1. Solutions
Part 2

2. Molality 2nd unit of concentration – Molality
(Molarity was the 1st unit of concentration)
While molarity; M= n/V
Molality is m = n/kg

3. Molality Molality is the moles of solute per kilogram of solvent.
*Solute – gets dissolved; solvent does the dissolving
Molality = mol of solute unit m = mol
kg of solvent kg

4. Molality
Ex. 1) What is the molality of a sol’n composed of 255 g of acetone, (CH3)2CO, dissolved in 200.g of water? Ex. 2) How many grams of silver nitrate are needed to prepare a m sol’n in mL of water? Assume: 1 mL H2O = 1 g H2O

5. Phase diagram show the phase of matter at a variety of P and T.
show the phase of matter at a variety of P and T.
Substances can be almost any phase, given the right P and T.
the triple point is where the solid, liquid, and gas phase of a substance coexist at equilibrium

6. Phase Diagrams

7. Phase Diagrams
Normal boiling point and normal melting point occur at 1 atm of pressure

8. H2O vs. CO2

9. H2O vs. CO2
H2O is less dense in the solid state (ice has lots of space in it), Notice that water has a negative slope between the solid & liquid on the phase diagram. Water is densest at 4oC.
Density of H2O(ℓ) = 1.00 g/mL
Density of H2O(s) = g/mL
CO2 goes straight from a solid to a gas at atmospheric pressure.

10. Colligative properties
Colligative properties are characteristics of a sol’n that are dependent upon the concentration of the solute. Ex. color intensity of Kool-aid

11. Types of Colligative Properties
1. boiling point elevation – the boiling point of a sol’n is always higher than the pure solvent. Why? boiling is harder to do b/c in normal boiling, you separate solvent mlcls from each other, but when boiling a sol’n you have to separate solvent mlcls from each other and also from the solute mlcls.

12. Types of Colligative Properties
2. freezing point depression – the freezing point is always lower than the pure solvent. Why? Freezing is harder b/c while freezing the solvent mlcls set up into a solid crystal, but in a sol’n the solute mlcls get in the way, making it more difficult to freeze. (lower fp)

13. Practical applications:
Cooking – NaCl in H2O, raises the bp so when H2O is boiling, food cooks faster.
Salting icy roads, lowers fp so it easier for the ice to melt off the roads.
Homemade ice cream!

14. Types of Colligative Properties
3. Vapor Pressure – sol’ns have different Pvap than pure solvents. The more conc. the sol’n, the lower the pressure. Why? It’s harder for the liquid solvent to turn into a gas when there are solutes in the way

15. Phase diagram of a solution
the triple point of a solution on a phase diagram moves down on the equilibrium line.
Solutions stay in the liquid form longer than pure solvents

16. Equations for B.P. Elevation/F.P. depression
ΔTb= kbim ΔTf= kfim
ΔT = change in boiling/ freezing pt.
m = molality of sol’n
k = constant
kb = oC/m
kf = 1.86 oC/m (for easier math, make it oC/m)
i = van’t Hoff factor (# of dissolved particles):
for molecular compounds (covalent compounds) i = 1
for ionic compounds count the # of different ions

17. Solving for i (van’t Hoff factor)
3. Find the van’t Hoff factor for each of the following:
a) Lithium carbonate
b) Disilicon tetrahydride
c) Carbon dioxide
d) Chromium (VI) chloride
e) Xenon heptafluoride
f) Magnesium sulfate

18. Ex. 4) What is the new freezing point of 17. 1g C12H22O11 in 200
Ex. 4) What is the new freezing point of 17.1g C12H22O11 in 200.g H2O Ex. 5) 1.00 kg H2O is used to dissolve 62.5g of Barium Nitrate. What is the new boiling point?