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Colligative Properties

Colligative Properties. Does solute change the properties of a solvent?. Consider aqueous solutions Solvent = water How do properties of aqueous solution compare to properties of pure water?. Conductivity. Pure water does not conduct electricity Some aqueous solutions do

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Colligative Properties

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  1. Colligative Properties

  2. Does solute change the properties of a solvent? • Consider aqueous solutions • Solvent = water • How do properties of aqueous solution compare to properties of pure water?

  3. Conductivity • Pure water does not conduct electricity • Some aqueous solutions do • To conduct current, solution must contain ions • Conductivity depends on nature of the particle • Molecular (covalent) solutes do not conduct; ionic solutes do conduct

  4. Colligative Properties • Depend on number particles in solution not on type particles • i.e. doesn’t matter what kind of particles: can be ions or molecules • Concentration of particles doesmatter

  5. What are some colligative properties? • Vapor Pressure (↓) • Freezing Point (↓) • Boiling Point (↑) • change in Osmotic Pressure • higher the concentration of solute particles, the larger the effect

  6. Does it matter if solute is ionic or covalent? • number of particles will vary • Ionic solutes • dissolve to produce (+) & (-) ions more particles per mole of solute • Covalent solutes • 1-to-1relationship betweenmoles of solute and moles of dissolved particles

  7. C6H12O6 • Covalent substances: • dissolve as molecules: C6H12O6(s)+ H2O(l)  C6H12O6(aq) 1 mole sugar → 1 mole molecules

  8. NaCl • Ionic substances: • dissolves (dissociates) as ions: NaCl(s) + H2O(l)  Na+1(aq) + Cl-1(aq) 1 mole salt  2 moles ions

  9. MgCl2 • Ionic substance: • dissolves as ions MgCl2(s) + H2O(l)  Mg2+(aq) + 2Cl-(aq) 1 mole salt 3 moles ions

  10. As solute is added to a solvent, what happens to freezing point & boiling point of solution? • The freezing point ↓ & the boiling point ↓ • The freezing point ↓ & the boiling point ↑ • The freezing point ↑ & the boiling point ↓ • The freezing point ↑ & the boiling point ↑ Answer: 2

  11. Which solution containing 1 mole of solute dissolved in 1000 g of water has the lowest freezing point? • C2H5OH(aq) • NaCl(aq) • KOH • CaCl2 Be careful! - do you want greatest or least change? What if question asked which solution has highest freezing point? Answer: 4

  12. Of the following solutions, the one that will freeze at the lowest temperature contains 1 mole of nonvolatile solute dissolved in 1) 250 g of solvent 2) 500 g of solvent 3) 750 g of solvent 4) 1000 g of solvent Answer: 1

  13. Which solute, when added to 1000 g of water, will produce a solution with the highest boiling point? 1) 29 g of NaCl 2) 58 g of NaCl 3) 31 g of C2H6O2 4) 62 g of C2H6O2 1 mole of NaCl → 2 moles of ions 1 mole of C2H6O2 → 1 mole of molecules

  14. Which solution will freeze at the lowest temperature? 1) 1 g of NaCl dissolved per 100 g of H2O 2) 1 g of NaCl dissolved per 1000 g of H2O • 1 g of C12H22O11 dissolved per 100 g of H2O 4) 1 g of C12H22O11 dissolved per 1000 g of H2O

  15. Which solution will freeze at the lowest temperature? 1) 1 g of NaCl dissolved per 100 g of H2O __1 g____ = 0.017 mol → 0.034 mol of ions 58.8 g/mol (NaCl) (Na+1 and Cl-1) 2) 1 g of C12H22O11 dissolved per 100 g of H2O __1 g___ = 0.0043 mol of molecules 232 g mol

  16. Effect of NonvolatileSolute • Boiling Point Elevation (↑) • Freezing Point Depression (↓) • The more particles, the bigger the effect!

  17. Applications of colligative properties Salting roads in the winter time Using salted ice to make ice cream

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