolve at a given temperature.

  14. Factors Affecting Solubility

  15. Temperature • For gases, solubility decreases as temperature increases. • For liquids and solids solubility generally increases as temperature increases.

  16. Pressure • Pressure has very little effect on the solubility of liquids and solids. • Pressure is very important to the solubility of gases however.

  17. Henry’s Law • The solubility of a gas is directly proportional to its partial pressure above the solution. • Or Solubility = kP • where k = henry’s law constant

  18. The solubility of pure N2 (g) at 25oC and 1.00 atm pressure is 6.8 x 10-4 mol/L. What is the solubility of N2 under atmospheric conditions if the partial pressure of N2 is 0.78 atm?

  19. The solubility of pure N2 (g) at 25oC and 1.00 atm pressure is 6.8 x 10-4 mol/L. What is the solubility of N2 under atmospheric conditions if the partial pressure of N2 is 0.78 atm?

  20. Colligative Properties

  21. Vapor pressure lowering • The vapor pressure of a solution is always lower than the vapor pressure of the corresponding pure solvent. • Raoult’s Law • P solution = (P solvent )(X solvent)

  22. What is the vapor pressure of a solution made of 10.0 g of glucose and 100.0 g water at 37.0oC? (Vapor pressure of water at 37oC is 47.1 torr.)

  23. Why is vapor pressure lowered in solutions? • Gvap = Hvap - TSvap

  24. Solutions with a volatile solute • P total = PA + PB • PA = (XA)(PAo) • PB = (XB)(PBo) • PAo is the vapor pressure of the pure solvent.

  25. Boiling point elevation • A non-volatile solute raises the boiling point of a solvent. • Tb = Kb m where • Tb = boiling point elevation • Kb = a constant • m = molality

  26. Freezing point depression • A non-volatile solute depresses the freezing point of a solvent. • Tf = Kf m where • Tf = freezing point depression • Kf = a constant • m = molality

  27. Calculate the FP and BP of a solution containing 100 g of ethylene glycol (C2H6O2) in 900 g H2O. • For water Kb = 0.52 oC/m • Kf = 1.86 oC/m

  28. Tartaric acid can be produced from crystalline residues found in wine vats. It is used in baking powders and as an additive in foods. Analysis show that it is 32.3%C, 3.97% H, and the remainder O. When 1.161 g tartaric acid is dissolved in 11.23 g water, the solution freezes at –1.26oC. Determine the empirical and molecular formula for tartaric acid.

  29. Osmotic Pressure

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