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Colligative Properties

This article explores how the addition of solutes affects the properties of water as a solvent, focusing on colligative properties like conductivity, boiling point elevation, and freezing point depression. It analyzes how pure water, which does not conduct electricity, contrasts with ionic solutions that do, and explains the significance of solute concentration on these properties. The article also discusses different types of solutes, including ionic and covalent, and how they influence the behavior of solutions, supported by examples such as NaCl and C6H12O6.

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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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