CHAPTER 11: PROPERTIES OF SOLUTIONS...

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

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

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

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

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

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

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

CHAPTER 11: PROPERTIES OF SOLUTIONS...

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