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Properties of Solutions: Ways of Expressing Concentrations

Properties of Solutions: Ways of Expressing Concentrations. = mass of component in solution. Weight percentage. x 100. total mass of solution. Parts per million (ppm). = mass of component in solution. x 10 6. total mass of solution.

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Properties of Solutions: Ways of Expressing Concentrations

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  1. Properties of Solutions: Ways of Expressing Concentrations = mass of component in solution Weight percentage x 100 total mass of solution Parts per million (ppm) = mass of component in solution x 106 total mass of solution A solution is made containing 6.9 g NaHCO3 per 100 g water. What is the weight percentage of solute in the solution? A 2.5 g sample of ground water was found to contain 5.4 micrograms of Zn2+. What is the concentration of Zn2+ in ppm 6.9g Wt % of component = x 100 = 6.5% 106.9 g 5.4 x 10-6 ppm = x 106 = 2.2ppm 2.5 g

  2. Mole fraction, Molarity , and Molality Mole fraction of a component = Moles component Total moles of all components Calculate the mole fraction of HCl in a solution of HCl containing 36% HCl by weight. 1 mole HCl = 0.99 mol HCl 36 g HCl 36.5 g HCl 1 mole H2O = 3.6 mol H2O 64 g H2O 18 g H2O Mole HCl 0.99 mol = XHCl = = 0.22 4.6 mol Moles HCl + H2O

  3. Mole fraction, Molarity , and Molality Moles of solute Molarity = Liters of solution What is the molarity of an ascorbic acid solution (C6H8O6) prepared by dissolving 1.80 grams in enough water to make 125 mL of solution. How many milliliters of this solution contain 0.0100 mol ascorbic acid. 1 mol C6H8O6 = 0.0102 mol C6H8O6 1.80 g C6H8O6 176 g C6H8O6 0.0102 mol C6H8O6 Molarity = = 0.0818 M .125 L soln

  4. Mole fraction, Molarity , and Molality Molality = moles of solute Kg of solvent What is the molality of a solution made by dissolving 5.0 g of toluene (C7H8) in 25 g of benzene (C6H6)? 1 mol C7H8 = 0.054 mol C7H8 5.0 g C7H8 92 g C7H8 0.054 mol C7H8 Molality = = 2.2 m .025 kg C6H6

  5. Na+ Na+ Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Cl- Properties of Solutions: The Solution Process Solvation or hydration Cl- - - + - + + - +

  6. Properties of Solutions: The Solution Process Energy Changes and Solution Formation Solute-solute interactions Solvent-solvent interactions Solute-solvent interactions  Hsoln =  H1 +  H2+  H3

  7. Properties of Solutions: The Solution Process Energy Changes and Solution Formation NH4OH:  Hsoln = 26.4 NaOH:  Hsoln = -44.48 The overall change in enthalpy can be exo- or endothermic This explains why “like dissolves like”

  8. Properties of Solutions: Solution Formation, Spontaneity and Disorder…WHY DOES THIS STUFF DISSOLVE? London dispersion forces bp = 69 bp = 77 Little energy is exchanged

  9. Properties of Solutions: Solution Formation, Spontaneity and Disorder…WHY DOES THIS STUFF DISSOLVE? Processes in which the energy content of the system decreases tend to occur spontaneously. Processes in which the disorder of the system increases tend to occur spontaneously When molecules of different types are brought together, an increase in disorder occurs spontaneously unless the molecules are restrained sufficiently by strong intermolecular forces. Salt does not dissolve in gasoline because strong forces are holding the Na+ and Cl- ions together and the intermolecular forces associated with nonpolar substances is not sufficient to dislodge them.

  10. Properties of Solutions: Saturated Solutions and Solubilityc As solid solute begins to dissolve in a solvent, the concentrations of solute particles in solution increases, so the chances of their colliding with the surface of the solid increases. This may lead to crystallization. Saturated: a solution with undissolved solute dissolve Solute + Solvent  Solution Supersaturated: a solution which contains a greater amount of solute than needed to form a saturated solution crystallize

  11. Properties of Solutions: Factors Affecting Solubility • As a rule, solubility increases with increasing molecular mass • Polar liquids tend to dissolve in polar solvents. If the dissolve they are miscible. • If they do not dissolve they are immiscible

  12. Properties of Solutions: Factors Affecting Solubility Hydrogen-boning interactions between solute and solvent may lead to high solubility Because of H-bonding, solute-solute, solvent-solvent, and solute-solvent interactions are not appreciably different. Ethanol and water Ethanol and ethanol There is no significant change in the environment

  13. Properties of Solutions: Factors Affecting Solubility However, the numbers carbon atoms in an alcohol does effect it solubility in water. As the length of the chain increases, the OH groups decrease leading to a decrease in solubility

  14. Properties of Solutions: Factors Affecting Solubility Substances with similar intermolecular attractive forces tend to be soluble in one another….LIKE DISSOLVES LIKE Glocuse has 5-OHgroups on a six carbon framework which makes the molecule fairly soluble in water

  15. Properties of Solutions: Factors Affecting Solubility Substances with similar intermolecular attractive forces tend to be soluble in one another….LIKE DISSOLVES LIKE Predict whether each of the following substances is more likely to dissolve in carbon tetrachloride or water: C7H16. NaHCO3, HCl

  16. Pressure Effects The solubility of a gas in any solvent is increased as the pressure of the gas over the solvent increases By contrast the solubility of solids and liquids are not appreciable affected by pressure.

  17. The relationship between pressure and solubility is expressed by Henry’s Law: Cg = kPg where Cg is the solubility of the gas in the solution phase, Pg is the partial pressure of the gas over the solution, and k is a Henry’s law constant which differs from one solute-solvent pair to another. For example the solubility of N2 gas in water at 25 ° C and 0.78 atm. is 5.3 x 10-4 M k = 5.3 x 10-4 M/0.78 = 6.8 x 10-4 mol/l-atm. Assume that the partial pressure of the N2 is doubled, Henry’s law, Cg = kPg predicts that the solubility will also double. Cg = kPg Cg = (6.8 x 10-4 mol/l-atm)(1.56 atm) Cg = 0.0011

  18. Temperature Effects In general, the solubility of gases decreases as temperature increases

  19. Temperature Effects In general, the solubility of of ionic compounds, solids, normally increases as the temperature increases.

  20. Colligative Properties The increase or decrease of of the concentrations and not the kinds of particles in solutions can effect certain physical properties of solutions • Freezing point depression of a solution • Boiling point elevation of a solution • vapor pressure; Raoult’s Law • Osmotic pressure Colligative means “depending upon the collection”; colligative properties depend upon the collective effect of the number of solute particles

  21. Colligative Properties Lowering the Vapor Pressure: TRY EXPLAINING THIS ONE!!

  22. Lowering the Vapor Pressure: Explaining How it is Done!! A non-volatile solute added to a solvent reduces the capacity of the solvent molecules in the liquid phase to move into the gas phase The extent to which a nonvolatile solute lowers the vapor pressure is proportional to the concentration

  23. Raoult’s Law: Calculating the vapor pressure of a solution based upon the amount of solute being added to the solution. PA = XAPA° Where PA is the vapor pressure of the solution, XA is the mole fraction of solvent, and P°A is the vapor pressure of the pure solvent

  24. Colligative Properties are the first evidence that salts break up into ions. • Xa = Mole of solvent Moles of solvent + moles of solute x i If 10g of MgCl2 is added to 100ml of H2O at 23ºC, what would be the vapor pressure. The vapor pressure for water at this temperature is 21.07 torr.

  25. What is the vapor pressure of a solution made with 1 mol of Benzene and 2 mol of toluene at 20ºC and the mole fraction of the vapor? Benzene = 75 torr and Toluene = 22 torr P A = XA P°A + P B = XB P°B

  26. Properties of Solutions:Boiling Point Elevation and Freezing Point Depression

  27. Boiling Point Elevation and Freezing Point Depression Because nonvolatile solutes lower the vapor pressure of a solution, a higher temperature is required to cause the solution to boil. Because the vapor pressure of the solution is lower than that of the solvent at all temps, in accordance to Raoult’s Law, the higher temperature is required to attain a vapor pressure of 1 atm.  Tb = Kbm , where  Tb is directly proportional to the number of solute particles per moles of solvent molecules, and Kb is called the molal boiling-point-elevation constant For example, the Kb of water is 0.52 °C/m; therefore a 1m solution of sucrose or any other aqueous solution that is 1m in nonvolatile solute particles will boil at a temperature of 0.52°C higher than pure water.

  28. The freezing point corresponds to the temperature at which the vapor pressures of the solid and liquid phases are the same. The freezing point of a solution is lowered because the solute is not normally soluble in the solid phase of the solvent If the solute is nonvolatile, the vapor pressure of the solution is reduced in proportion to the mole fraction of solute.  Tf = Kfm , where  Tf is directly proportional to the number of solute particles per moles of solvent molecules, and Kf is called the molal-freezing-point-depression constant For example, the Kf of water is 1.86 °C/m; therefore a 0.5 m solution of NaCl or any other aqueous solution that is 1m in nonvolatile solute particles will freeze at a temperature of 1.86 °C lower than pure water.

  29. Calculate the freezing point and the boiling point of a solution of 100 g of ethylene glycol (C2H6O2), antifreeze in 900 g of H2O. Moles C2H6O2 100 g C2H6O2 1 mol C2H6O2 = m = .900 kg H2O Kilograms H2O 62.0 g C2H6O2 = 1.79 m = 3.33 °C (1.79 m ) = 1.86 °C  Tf = Kfm m Therefore freezing point = -3.33 °C = .52 °C  Tb = Kbm = 100.93 °C (1.79 m ) m

  30. Adrenaline is the hormone that triggers the release of extra glucose molecules in times of stress or emergency. A solution of 0.64 g of adrenaline in 36.0 g of CCl4 elevates the boiling pt. by 0.49ºC. What is the molar mass? • ΔTb = Kbm KBfor adrenaline is 3.63 • 0.49 = 3.63 (.64g mole ) xg .036kg

  31. Properties of Solutions:Osmosis The pressure required to prevent osmosis is called the osmotic pressure, , of the solution, where  = MRT The net movement of solvent is always toward the more concentrated solution

  32. Hypertonic Solution Hypotonic Solution Properties of Solutions:Osmosis

  33. Properties of Solutions:Osmosis Sample problem: The average osmotic pressure of blood is 7.7 atm. At 25°C. What concentration of glucose (C6H12O6) would be isotonic with blood?

  34. Lysozyme is an enzyme that breaks bacterial cell walls. a solution containing 0.150 g of this enzyme in 210 mL of solution has an osmotic pressure of 0.953 torr at 25ºC. What is the molar mass of Lysozyme? π = MRT .953 = .150g mole 62.3 298 xg .21L

  35. Properties of Solutions:Colloids Suspensions that are the dividing Line Between Solutions and Heterogeneous Mixtures Tyndell effect: a scattering of light by colloidal particles

  36. Properties of Solutions:Colloids The most important colloids are those in which the dispersing medium is water Hydrophilic and Hydrophobic Colloids Hydrophilic colloids are kept in suspension by interaction with surrounding water molecules

  37. Properties of Solutions:Colloids The most important colloids are those in which the dispersing medium is water Hydrophilic and Hydrophobic Colloids Hydrophobic colloids can be stabilized in water by the adsorption of ions onto their surface

  38. Properties of Solutions:Colloids The most important colloids are those in which the dispersing medium is water Hydrophilic and Hydrophobic Colloids

  39. Pa = Xa Paº Xa= moles of solvent moles of solvent + moles of solute x i ΔTb = Kbm i ΔTf = Kfm i π = MRTi

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