Colligative Properties

1. Colligative Properties

2. Can a solute change the properties of a solvent when added together to create a solution?

3. consider aqueous solutions • solvent = water How do properties of aqueous solution compare to properties of pure water?

4. Conductivity • pure water does not conduct electricity • some aqueous solutions do • to conduct electricity asolution must contain ions

5. conductivity depends on nature of the solute particles

6. molecular (covalent) solutes DO NOT conduct in any form • C6H12O6(s) • C6H12O6(aq)

7. ionic solutes DO conduct in aqueous and liquid forms but NOT in solid form • NaCl(s) • NaCl(l) √ • NaCl(aq) √

8. Colligative Properties • depend on number particles in solution NOTtype particles • doesn’t matter what kind of particles (ions or molecules) • concentration of particles doesmatter

9. What are some colligative properties? • vaporpressure (VP) • decreases (↓) • freezing point (fp) • decreases (↓) • boiling point (bp) • increases (↑) • change in Osmotic Pressure

10. higher the concentration of solute particles, the greater (larger) the effect on colligative properties

11. Does it matter if solute is ionic or covalent? YES • number of particles will vary • effected by concentration: • greater concen = greater effect • lower concen = lesser effect

12. ionic solutes • dissolve in H2O • dissociate into (+) & (-) ions [more particles/moles solute]

13. MgCl2(s) + H2O(l)  Mg2+(aq) + 2Cl(aq) 1 mole salt 3 moles ions (MgCl2) (Mg+2 & 2Cl-1) NaCl(s) + H2O(l)  Na+1(aq) + Cl-1(aq) 1 mole salt  2 moles ions (NaCl) (Na+1 & Cl-1)

14. Covalent solutes dissolve as molecules 1-to-1relationship betweenmoles solute & moles dissolved particles

15. Covalent substances C6H12O6(s)+ H2O(l)  C6H12O6(aq) 1 mole sugar → 1 mole dissolved molecules C6H12O6(s)C6H12O6(aq)

16. 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

17. 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

18. 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

19. 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 58g (1 mole) of NaCl → 2 moles of ions 62g (1 mole) of C2H6O2 → 1 mole of molecules

20. 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

21. 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

22. Effect of Non-volatileSolute on Colligative properties: • Boiling Point Elevation (↑) • Freezing Point Depression (↓) • the more particles, the bigger the effect! • the higher the bp and the lower the fp

23. Applications of colligative properties: 1. salting roads in the winter time ? NaCl or ? CaCl2 2. using salted ice to make ice cream - keeps ice cream from becoming like concrete