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CHAPTER 14: SOLUTIONS AND THEIR PROPERTIES

CHAPTER 14: SOLUTIONS AND THEIR PROPERTIES. SOLUTION homogeneous mixture of two or more substances in a single phase. Solvent component present in the largest amount, substance doing the dissolving Solute component present in the smallest amount, the substance dissolved.

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CHAPTER 14: SOLUTIONS AND THEIR PROPERTIES

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  1. CHAPTER 14: SOLUTIONS AND THEIR PROPERTIES • SOLUTION homogeneous mixture of two or more substances in a single phase. • Solvent component present in the largest amount, substance doing the dissolving • Solute component present in the smallest amount, the substance dissolved.

  2. Quantitative ways to describe a solution, solute, solvent (moles, mass, or volume) • Molarity (M) = mole of solute/liter solution • Molality (m) = moles of solute/kg of solvent • Mole fraction (X) = nA / (nA + nB …) moles of a given component divided by the total # of moles of all components.

  3. Quantitative ways to describe a solution, solute, solvent (moles, mass, or volume) • Weight % = mass of solute/mass of solution * 100 • ppm = mg solute/l L solvent • Normality (N) = # Equivalents / L

  4. Practice • A solution is prepared by mixing 1.00 g ethanol (C2H5OH) with 100.0 g water to give a final volume of 101 mL. • Calculate the molarity, molality, mole fraction, weight %, and ppm of ethanol in this solution.

  5. Solution Process • Intermolecular forces (likes dissolve likes) • When liquids mix and form a solution they are miscible • Immiscible liquids do not mix. • Terms with solutions

  6. Solution Terms • SATURATED - A stable solution in which the maximum amount of solute has been dissolved • UNSATURATED -The concentration of solute is less than the saturated amount. • SUPERSATURATED- A solution that contains more than the saturated amount of solute Solution Diagrams

  7. How Solutions FormThermodynamics • The formation of solutions is favored because it creates a more disordered system. • If the process requires too much energy, the process will not occur. The energy can be calculated.

  8. Thermodynamicsof Solutions • For an ionic crystal, first the crystal must break apart, negative the (negative) lattice energy, therefore a positive enthalpy. • Then the ions must hydrate (be surrounded by water molecules) which has a negative enthalpy.

  9. Thermodynamicsof Solutions • Dissolve CaCl2 in water and describe the relationship between lattice energy and the energy of hydration • Dissolve NH4Cl in water and describe the relationship between lattice energy and the energy of hydration

  10. Thermodynamicsof Solutions

  11. Thermodynamicsof Solutions

  12. Thermodynamicsof Solutions

  13. Thermodynamicsof Solutions

  14. Factors Affecting Solubility Pressure and Temperature: • Gases dissolved in water demonstration • Bromothymol Blue solution and Alka-Seltzer in 200 mL DI water

  15. Factors Affecting Solubility Pressure and Temperature: • Pressure: Solubility of Gases in Liquids: • Henry's Law: Sg = k H Pg

  16. Factors Affecting Solubility Pressure and Temperature: • Solubility Diagrams

  17. Factors Affecting Solubility Pressure and Temperature:

  18. Factors Affecting Solubility Pressure and Temperature:

  19. Factors Affecting Solubility Pressure and Temperature:

  20. Colligative Properties • Changes in Vapor Pressure: Raoult’s Law • The vapor pressure over the solution is lower than the vapor pressure of pure solvent. • The vaopr pressure of the solvent Psolv is propotional to the relative number of solvent molecules in the solution, the solvent vapor pressure is proportional to the solvent mole fraction. • Colligative Properties Definitions

  21. Raoult’s Law • Psolv = Xsolv Posolv • Raoult’s Law applies to ideal solutions Roult’s Law Diagram

  22. Colligative Properties

  23. Colligative Properties • Raoult’s Law Adding a non volatile solute to a solvent lowers the vapor pressure of the solvent so the change in vapor pressure of the solvent can be calculated as a function of the mole fraction.

  24. Colligative Properties

  25. Colligative Properties

  26. Colligative Properties

  27. Colligative Properties • The boiling point of a solution is related to the solute concentration. • The boiling point elevation D Tbp is directly proportional to the molality of the solute: • D T bp = Kbp msolute • molal boiling point elevation constant has the units of degrees/molal (oC / m).

  28. Colligative Properties • What quantity of elthylene glycol, HOCH2CH2OH must be added to 125 g of water to raise the boiling point of 1.0oC? • Kbp of water is + 0.5121oC/m

  29. Colligative Properties • The freezing point of a solution is related to the solute concentration. • The freezing point depression D Tfp is directly proportional to the molality of the solute: D Tfp = Kfp msolute • molal freezing point depression constant has the units of degrees/molal (oC / m).

  30. Colligative Properties • In the northern United States, summer cottages are usually closed up for the winter. When doing so the owners “winterize” the plumbing by putting antifreeze, HOCH2CH2OH, in the toilet tanks. Will adding 525 g of anitfreeze to 3 kg of water ensure that the water will not freeze at -25oC. • Kfp of water is -1.86 oC/m

  31. Colligative Properties • Colligative Properties and Molar Mass Determination

  32. Colligative Properties • Van’t Hoff Factor i • When an ionic compound dissolves in a solvent, the number of ions determines the behavior of the solvent. • For example, 1 m NaCl will lower the f.p. of water twice as much as 1 m sugar because NaCl breaks into 2 ions

  33. Colligative Properties • Van’t Hoff Factor I Diagrams & Photo • Actually only dilute solutions behave in this manner. • Officially, i = D Tfp measured D Tfp calculated • So often the value of i approaches a whole number.

  34. Colligative Properties Osmosis is the movement of solvent molecules through a semipermeable membrane from a region of lower to a region of higher solute concentration.

  35. Colligative Properties Osmotic Pressure the pressure created by the column above the solution measured by the difference in height between the solution in the tube and the level of water in the beaker. Osmotic Terms

  36. Colligative Properties Osmotic Pressure is related to concentration. Recall the Ideal Gas Law PV = nRT Rearrange the equation so the concentration is (n/V) P = (n/V) R T Change the symbols P to P for osmotic pressure and (n/V) to c The resulting equation for Osmotic Pressure is P = c R T R = .082 L x atm mol x K

  37. Colligative Properties Osmosis isotonic similar concentrations of solutes hypotonic solution with lower solute concentrations hypotonic solution with higher solute concentrations reverse osmosis using pressure to purify water.

  38. Colligative Properties Colloids

  39. Colligative Properties Colloids are classified according to the state of dispersed phase and the dispersing medium. Hydrophobic ‘water fearing’ weak attractive forces between water and surface of colloidal particles. Hydrophilic ‘water loving’ are strongly attracted to the water molecules Emulsions are colloidal dispersions of one liquid in another by using an emulsifying agent such as protein or soap.

  40. Colligative Properties Surfactants are emulsifying agents Hydrocarbon end soluble in oil Polar end soluble in water

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