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Concentration II
Factors Affecting ItChapter 12
Unit 10
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Solubility
Soluble / Insoluble:Ability of a solute to be dissolved in a solvent.
In reality, everything is slightly soluble.Atoms & molecules are so small (and there are so many of them), that a tiny amount will always dissolve even with insoluble substances.
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Solubility of Liquids
Miscible / Immiscible:For Liquids, describes ability to mix“Like Dissolves Like”Hydrophilic & hydrophobice.g. Oil and water are immiscible.Remember, ionic & compounds with hydrogen-bonding are hydrophilic.Must have the same polarity!
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Effects of T
Solubility generally increases with temperature.
Solubility of gases in liquids decreases with increasing temperature.
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Effects of P
Little effect on condensed phases (solids & liquids)
Great effect on solubility of gases. Henry’s Law: P = kHC The amount of gas that can be
dissolved is directly proportional to the pressure of the gas above the solution.
P1/C1 = P2/C2
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Henry’s Law in Action
Very little CO2 dissolves in 100 g H2O at 20 °C & normal pressures (PCO2~ 39 Pa)
A can of soda is pressurized with about 3 atm (300,000 Pa) of CO2.
0.45 g CO2 will dissolve in 100 g H2O at that pressure.
When you open a soda, the pressure drops and the CO2 comes bubbling out!
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Describing Concentration
Dilute: (adj) A solution containing a low amount of solute.
Dilute: (v) To decrease the concentration.
Concentrated: A solution containing a high amount of solute.
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Describing Concentration II
Unsaturated: A solution that can dissolve more of the solute.
Saturated: A solution that cannot dissolve any more of the solute.
A saturated solution will have some visible solute on the bottom of the container.
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Describing Concentration III
Supersaturated: A solution that holds more than the maximum amount of solute.
Most often by heating a solution to dissolve excess solute, then carefully cooling.
Must be extremely clean & still. Impurities & agitation can cause the excess
solute to fall out of solution (quickly).
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Dissociation
When ionic compounds dissolve in water, they dissociate into ions. Ions can conduct electricity. Called Electrolytes
Nonionic substances cannot dissociate. Do not conduct electricity Called Nonelectrolytes
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Making Solutions
Volumes are not additive! 50 mL H2O + 50 mL Ethanol ≠ 100 mL In order to make solutions:1. Add solute to small amount of solvent 2. Stir to dissolve.3. Add additional solvent until the total
volume reaches the desired level.
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T (°C)
g s
olu
te p
er
10
0 g
H2O
• Concentrations (g/100g H2O) under the line are considered unsaturated.
• Solutions with concentrations on the line are saturated.
• Solutions that have been carefully prepared to have concentrations above the line are supersaturated.