Lecture 49 Solutions II

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Lecture 49 - Solutions II
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Review

• Types of solutions
• Concentration Units
• Heats of Solution

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Today...

• Solubilities vs structure
• Solubilities vs temperature
• Supersaturation
• Gases dissolved in liquids

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Solubility
solute
saturated solution
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solute solubility
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Solubility

• rule of thumb
• Like Dissolves Like
• (similar intermolecular forces)

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Solubility and Structure

• e.g. vitamins
• Fat Soluble Water soluble
• A, D, E, K B, C

anti-aging anti-cancer
anti-colds anti-scurvy
important in vision
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Solubility and Structure
Vitamin C
hydrophilic
easily excreted, must be consumed regularly
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Solubility and Structure
O-H
Vitamin A
hydrophobic
hydrophilic
fat soluble - stored by body
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Solubility and Structure

• Sucrose is C12H14O3(OH)8
• easily metabolized ? food energy
• Can convert it to C12H14O3(OR)8

large C-containing groups
not easily metabolized ? no calories
Olestra
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Solubility and Structure

• Olestra fake fat
• - hydrophobic ? good solvent for vitamins A, D,
  E, K

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Solubility and Structure
H
H
H
H
Biphenyl C12H10
H
H
H
H
H
H
Cl2
polychlorinated biphenyls (PCBs),
C12HxCl10-x
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Solubility and Structure
PCBs deposit in oceans
PCBs evaporate
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Biomagnification
polar bears (and people) eat seals,PCBs
Accumulate even more
high ppm
Seals (and people) eat fish, PCBs accumulate in
fatty tissues
ppb - ppm
Fish eat sediments, PCBs dissolve in fat
ppt - ppb
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Solubility and Temperature

• e.g. dissolution of NaCl(s)
• DHsoln 3.9 kJ/mol
• NaCl(s) H2O(l) 3.9 kJ ¾ Na(aq) Cl-(aq)

i.e. raise T ? equilibrium moves
right (solubility increases)
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Solubility and Temperature
NaCl
Solubility
NaOH
gases
T
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Supersaturation
solubility line
Supersaturation!
Concentration
expect crystallization!
T
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Supersaturation
supersaturated
saturated
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Supersaturation

• glucose in honey
• sucrose in jellies
• KHC4H4O6, (potassium hydrogen tartrate) in wine

chill, seed, filter (cold stabilization)
chill bottle
crystallization
no crystallization
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Solubilities of Gases in Liquids

• USUALLY, solubility µ 1/T

1.5
Fish OK
mg O2
Fish not OK
100 g H2O
0
0
100
T, oC
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e.g. Waste Heat Kills Fish

• (nuclear generating) stations
• waste heat
• warmer water
• lower O2 solubility

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warmer, less dense, less O2
cooler
Fish swim deeper looking for more O2
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e.g. Boiler Scale

• CO2(g) H2O(l) CO3-2(aq) ¾ 2 HCO3-(aq)

higher T, CO2 is less soluble
thus, more CO3-2(aq)
then, Ca2(aq) CO3-2(aq) ? CaCO3(s)
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Solubility and Pressure
Gas, pressurep
Gas(aq), saturated i.e. Gas(aq) solubility
H2O(l)
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Solubility and Pressure
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NO
solubility, mg gas/ 100 mL H2O
O2
H2
0
0
10
p, atm
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Solubility and Pressure

• solubility KH p (Henrys Law)

different for each gas
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Solubility and Pressure
e.g. beer (and other carbonated drinks)
pCO2 2.5 atm
KH,CO2 0.032 mol L-1 atm-1
How much CO2 is there in a bottle of beer?
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Solubility and Pressure

• solubility KH p
• 0.032 mol L-1 atm-1 2.5 atm
• 0.076 mol L-1
• x 0.341 L 0.026 mol CO2
• 1.1 g CO2

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e.g. The Bends
Lower Pressure, N2(g) less soluble in blood
High Pressure, N2(g) soluble in blood
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e.g. The Bends

• upon ascent, pressure decreases, and
• N2(aq) ? N2(g)

i.e. bubbles in blood!
prevent by using He instead of N2