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Properties of Solutions

Properties of Solutions. Terminology. Solution = A homogeneous mixture. Solute = a substance dissolved in a solvent to form a solution; usually the smaller portion. Solvent = The dissolving medium of a solution; usually the greater portion. Solubility = Amount of substance dissolved.

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Properties of Solutions

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  1. Properties of Solutions

  2. Terminology • Solution = A homogeneous mixture. • Solute = a substance dissolved in a solvent to form a solution; usually the smaller portion. • Solvent = The dissolving medium of a solution; usually the greater portion. • Solubility = Amount of substance dissolved. • Dilute , Concentrated , Saturated .

  3. The Solution Process

  4. Figure 13.2: The Solution Process Hydration or Solvation

  5. The Solution Process Solution Formation, Spontaneity, and Disorder • If the process leads to a greater state of disorder, then the process is spontaneous. • Example: a mixture of CCl4 and C6H14 is less ordered than the two separate liquids. Therefore, they spontaneously mix even though Hsoln is very close to zero. • There are solutions that form by physical processes and those by chemical processes.

  6. Factors Affecting Solubility Solute-Solvent Interaction • Miscible liquids: mix in any proportions. • Immiscible liquids: do not mix. [ Oil and Vinegar ] • Generalization: “like dissolves (in) like”. • Polar liquids/substances tend to dissolve in polar solvents. • Nonpolar substances tend to dissolve in nonpolar solvents.

  7. Ways of Expressing Concentration Mass Percentage • All methods involve quantifying amount of solute per amount of solvent (or solution). • Generally amounts or measures are masses, moles or liters.

  8. Ways of Expressing Concentration • Mole Fraction, Molarity, and Molality

  9. Solution Compositions • s = solute ; A = solvent; V = Tot. Vol. of solution. • Weight %: • Mole Fraction: • Molarity: • Molality:

  10. Example of Solution Compositions • A solution is prepared by mixing 78.9 g of ethanol (C2H5OH) with 100.0 g of water to give 190.5 mL of solution. Calculate the solution compositions. • The electrolyte in automobile lead storage batteries is a 3.75 M H2SO4 solution that has a density of 1.230 g/mL. Calculate mass %, molality, and mole fraction in terms of H2SO4 . • [Hint: Assume exactly one liter of solution.] • [Answers: 29.9% , 4.35 molal, 0.0727 ]

  11. s = ethanol (solute); A = water (solvent);

  12. Concentrations of Solutions In the Dilution process of a more concentrated solution: • The number of moles are the same in diluted and concentrated solutions. • So: MdiluteVdilute = moles = MconcentratedVconcentrated

  13. Video Question: ( Mi Vi = Mf Vf ) How many mL of the stock solution of 1.000 M CuSO4 solution do you need to make 250. mL of a 0.1000 M CuSO4 solution?

  14. General Properties of Aqueous Solutions Electrolytic Properties • Three types: • Strong electrolytes, • Weak electrolytes, and • Nonelectrolytes.

  15. General Properties of Aqueous Solutions Strong and Weak Electrolytes • Strong electrolytes: completely dissociated in solution. e.g. • Weak electrolytes: produce small concentration of ions when dissolved. • e.g.

  16. Precipitation Reactions

  17. Precipitation Reactions Exchange (Metathesis) Reactions • Metathesis reactions involve swapping ions in solution: AX + BYAY + BX.

  18. Precipitation Reactions Ionic Equations • Ionic equation: used to highlight reaction between ions. • Molecular equation: all species listed as molecules: AgNO3(aq) + NaI(aq)  AgI(s) + NaNO3(aq) • Complete ionic equation(CIE): lists all ions: Ag+(aq) + NO3-(aq) + Na+(aq) + I-(aq)  AgI(s) + Na+(aq) + NO3-(aq) • Net ionic equation: cancel spectator ions from CIE Ag+(aq) + I-(aq)  AgI(s)

  19. Figure 13.14: Factors Affecting Solubility • Intermolecular Forces • Pressure • Temperature

  20. Figure 13.14: Factors Affecting Solubility Pressure Effects

  21. Factors Affecting Solubility Pressure Effects • If Sg is the solubility of a gas, k is a constant, and Pg is the partial pressure of a gas, then Henry’s Law gives: • Carbonated beverages are bottled with a partial pressure of CO2 >1 atm, ( pressure inside can ~4 atm above liq). • As bottle is opened, partial pressure of CO2 decreases and solubility of CO2 decreases. • Therefore, bubbles of CO2 escape from solution. CyberChem Diving Gases

  22. Factors Affecting Solubility Temperature Effects: Solids in Liquids • Generally, as temperature increases, solubility of solids generally increases, BUT • Sometimes, solubility decreases as temperature increases (e.g. Ce2(SO4)3).

  23. Figure 13.18

  24. Factors Affecting Solubility Temperature Effects: Gases in Liquids • Gases get less soluble as temperature increases. • Thermal pollution: if lakes get too warm, CO2 and O2 become less soluble and are not available for plants or animals.

  25. Figure 13.18

  26. Colligative Properties • Colligative properties depend on quantity of solute molecules. (e.g. freezing point depression and boiling point elevation.) Lowering Vapor Pressure • Non-volatile solutes reduce the ability of the surface solvent molecules to escape the liquid. • Therefore, vapor pressure is lowered. • The amount of vapor pressure lowering depends on the amount of solute.

  27. Figure 11.22: Vapor Pressure Vapor Pressure on the Molecular Level

  28. Figure 11.24

  29. Figure 11.26: Phase Diagrams

  30. Figure 11.27: Phase Diagrams The Phase Diagrams of H2O and CO2

  31. Figure 13.20: Colligative Properties Lowering Vapor Pressure

  32. Colligative Properties Lowering Vapor Pressure • Raoult’s Law: • Where: PA = vapor pressure with solute, • PA = vapor pressure without solute (pure solvent), and • A = mole fraction of A.

  33. Vapor Pressure Examples • Calculate the expected vapor pressure at 25oC for a solution prepared by dissolving 158.0 g of common table sugar (sucrose – MW=342.3) in 643.5 mL of water. At 25oC, the density of water is 0.9971 g/mL and the vapor pressure is 23.76 torr. • A solution was prepared by adding 20.0 g of urea to 125 g of water at 25oC, a temperature at which pure water has a vapor pressure of 23.76 torr. The observed vapor pressure of the solution was found to be 22.67 torr. Calculate the molecular weight of urea. [Answer: 60. g/mol ]

  34. Calculate the expected vapor pressure at 25oC for a solution prepared by dissolving 158.0 g of common table sugar (sucrose – MW=342.3) in 643.5 mL of water. At 25oC, the density of water is 0.9971 g/mL and the vapor pressure is 23.76 torr.

  35. Figure 13.22

  36. Colligative Properties • Boiling-Point Elevation • Molal boiling-point-elevation constant, Kb, expresses how much Tb changes with molality, mS: • Decrease in freezing point (Tf) is directly proportional to molality (Kfis the molal freezing-point-depression constant):

  37. Colligative Properties

  38. Applications of Colligative Properties • A solution was made by dissolving 18.00 g of glucose in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34oC. Calculate the molecular weight of glucose. • How many kg of ethylene glycol (C2H6O2, MW=62.1), antifreeze, must be added to 10.0 L of water to produce a solution for use in a car’s radiator that freezes at –23.3oC? Assume that the density of water is 1.00 g/mL. [Answer: 7.78 kg (with d = 1.18 g/mL => 6.59 L)]

  39. A solution was made by dissolving 18.00 g of glucose in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34oC. Calculate the molecular weight of glucose. 1.8x102 g/mol

  40. How many kg of ethylene glycol (C2H6O2, MW=62.1), antifreeze, must be added to 10.0 L of water to produce a solution for use in a car’s radiator that freezes at –23.3oC? Assume that the density of water is 1.00 g/mL.

  41. Colligative Properties: Homework due for Friday Dec. ?, 201?. What is the molecular weight (g/mol) of a non-volatile solute if 7.32 kg of this solute dissolved in 10.0 L of water produced a solution with a freezing point of -23.3C? Assume density of water as 1.00 g/mL.

  42. Colligative Properties Osmosis • movement of a solvent from low solute concentration to high solute concentration across a semipermeable membrane. Figure 13.23

  43. Colligative Properties Osmosis • Osmotic pressure, , is the pressure required to stop osmosis:

  44. Application of Osmotic Pressure • To determine the molecular weight of a certain protein, 1.00 mg of it was dissolved in enough water to make 1.00 mL of solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0oC. Calculate the molecular weight of the protein. [Answer: 1.66x104 g/mol]

  45. To determine the molecular weight of a certain protein, 1.00 mg of it was dissolved in enough water to make 1.00 mL of solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0oC. Calculate the molecular weight of the protein.

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