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 a solution must contain ions

5. Conductivity depends on nature of the solute particles
molecular (covalent) solutes DO NOT conduct in any form
C6H12O6(s)
C6H12O6(aq)
ionic solutes DO conduct in aqueous and liquid forms but NOT in solid form
NaCl(s)
NaCl(l) √
NaCl(aq) √

6. Colligative Properties
Depend on number particles in solution not type particles
doesn’t matter what kind of particles (ions or molecules)
Concentration of particles does matter

7. What are some colligative properties?
Vapor Pressure
decreases (↓)
Freezing Point
Boiling Point
increases (↑)
change in Osmotic Pressure

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

9. 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

10. Ionic solutes dissolve in H2O dissociate into (+) & (-) ions
[ more particles/mole of solute]

11. 1 mole salt 3 moles ions NaCl(s) + H2O(l)  Na+1(aq) + Cl-1(aq)
MgCl2(s) + H2O(l)  Mg2+(aq) + 2Cl(aq)
1 mole salt 3 moles ions
NaCl(s) + H2O(l)  Na+1(aq) + Cl-1(aq)
1 mole salt  2 moles ions

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

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

14. 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

15. - do you want greatest or least change?
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:

16. 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) g of solvent
Answer: 1

17. 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

18. 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

19. Which solution will freeze at the lowest temperature?
1) 1 g of NaCl dissolved per 100 g of H2O
__1 g____ = mol → 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___ = mol of molecules
232 g mol

20. Effect of Non-volatile Solute on Colligative properties
Boiling Point Elevation (↑)
Freezing Point Depression (↓)
the more particles, the bigger the effect!

21. Applications of colligative properties
Salting roads in the winter time
? NaCl or ? MgCl2
Using salted ice to make ice cream
keeps ice cream from becoming like concrete