Factors Affecting
Solubility
• at high P, more molecules of gas are close to the
solvent
• more gas molecules strike surface and enter
solution.
• higher pressure = greater solubility
Factors Affecting
Solubility
Pressure Effects
• Soda is bottled with a PCO2 = 4-10 atm.
• As the bottle is opened, the partial pressure of CO2
decreases and solubility of CO2 decreases.
• bubbles of CO2 escape from solution.
Factors Affecting
Solubility
Temperature Effects
• Does sugar dissolve better in warm water than cold?
• As temperature increases, solubility of solids
generally increases.
• Sometimes, solubility decreases as temperature
increases (e.g. Ce2(SO4)3).
Factors Affecting
Solubility
Temperature Effects
• soda goes flat as it gets warm.
• gases get less soluble as T increases.
• Thermal pollution:
warm lakes = less CO2 and O2 for plants + animals.
Warm water = no O2 = DEAD FISH
Expressing Concentration
ppm of component =
Molal
Molality and Molar
Molarity
mass of component in solution
× 106
total mass of solution
• molality = moles solute/kg solvent ‘m’
• Stays constant with T changes
• Parts per million (ppm) =
1 mg of solute per kg of solution.
• Similar to Molarity for dilute, aqueous solutions
– In water,
then 1 ppm = 1 mg solute per liter of solution.
• What is molality when dissolving 25.0 g of calcium
chloride in 250 mL of water?
• Parts per billion (ppb) = 1 µg/L.
•1 credit card = 7.1 in2
•1 NFL field = 8.3x106 in2
•Calculate area of card in ppm
•0.86 ppm
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Colligative Properties
Mole Fraction
Lowering Vapor Pressure
• Mole fraction =
moles component
total moles all components of solution
What is mole fraction when dissolving 25.0 g of
calcium chloride in 250 mL of water?
• Colligative properties depend on quantity of solute
molecules, not chemical nature of solute.
•As liquid boils, randomness increases
•Solutes in solution increase randomness
•Vapor pressure (boiling point)
•Freezing point
•Osmotic pressure
•Non-volatile solutes reduce # of solvent
molecules that vaporize
PE can decrease when Energy spread out in more places
•vapor pressure is lowered.
•depends only on # of particles of solute.
Chemical randomness is called entropy
entropy includes randomness of particles and energy
• ∆Tb = Kbm
(temp change = constant x molality)
Colligative Properties
Lowering Vapor Pressure
• Table 13.4
•Same amount of entropy in each flask!
Colligative Properties
Boiling Point
• solution has a lower vapor pressure
than the pure liquid
Salt in water
•0% wt/wt =
•5% wt/wt =
•10% wt/wt =
BP
100 ºC
101 ºC
102 ºC
• A higher Temp required to increase vapor pressure
to 1 atm (normal B.P.) for a solution
• ∆Tf = Kfm
(temp change = constant x molality)
2
What is the boiling point of aqueous 0.032 m glucose
(C6H12O6) solution?
What is the freezing point of an aqueous 5.8 m NaCl solution?
∆Tf = Kxm (temp change = constant x molality of particles)
Osmosis
• Semi-permeable membrane: permits passage of
some components of a solution.
•
• Example: cell membranes, Gore-Tex
Solvent ??
•As solvent moves
across the
membrane, the fluid
levels in the arms
becomes uneven.
• Osmosis: movement of solvent from low solute
conc. to high solute conc.
Osmosis
• the pressure difference between the arms stops
osmosis.
Colligative Properties
Osmosis
• Hypotonic solutions: fewer ions than “normal”
• hypertonic solutions: more ions
• cells have semi-permeable membranes.
Colligative Properties
Colligative Properties
Osmosis
Osmosis
• Hemolysis:
–
–
–
–
red blood cells placed in a hypotonic solution;
higher solute concentration in the cell;
water moves into the cell.
The cell bursts.
• To prevent crenation or hemolysis, IV (intravenous)
solutions must be isotonic.
Osmosis
Colligative Properties
Osmosis
• Crenation:
– red blood cells placed in hypertonic solution (relative to
intracellular solution);
– cell has lower solute concentration inside than out;
– osmosis occurs, water passes through the membrane out
of the cell.
– The cell shrivels up.
Colligative Properties
Osmosis
– Cucumber placed in NaCl : pickle.
– Limp carrot placed in water becomes firm.
– Salty food causes retention of water and swelling of
tissues (edema).
– Water moves into plants through osmosis.
– Salt added to meat or sugar to fruit prevents bacterial
infection (bacteria lose water through osmosis and die).
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•Soaps and detergents
a 40 year old tree makes 40 liters sap
in 4 weeks, = 1 liter of syrup
•Micelle: 3-D structure of soap ions in water
•Soaps are salts of carboxylic acids -- carboxylates
•Detergents are sulfate or sulfonate salts
•Soaps ppt with Ca2+, detergents don’t
4
•Soap interacting with oil in water
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