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Chapter 7: Solutions and Colloids Suggested Problems: 4, 16, 20-28, 46, 48, 52-56, 64, 66, 72, 74, 92
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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
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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
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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
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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
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Process of Solution Formation Ionic Solutes: Need Polar solvent IMF’s between solute/solvent > solute/solute
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Process of Solution Formation Molecular Solutes: Need proper solvent Polar if Polar soluteNon-polar if Non-polar solute Dissolved gases: O 2, N 2
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Solution Concentrations: Percent Definitions
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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
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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:
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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?
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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?
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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?
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Solution Concentrations: Molarity Useful unit in dealing with chemicals in solution
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Molarity Example What is the molarity of a solution prepared by dissolving 58.5 grams of Cu(NO 3 ) 2 in enough water to give a total volume of 500.0 mL?
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Molarity Example How many moles of HCl are contained in 750.0 mL of a 2.5 M solution?
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Titration A titration is a chemical analysis that uses volume and molarity In simple acid-base titrations, you can use this equation*: M acid V acid = M base V base *must be a 1:1 stoichiometric reaction or else this equation does not work
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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? 25 mL of vinegar 0.100 M NaOH
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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: C 1 V 1 =C 2 V 2 C = concentration V = volume
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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?
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Example How many mL of 5.0% NaCl solution are needed to prepare 5.0 Liters of normal saline?
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Electrolytes Strong electrolytes dissolve 100% in water to afford solutions that conduct electricity –Soluble ionic compounds –Strong acids (HCl, H 2 SO 4, HNO 3 )
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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 (H 3 PO 4, HF, H 2 S)
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Non-Electrolytes When molecular compounds (covalently bonded compounds) dissolve in water, no ions are produced, so the solution does not conduct electricity
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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
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Freezing Point Depression The freezing point of a solution goes down as the concentration of solute increase Should use molality
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Freezing Point Depression Example Calculate the freezing point of a solution comprised of 171 g of C 12 H 22 O 11 dissolved in enough water to have a final volume of 1.00 L.
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Boiling Point Elevation The boiling point of a solution increases as the concentration of solute increases Should use molality
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Boiling Point Elevation Example If 13.4 g of NH 4 Cl 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 o C?
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Osmotic Pressure The osmotic pressure of a solution increases as the concentration of solute increases
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Diffusion Diffusion is the movement of a substance from an area of high concentration to an area of low concentration
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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
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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
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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
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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
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Example Na + H2OH2OH2OH2O H2OH2OH2OH2O Cl - Hypertonic solution Less water Na + H2OH2OH2OH2O H2OH2OH2OH2O Cl - Hypotonic solution More water Direction of osmosis SPM Which direction will the water diffuse?
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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 H 2 O. Hemolysis
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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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