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Solutions

Explore solutions, suspensions, and colloids, solvents, solutes, and electrolytes. Learn about the factors influencing dissolution rates and concentrations. Practice molarity calculations and understand saturation concepts.

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Solutions

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  1. Solutions From Chapters 12 and 13

  2. Reading • Chapter 12 • Section 1 (pp. 363-366) • Section 4 (pp. 384-385) • Chapter 13 • all (pp.395-418)

  3. Solutions • homogenous mixture • 2 parts 1. solute - dissolved 2. solvent - does dissolving (greatest amount)

  4. Solution examples

  5. The Universal Solvent Water H2O • a part of almost every liquid on earth • shape – bent • polar • high surface tension • capillary action • hydrogen bonding

  6. Distinguish between… soluble • if it will dissolve miscible • liquids that will dissolve in one another insoluble • if it will NOTdissolve immiscible • liquids that will NOTdissolve in one another

  7. Types of solutions

  8. 1. solid solutions • alloys – two or more solids evenly mixed • steel, brass • amalgam – an alloy containing mercury • uses in dentistry, gold extraction, industry

  9. 2. gas solutions • gas dissolved in gas • i.e. air • oxygen and other gases dissolved in nitrogen

  10. 3. liquid solutions • aqueous solutions • solvent is water • tincture solutions • solvent is alcohol • tincture of iodine miscible/immiscible

  11. “like dissolves like” • solvation – interaction of solute and solvent • polar solvents dissolve polar and ionic substances • non-polar solvents dissolve non-polar substances

  12. hydrate • when a compound contains water i.e. • hydrated copper sulfate • CuSO4 ∙ 5H2O • copper sulfate pentahydrate

  13. Suspensions • particles are larger than in solutions • particles evenly distributed by a mechanical means (i.e. shaking the contents) • BUT the components will settle out.

  14. Suspension Examples • mud, muddy water • paint • flour suspended in water • dust in air • algae in water

  15. Colloids • particles intermediate in size between solutions and suspensions • microscopically evenly distributed without settling out • ‘colloidal particles’ or colloids • ‘colloidal dispersion’ • A colloidal dispersion consists of colloids in a dispersing medium. • Liquids, solids, and gases all may be mixed to form colloidal dispersions.

  16. Colloid Examples • Aerosols: solid or liquid particles in a gas. • Examples: Smoke is a solid in a gas. Fog is a liquid in a gas. • Sols: solid particles in a liquid • Example: Milk of Magnesia is a sol with solid magnesium hydroxide in water. • Emulsions: liquid particles in liquid. • Example: Mayonnaise is oil in water. • Gels: liquids in solid. • Examples: gelatin is protein in water. Quicksand is sand in water.

  17. How to tell apart? • suspension particles will separate • colloids display Tyndall Effect • Tyndall effect - Light passing through a colloidal dispersion will be reflected by the larger particles and the light beam will be visible • solutions will not separate or scatter light

  18. Electrolytes • if something conducts electricity in solution – electrolyte • if not – non-electrolyte • if it conducts a little electricity – weak electrolyte

  19. Factors Affecting Rate of Dissolving • nature of the solute and solvent

  20. Factors Affecting Rate of Dissolving • temperature • higher temperature, more solute can go into solution • gases are opposite

  21. Factors Affecting Rate of Dissolving • pressure • increased pressure increases gas solubility • doesn’t affect liquids or solids

  22. Factors Affecting Rate of Dissolving • particle size • smaller particles dissolve faster • ‘increase surface area’

  23. Factors Affecting Rate of Dissolving • agitation • stirring increases rate of dissolution

  24. Henry’s Law • at a given temperature, the solubility of a gas in a liquid (S) is directly proportional to the pressure of a gas above the liquid (P) S1 = S2 P1 P2

  25. Solution concentration • solubility • the amount of solute dissolved in a given solvent at a specific temperature • i.e. solubility of sugar is 204 g per 100. g of water at 20 C • concentration • amount of solute in a given amount of solvent or solution • measured in molarity (mol/L) or molality (mol/kg)

  26. Saturation • saturated • maximum solubility • solution holds as much solution as possibleunder given conditions (T&P) • unsaturated • less than maximum • supersaturated • greater than maximum • grows crystals • i.e. rock candy

  27. Relative concentration • concentrated – large amount of solute in small amount of solvent • dilute – small amount of solute in large amount of solvent • relative amounts, depends on what you compare it to

  28. Molarity molarity (M) M = moles of solute liters of solution unit - mol/L M1V1 = M2V2

  29. Examples • A saline solution contains 0.90g NaCl per 100 mL of solution. What is its molarity? • A salt solution has a volume of 250 mL and contains 0.70 mol of NaCl, what is the molarity? • How many moles of solute are present in 1.5 L of 0.2 M Na2SO4?

  30. Examples • What volume of MgSO4 is needed to prepare 100 mL of 0.4M solution from a 2.0 M solution? • You need 250 mL of 0.20 M NaCl, but you only have a 1.0 M solution of sodium chloride, what do you do?

  31. % solution • % by volume • volume solute/volume solution x 100 • % by mass/volume • mass of solute/volume of solution x 100 • g and mL • ppm – number of grams per million grams

  32. Examples • What is the percent by volume of ethanol (C2H6O) in the final solution when 75 mL of ethanol is diluted to a volume of 250 mL with water? • How many grams of glucose would you need to prepare 2.0L of 2.0% sucrose (m/v) solution?

  33. Mixed Review • A solution contains 2.7 g of CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution? • How many moles of solute are in 250 mL of 2.0 M CaCl2? How many grams of CaCl2 is this? • How many grams of magnesium sulfate are required to make 250 mL of a 1.6% MgSO4 (m/v) solution

  34. Mixed Review • If 10 mL of acetic acid is diluted with 190 mL of water, what is the percent by volume of the acetic acid? • An aqueous solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g, what is the molarity of the solution?

  35. Class work • In grey books • pg 390 • #26, 27, 28 (a-c), 30(a-b), 31 (a-b), 33 your books - pg 942 #367-373 Homework

  36. Molality molality (m) m = moles solute kg solvent unit: mol/kg

  37. Examples • How many grams of potassium iodide must be dissolved in 500. g of water to produce 0.060 molal KI solution? • Calculate the molality of a solution prepared by dissolving 10.0 g of NaCl in 600.g of water.

  38. mole fraction number of moles of one component divided by total number of moles of solution • represented by Xx Xsolute = moles of solute moles of solution Xsolvent = moles of solvent moles of solution Xsolute +Xsolvent 1

  39. Examples • Compute the mole fraction of each component in a solution of 1.25 mol ethylene glycol (EG) and 4.00 mol water. • What is the mole fraction of each component in a solution made by mixing 300. g of ethanol and 500. g of water? • A solution is labeled 0.150 molalNaCl.What are the mole fractions of the solute and the solvent in this solution?

  40. Class work • In your blue books • pg 421 • 15b, 16, 17, 19c, 23, 24, 26, 28, 29, 32 • Homework: pg 941 • 338-340, 350, 352, 365

  41. Colligative Properties *note: colligative properties will be bonus questions on the test. • property that depends on concentration • 4 types • vapor pressure reduction • boiling point elevation • freezing point depression • osmotic pressure

  42. vapor pressure reduction • vapor pressure over a solvent is reduced when a solute is dissolved in the solvent

  43. boiling point elevation • amount by which the boiling point is raised when a solute is in solution • ∆Tb = Kbm(i) • Kb – molal boiling point constant • m – molality • (i)Van’t Hoff factor

  44. freezing point depression • a dissolved solute lowers the freezing point • ∆Tf = Kfm(i) • Kf – freezing point depression constant • m – molality • (i)Van’t Hoff factor

  45. osmotic pressure • pressure required to prevent osmosis • osmosis – net flow of solvent molecules from less concentrated solution to more concentrated solution

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