This document discusses solubility and how it is affected by various factors. It states that the enthalpy change of solution (ΔHsolution) determines whether a solution will form spontaneously. A polar solute in a polar solvent typically has a small positive or negative ΔHsolution and will form a solution. Nonpolar solutes in water have a large positive ΔHsolution and no solution forms. Temperature, pressure, and the "like dissolves like" principle can also impact solubility. Colligative properties depend on the number of particles in solution, whether from electrolyte dissociation or non-electrolyte molecules. vapor pressure is lowered and boiling point is elevated in solutions due to the presence of solute particles

1. ∆H1Solute pull apart solute particles
∆H2 Solvent – pull apart solvent molecules
∆H3 attraction of solute and solvent
∆G =∆H + T∆S ∆G = + for spontaneous processes
∆H1 ∆H2 ∆H3 ∆Hsolution outcome
Solute solvent Solute-solvent overall
Polar solute (EtOH) Large + Large + Large - Small (- or +) Soln forms
Polar solvent (water) (if ∆Hsolution
not too positive)
Nonpolar solute (oil) Small + Large + Small - Large + No solution
Polar solvent (water)
Non-polar solute (oil) Small + Small + Small - Small (+ or -) Solution forms
Non-polar solvent (gasoline) (~ideal)
Polar solute (EtOH) Large + Small + Small - Large + No solution
Non-polar solvent (oil) forms
Ionic solute (NaCl) Large + Large + Large - Small (+ or -) Solution forms if
Polar solvent (water) (can be ∆Hsolution not too
relatively large) positive
if ∆Hsolution + solution process is “entropy driven”

2. Like dissolves like
# 21 Which likely to be soluble in benzene
CCl4 or NaCl
Hexane or glycerol
Acetic acid or hexanoic acid
HCl or propyl chloride

3. Temp effect – gases
Gas + liquid solution + energy
Temp increase increases energy available
Favors “dis” solution
Thermal pollution – effect on fish

4. # 25 and 26
PbCl2 NaOH
∆H for dissociation to aqueous ions
Using data from Ch 8 or appendix
Will solubility increase with increasing temp?

5. Pressure effect on solubility
Henry’s law
Increased pressure increase gas solubility
C g = k Pg
Pg = partial pressure of the gas above liquid
k – constant – characteristic of particular gas/liquid system
Carbonated beverages
The bends –
Difference in solubility of gases (nitrogen or helium as carrier gas) with
increasing P
Decompressing after diving
Hyperbaric chambers for CO poisoning, wound healing etc (direct
solubility)
Practice # 29

6. Typical Henry’s law problem
He in water 3.8 X 10-4 M/atm @ 25 oC (k)
? M/mm Hg
pHe =293 mm Hg @ 25 oC, what is [ ] in M
C g = k Pg
HW: 27, 29 Ch 10

7. Colligative properties
Due to number of particles in solution
Be familiar with
Electrolytes (soluble salts, SA, SB)
Completely dissociate into ions
Non-electrolytes
Molecular compounds (no ions)
Polar molecular compounds are water soluble
Weak electrolytes
WA, WB – partially dissociate
Note worksheet

8. Colligative properties
Due to number of particles in solution
1 mole sugar per liter = ? mol/L particles?
1 mole NaCl per liter
1 mole aluminum sulfate per liter
1 mole acetic acid
Electrolytes/nonelectrolytes

9. Vapor pressure
Pressure of the vapor above a liquid or solution –
depends on temp and identity
Raoult’s law - mix with volatile solute
VPsoln = XsoluteVP solute + XsolventVPsolvent
evaporation

10. Ideal solution of 2 volatile solvents (liquids)
1. What is the VP of pure hexane ___
2. What is the VP of pure pentane ___
3. Which is more volatile?
4. If X = 0.5, what is VP due to pentane___ hexane ___total VP _____
Raoult’s Law VPT = XAVPA + XBVPB
Related exercise:
1 mol benzene (C6H6), Po = 75 torr
2 mol toluene (C7H8) Po = 22 torr
What is the mf of benzene in the
mixture?
What is the vp of the mixture?
What is the mf of benzene in the
vapor phase?
Data is for a given temp
since pentane is a liquid
at RT, this must be for a
higher T

11. VP lowering
Non-volatile solutes decrease vp
Independent of nature of solute
Dependent on number of particles in solution
Raoult’s law -- except solute does not exert vp (non-
volatile)
VPsolution = Xsolvent VPsolvent
VPlowering = Xsolute Vpsolvent
VPsolution + Vplowering = VPsolvent

12. VPsolution = Xsolvent VPsolvent
VPlowering = Xsolute VPsolvent
VPsolution + VPlowering = VPsolvent
Normally used with non-electrolytes
# 35
Note: mole fraction concentration unit used

13. Boiling point elevation
If solutes depress vp, to boil (vp = 760) temp must be
elevated
Depends on concentration of particles in solution and on
solvent
Use molality mol solute particles/kg solvent
BP elevation = k i m
k= bp constant for solvent
i= activity of solute (# particles/mol)
m = molality of solute (mol solute/kg solvent)
31,32 (bp’s)
Lab Wed benzoic acid in lauric acid

14. Freezing point depression
Solutes interfere with crystal formation
Salt added to ice – interferes with crystal structure,
ice structures breaks down – endothermic
process!!!!
Ocean water – ice bergs are fresh water --salt is not
included
1.86oC/mole of particles in 1 kg water
Melting ice
31, 32
General Chemistry Online: FAQ: Solutions: Why does
salt melt ice?

15. Review spec lab end of class
Assignments due
Make sugar solns
Spec lab:
Calc k
Calc energies
Calc unk conc
Emitted and abs colors
Resubmit
HW Ch 10 28-30 (Henry’s) 39 40 42-44 (fp, bp)