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Properties of Solutions

Properties of Solutions. 11.5-11.8. Boiling-Point Elevation and Freezing-Point Depression. Colligative Properties. Properties that are ONLY dependent on the number of solute particles Not dependent on their identity Examples Boiling-point elevation Freezing-point depression

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Properties of Solutions

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  1. Properties of Solutions 11.5-11.8

  2. Boiling-Point Elevation and Freezing-Point Depression

  3. Colligative Properties • Properties that are ONLY dependent on the number of solute particles • Not dependent on their identity • Examples • Boiling-point elevation • Freezing-point depression • Osmotic pressure

  4. Boiling-Point Elevation • Nonvolatile solutes elevate the boiling-point of the solvent • ΔT= Kbmsolute • ΔT - boiling point elevation • Kb - the molal boiling point elevation constant of the solvent • msolute – the molality of the solute in the solutions

  5. Freezing-Point Depression • Solutes depress the freezing point of the solvent • ΔT= Kfmsolute • ΔT - freezing point depression • Kf - the molal freezing point depression constant of the solvent • msolute – the molality of the solute in the solutions

  6. Osmotic Pressure • Osmosis – flow of solvent molecules into a solution through a semi-permeable membrane • Small concentration of solute produces a relatively large osmotic pressure

  7. Osmotic Pressure • The pressure necessary to keep water from flowing across a semi-permeable • Osmotic pressure can be used to characterize solutions and determine molar masses • π = MRT • π – osmotic pressure in atmospheres • M – molarity of the solution • R – gas law constant • T – Kelvin temperature

  8. Osmosis • Dialysis – transfer of solvent molecules as well as small solute molecules and ions • Isotonic Solutions – solutions that have the same osmotic pressure • Osmotic Pressure in Living Cells • Crenation – cells placed in a hypertonic solution lose water to the solution and shrink • Hemolysis – cells placed in a hypotonic solution gain water from the solution and swell, possibly bursting

  9. Reverse Osmosis • External pressure applied to a solution can cause water to leave the solution • Concentrates impurities (salt) in the remaining solution • Pure solvent (water) is recovered on the other side of the semi-permeable layer

  10. Colligative Properties of Electrolyte (Ionic) Solutions

  11. van’t Hoff Factor (i) • van’t Hoff Factor (i) – the relationship between the moles of solute dissolved and the moles of particles in solutioni = moles of particle in soln moles of solute dissolved • For ionic compounds, the expected value of i is an integer greater than 1 • NaCl – 2, BaCl2 – 3, etc.

  12. van’t Hoff Factor (i) • Values of i are less than expected due to ion pairing • Ion pairing – phenomenon occurring in solution when oppositely charged ions aggregate and behave as a single particle • Closer to expected values in more dilute solutions

  13. van’t Hoff Factor (i) • Incorporating the van’t Hoff • Boiling point/freezing point • ΔT = imK • Osmotic Pressure • π = iMRT

  14. Colloids • Colloid – suspension of particles in some medium • Particles do no precipitate out because of electrostatic repulsion • Tyndall effect – the scattering of light by particles and is used to distinguish between a suspension and a true solution • Light passes through a solution • Light is scattered in a colloid

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