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Chapter 9

Chapter 9. Solutions and Colloids. Solution or Colloid. Group these? Marshmallows Wine Air Clouds Smoke Automobile oil Milk of magnesia. Colloids and Solutions. What is the difference in appearance? (Can be observed). Characteristics of Solutions. Appearance

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Chapter 9

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  1. Chapter 9 Solutions and Colloids

  2. Solution or Colloid • Group these? • Marshmallows • Wine • Air • Clouds • Smoke • Automobile oil • Milk of magnesia

  3. Colloids and Solutions • What is the difference in appearance? (Can be observed)

  4. Characteristics of Solutions • Appearance • Distribution of Particles • Separation of Components • Variable Compositions Can Be Made

  5. Colloids • particle diameter is between 1nm and 1000 nm • Colloid particles have very large surface areas, which accounts for these two characteristics of colloidal systems • they scatter light and, therefore, appear turbid, cloudy, or milky • they form stable dispersions; that is, they do not settle out

  6. Types of Solutions • Solvent: • Solute:

  7. Types of Colloids

  8. Colloids • Tyndall effect: a characteristic of colloids in which light passing through the colloid scatters • examples of colloids that exhibit the Tyndall effect are smoke, serum, and fog

  9. Properties of Mixtures

  10. Colloids and Solutions • What is the cause of the differences? (What do we think is going on?) • Video Link Changing a colloidal suspension into a solution with acid.

  11. Definitions • Solubility: • those compounds with low solubility are said to be insoluble, • those compounds with higher solubility are said to be soluble

  12. More Definitions • saturated solution: • unsaturated solution: • supersaturated solution: • Link to Video

  13. Soluble or Insoluble • Explain why some substances are soluble and other substances are not soluble by giving one example of each. Used balanced equations in you discussion. • You may use the solubility rules page 161

  14. Solvation • What happens when substances dissolve? What forces are involved? Use water as a solvent for specific examples. • Ionic? • Covalent?

  15. Water as a Solvent • How water dissolves ionic compounds • water is a • ions

  16. Water as a Solvent • How water dissolves molecular compounds • nonpolar covalent molecules • polar covalent molecules dissolve because • Each individual molecule is

  17. Electrolytes Video Link-electrolytes and non-electrolytes Video Link – Weak and strong electrolytes

  18. Electrolytes • cations migrate to the negative electrode (the cathode) • anions migrate to the positive electrode (the anode) • the movement of ions constitutes an electric current • electrolyte: • nonelectrolyte • strong electrolyte: • weak electrolyte:

  19. Stoichiometry • How can we count particles in a solution?

  20. Percent Composition • Percent composition: • weight of solute per volume of solution (w/v); • a solution of 10 g of table sugar in 100 mL of solution, for example, has a concentration of 10 percent w/v • weight of solute per weight of solution (w/w); • essentially the same as w/v except that the weight of the solution is used instead of its volume • volume of solute per volume of solution (v/v); • example, a solution of 40 mL of ethanol in 100 mL of aqueous solution is 40 percent v/v

  21. Molarity • Molarity: moles of solute per liter of solution • example: tell how to prepare 2.0 L of 0.15 M NaOH • first we find the number of moles of NaOH required • next convert 0.30 mol NaOH to g NaOH

  22. 4.5

  23. What mass of KI is required to make 500. mL of a 2.80 M KI solution? moles of solute M = molarity = liters of solution volume KI moles KI grams KI Solution Stoichiometry The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. M KI M KI 4.5

  24. Molarity • problem: the concentration of NaCl in blood serum is approximately 0.14 M. What volume of serum contains 2.0 g of NaCl? • first find the number of moles NaCl in 2.0 g NaCl • next find the volume in liters that contains this many moles of NaCl

  25. Molarity • If we dilute a solution, the number of moles of solute remains the same; use this relationship: M1V1 = M2V2 • problem: how do you prepare 200 mL of 3.5 M aqueous solution of acetic acid if you have a bottle of 6.0 M acetic acid • first find the number of L of 6.0 M acetic acid needed

  26. Moles of solute before dilution (i) Moles of solute after dilution (f) = Dilution Add Solvent = MfVf MiVi Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. 4.5

  27. How would you prepare 60.0 mL of 0.200 M HNO3 from a stock solution of 4.00 M HNO3? MiVi = MfVf 4.5

  28. Colligative Properties • Colligative property: any property of a solution that depends on the number of solute particles, and not on the nature of the particles • We study two colligative properties • freezing-point depression • osmosis

  29. Freezing-Point Depression • One mole of any particle dissolved in 1000 grams of water lowers the freezing point of water by 1.86°C • the nature of the particles does not matter, only the number of particles • Depression of freezing point has a number of practical applications • we use NaCl and CaCl2 to melt snow and ice • we use ethylene glycol as antifreeze in automobile radiators

  30. Freezing-Point Depression • Problem: if we add 275 g of ethylene glycol, C2H6O2, per 1000 g of water in a car radiator, what will be the freezing point of the solution? • ethylene glycol is a molecular compound; it dissolves in water without dissociation • first find the number of moles of ethylene glycol • each mole lowers the freezing point by 1.86°C • the freezing point of the solution will be

  31. Freezing-Point Depression • Problem: what will be the freezing point of a solution prepared by dissolving one mole of K2SO4 in 1000 grams of water? • K2SO4 is an ionic solid and dissociates to ions when dissolved in water • one mole of K2SO4 gives three moles of ions • the freezing point is lowered by

  32. Osmosis

  33. Osmosis • semipermeable membrane: a membrane with tiny pores that are big enough to allow solvent molecules to pass through them, but not big enough to allow the passage of large solute molecules • osmosis: the movement of solvent particles through a semipermeable membrane from a region of lower solute concentration (higher solvent concentration) to a region of higher solute concentration (lower solvent concentration) • osmotic pressure: the pressure necessary to prevent osmosis • osmolarity (osmol): the molarity multiplied by the number of particles produced by each formula unit of solute

  34. Osmosis • Isotonic solutions: solutions with the same osmolarity • isotonic solution: a term used primarily in the health sciences to refer to a solution with the same osmolarity as blood plasma and red blood cells • hypotonic solution: a solution with lower osmolarity than blood plasma and red blood cells • hemolysis: the swelling and bursting of red blood cells because they cannot resist the increase in osmotic pressure when put into a hypotonic solution • hypertonic solution: a solution with higher osmolarity than red blood cells

  35. Osmosis • Problem: an 0.89 percent w/v NaCl solution is referred to as physiological saline solution. What is the osmolarity (osmol) of this solution? • 0.89 w/v NaCl = 8.9 g in 1 L of solution • first we calculate the number of moles of NaCl in this solution • because each mole of NaCl dissolved in water dissociates into two ions, the osmolarity of the solution is

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