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Chapter 7: Solutions and Colloids

Chapter 7: Solutions and Colloids. Suggested Problems : 4, 16, 20-28, 46, 48, 52-56, 64, 66, 72, 74, 92. What is a Solution?.

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Chapter 7: Solutions and Colloids

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  1. Chapter 7: Solutions and Colloids Suggested Problems: 4, 16, 20-28, 46, 48, 52-56, 64, 66, 72, 74, 92

  2. What is a Solution? • A solution is a homogeneous mixture comprised of one or more solutes dispersed at an atomic, ionic or molecular level uniformly throughout a medium called the solvent • Solvent: Is the most abundant substance in a solution • Solute: Are all of the other components that comprise the solution • Notice I did not say dissolved in the solvent

  3. Importance of Solutions • Most medicines are given as solutions • Most chemistry occurs in solution, rather than in a pure state • Focus of this chapter • Solution concentrations • Properties of solutions

  4. Describing Solutes • Solubility: The maximum amount of solute than can be dissolved in a specific amount of solvent under specific conditions of temperature and pressure • Soluble Substance: is a substance that dissolves to a significant extent in the solvent • Insoluble Substance: A substance that does not dissolve to a significant extent in a solvent • Immiscible: A term used to describe liquids that are insoluble in each other

  5. Describing Solutions • Saturated: A solution that has the maximum amount of solute dissolved in a given amount of solvent • Super Saturated: A solution that has a solute dissolved at a greater amount than the solubility of that solute

  6. Process of Solution Formation • Ionic Solutes: Need Polar solvent • IMF’s between solute/solvent > solute/solute

  7. Process of Solution Formation • Molecular Solutes: Need proper solvent Polar if Polar solute Non-polar if Non-polar solute Dissolved gases: O2, N2

  8. Solution Concentrations: Percent Definitions

  9. Beware of question wording • If solute is added to enough solvent to make a solution of a certain volume • This volume is the volume of solution • If problem states a volume of solute is added to a volume of solvent • Then you need to add the two volumes to get volume of solution

  10. Remember that percentages are best used if based out of a total of 100 • This is true whether it be mass or volume • For example a 5 % (w/v) solution • This is the same as saying:

  11. Percent Example • What is the percent (w/v) concentration of a solution prepared by dissolving 45 grams of glucose in enough water to give 300.0 mL of solution?

  12. Percent Example • Normal saline is 0.89% (w/v) NaCl in water. What volume of normal saline is required to deliver 45 grams of NaCl?

  13. Percent Example • D-5-W is 5.0% (w/v) dextrose in water. How many grams of dextrose are contained in 1500.0 mL D-5-W?

  14. Solution Concentrations: Molarity • Useful unit in dealing with chemicals in solution

  15. Molarity Example • What is the molarity of a solution prepared by dissolving 58.5 grams of Cu(NO3)2 in enough water to give a total volume of 500.0 mL?

  16. Molarity Example • How many moles of HCl are contained in 750.0 mL of a 2.5 M solution?

  17. Titration • A titration is a chemical analysis that uses volume and molarity • In simple acid-base titrations, you can use this equation*: MacidVacid= MbaseVbase • *must be a 1:1 stoichiometric reaction or else this equation does not work

  18. Titration Example • A 25 mL sample of vinegar (which contains acetic acid) is titrated with 0.100 M NaOH. If 6.75 mL of NaOH are required, what is the molarity of the acetic acid in vinegar? 0.100 M NaOH 25 mL of vinegar

  19. Dilutions • Many reagents and medicines are available as “stock” solutions that must be diluted prior to use • In any dilution, you can always use this equation: C1V1=C2V2 C = concentration V = volume

  20. Example • If 8.33 mL of 12 M HCl are diluted with water to give a new volume of 1000.0 mL, what is the molarity of the resulting solution?

  21. Example • How many mL of 5.0% NaCl solution are needed to prepare 5.0 Liters of normal saline?

  22. Electrolytes • Strong electrolytes dissolve 100% in water to afford solutions that conduct electricity • Soluble ionic compounds • Strong acids (HCl, H2SO4, HNO3)

  23. Weak Electrolytes • Weak electrolytes dissociate less than 100% into ions when dissolved in water and produce solutions with varying ability to conduct electricity • Weak Acids (H3PO4, HF, H2S)

  24. Non-Electrolytes • When molecular compounds (covalently bonded compounds) dissolve in water, no ions are produced, so the solution does not conduct electricity

  25. Colligative Properties of Solutions • Colligative properties are those properties that depend on the concentration of the solute, not the identity of the solute • Examples: • Electrical Conductivity • Vapor Pressure • Boiling Point • Freezing Point

  26. Freezing Point Depression • The freezing point of a solution goes down as the concentration of solute increase • Should use molality

  27. Freezing Point Depression Example • Calculate the freezing point of a solution comprised of 171 g of C12H22O11 dissolved in enough water to have a final volume of 1.00 L.

  28. Boiling Point Elevation • The boiling point of a solution increases as the concentration of solute increases • Should use molality

  29. Boiling Point Elevation Example • If 13.4 g of NH4Cl is dissolved in water to form a 500.0 mL solution, what is the new boiling point of this solution, assuming that water boils at 100 oC?

  30. Osmotic Pressure • The osmotic pressure of a solution increases as the concentration of solute increases

  31. Diffusion • Diffusion is the movement of a substance from an area of high concentration to an area of low concentration

  32. Osmosis • Osmosis is diffusion of water through a semipermeable membrane • Solute particles are too big (or too polar) to make it across the membrane • This is how water gets moved around cells

  33. Hydrostatic Pressure • As the water level rises so does the hydrostatic pressure against the membrane, until a pressure is reached that causes the net movement of water to equilibrate and the volume levels of the two sides become constant

  34. Osmotic Pressure • Osmotic Pressure () is the hydrostatic pressure required to stop the flow of a solvent from low concentration to high concentration  =nMRT n = moles of particles obtained when one mole of solute dissolves M= molarity of the solution R = is the ideal gas constant T = the temperature in Kelvin nM = Osmolarity, a term used in biology and medicine

  35. Tonicity • Isotonic solutions have equal concentrations of solute particles • A hypertonic solution has a greater concentration of solute • A hypotonic solution is a lower concentration of solute

  36. Example Hypertonic solution Less water Hypotonic solution More water Cl- Na+ Na+ Cl- Direction of osmosis H2O H2O SPM Which direction will the water diffuse?

  37. Question • What will happen to a red blood cell when it is placed into pure water? Cells are isotonic with normal saline (0.89% NaCl). Hint: think about the flow of H2O. • Hemolysis

  38. Question • What will happen to a red blood cell when it is placed into 10% aqueous sodium chloride? Cells are isotonic with normal saline (0.89% NaCl)

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