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Page 1
CHAPTER 11: PROPERTIES OF SOLUTIONS
SOLUBILITY
IONIC COMPOUNDS
Dissolving LiCl (s):
LiCl (s) → Li+ (g) + Cl– (g) DH = 853 kJ/mol
Li+ (g) + Cl– (g) + H2O (l) → Li+ (aq) + Cl– (aq) DH = –890. kJ/mol
LiCl (s) + H2O (l) → Li+ (aq) + Cl– (aq) DHsoln = –37 kJ/mol
Note: some soluble salts have an endothermic heat of solution, like KCl (DHsoln = +17.2 kJ/mol). CHEM 2 explains why KCl is soluble despite having a positive DHsoln.
NaCl (aq)
H O1 ItH o H Hlo i s St
Nat 1 Nat Ct HundH 08 H i fl y H lo H o
HH H
Waters Orientaround iions ox 8 toward Natand forms ion dipoleforces strong
breaksolidtakes E
breakwatersHbondstakesE ion dipole
forces releaseE
Page 2
MOLECULAR COMPOUNDS
Water + CH3CH2OH (Alcohol) Water + C5H12 (Pentane, like gasoline)
Like Dissolves Like Principle:
If solute and solvent are “like” each other in polarity, they dissolve.
If they are “unlike” each other, they don’t dissolve.
AQUEOUS SOLUBILITY (Ionic Compounds)
Salts are Soluble with: (1) Group IA metal ions; (2) Ammonium ions; (3) Nitrates, Nitrites, Chlorates, and Perchlorates; (4) Acetates (except with aluminum and silver); (5) Halogens (except with silver, lead(II), and copper(I) ions); (6) Sulfates (except with barium, calcium, strontium, and lead(II) ions). Salts are Insoluble with (applies only when situations 1-6 are absent): (7) Hydroxides (except with barium); (8) Carbonate, Chromate, Phosphate, and Sulfite ions; (9) Sulfide ions (except with Group IIA metals); (10) Other ions not previously mentioned.
CH3CH2OH (aq)
CH2O
HH3C
Often soluble salts have til 1 charges tweakionic bonds
Insoluble salts tend to have higher charges
sI 0
St StCHCHIH E H
1
Hbond H
Water orientsaround polar area
polar polar polar nonpolar
Page 3
Water Soluble
Glucose (C6H12O6)
a sugar
Alanine (C3H7NO2) an amino acid
Cadaverine (C5H14N2) smell of rotting flesh
Water Insoluble
Napthalene (C10H8) in moth balls
Cyclohexane (C6H12) a solvent
Dieldrin, (C12H8Cl6O) insecticide toxic to humans
Which of these should be soluble in water?
Hexachlorobenzene
probable human carcinogen, previously used fungicide on wheat
Furan possible human carcinogen,
small # in roasted coffee
Ascorbic acid Vitamin C
Vitamin E
CH
CHCH
CH
CHO
HO
OH
OH
OHCH2HO
CHCO
N
CH3
O
HH
HN
CH2CH2
CH2CH2
CH2N
H
H
H
H
C
CC
C
CC
CC
CC
H
H
H
H H
H
H
H
CH2
CH2CH2
CH2
CH2CH2
CH C CCCH C
C
CHCHCHCH
CH2
O
Cl ClCl
Cl Cl
Cl
C
CC
C
CC
Cl
Cl
ClCl
Cl
Cl C
C CC
OH
HH
HO
CH CC
C
O
OH
OHCH
CH2
HO
HO
C
CC
C
CC
OC
CH2CH2
CH3
O
H3C
CH3
CH2CH2CH2CHCH2CH2CH2CHCH2CH2CH2CH CH3
CH3CH3 CH3 CH3H
polar
og oooo o
polarareasH OH
St s TnotHbond
water soluble compounds have polar bonds often
many involving DX TN which can H bond w
water
Water insoluble are nonpolar have no OX or N
can't H bond or have a lot more nonpolarthan polar areas
00
too nonpolar
Ddissolves innonpolarCeltic
Page 4
GAS SOLUBILITY IN LIQUIDS
Henry’s law
C = kH·P
C = concentration of dissolved gas kH = Henry’s law constant for a solution P = partial pressure of gas solute above the solution
Sample Problem:
Calculate the concentration of CO2 (aq) in 25 ˚C water, when the atmosphere has a PCO2 of 4.0 × 10–4 atm. The Henry’s law constant for CO2 in water is 0.031 M/atm at 25 ˚C.
Water Solubility of Gases at 25 ˚C
Gas Water Soluble
g / 100 g water Gas Water
Soluble g / 100 g
water
H2 N 0.00016 CO2 0.169
O2 N 0.0043 SO2
11.28
N2 N 0.0019 NH3
What can you do to increase the concentration of dissolved CO2?
Sample Problem:
Calculate the solubility of CO2 (aq) at 25 ˚C, when bottled with a CO2 pressure of 5.0 atm over the liquid.
O C O
OSO
CO2 (aq) ??
y m x 6
Psas
C KH P O03h1m 4.0 104 ath lo.EEf nM
Npoke Y
polar52.9 H It
1dLRoz
5aAs RozP CozSolubilityIs
PanC KHP 0.0311hm 5 Oath 10.16mL
Page 5
Sample Problems:
At 1 atm, the partial pressure of N2 is 0.7809 atm (as 78.09% of air is N2). The solubility of N2 at 25 ˚C is 0.00055 M.
a. Calculate the Henry’s law constant for N2 at 25 ˚C.
b. At 3 atm, the PN2 = 3 × 0.7809 atm = 2.34 atm. Calculate the concentration of N2 (aq) at this pressure.
Scuba Diving and “The Bends”
GAS SOLUBILITY + TEMPERATURE
Gas solubility Pouring cold vs. warm soda Lake cooling of nuclear power plants
conc
C KH P KH f Ojai 10.000704ohm
0KHP 0.0007014 2.34 atm 10.0016M
Nz ag0.00055M
If ascend
p 3a too quickly
gases formGmagen9 6 in blood
Nz as6,0016M
As T T gas solubility f
Page 6
CONCENTRATION UNITS
DEFINITIONS
Concentration = !"#$%&%')*+,#--./#(..3.+)-"%.)-#/3./!"#$%&%'5/.+.$%(..3.%)%#-)
Molarity (M) Molality (m) Mass Percent (%) Mole Fraction (6)
M = ,)-.+(+)-"%.)7(+)-"%&)$) m =
,)-.+(+)-"%.)83(+)-9.$%) % =
,#++:%)%#-,#++ × 100 6A =
,)-.+:%)%#-,)-.+
Sample Problem:
Industrial strength hydrogen peroxide is 30.0% H2O2 by mass and has a density of 1.11 g/mL. Calculate the molarity, molality, and mole fraction of H2O2 in this aqueous solution.
a. Molarity
b. Molality
c. Mole fraction of H2O2
M molHz Mi Oj88m 19.79Mt
L solution
30.0
z i 0.88M30 Og HzOz 0.882 notHz0z
34.02 I z 1,01 t 2116.01009 solution fig uj 0.0901L solution
m not Hz0z 0.882 notk 7 0.0700kg
12.6 moykgorll2com
9100gsolution 3,1 5 70.0g water jook
molfyzaocation moth 0.882 mottotal moles
1 noy
88m01to.sgzT10.18527
70.0g water X o 0.185 like 18.5 118.02 g
211.011 t 16 oo Xwater 0.81581.5
Page 7
COLLIGATIVE PROPERTIES OF SOLUTIONS
Colligative Properties: only depend on the concentration of solute, not their identity.
VAPOR PRESSURE OF SOLUTIONS
All liquids / solutions at 20 ˚C:
Pwater = 17. 5 torr
Pwater = 16.6 torr
Pwater = 16.6 torr
Water 2.97 M sugar (aq) 2.97 M ethylene glycol (aq)
Raoult’s law
Psoln = 6solvent ·P˚solvent
Psoln = vapor pressure of the solution (meaning # of solvent in gas phase) 6solvent = mole fraction of solvent P˚solvent = vapor pressure of the pure solvent
Sample Problems:
Calculate the vapor pressure of a 2.97 M sugar solution (mole fraction = 0.0516 sugar) at 20.0 ˚C. The vapor pressure of water at 20.0 ˚C is 17.552 torr.
Which has the lowest vapor pressure?
Water 1.0 M sugar (aq)
(C12H22O11)3.0 M fructose (aq)
(C6H12O6)
Howmuchnot what
Non Volatile solutes lower the Vapor pressureof a solution
qpure
Psoin Xsoetposoh.at 0.9484 17.552 ton
watero.O
I
116.65171111Il