Understanding Solutions and Colloids: Characteristics, Types, and Properties

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