Kinds of Solutions
C h a p t e r 11
Solutions and Their Properties
Solute and solvent
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Kind of Solution
Example
Gas in gas
Air (O2, N2, Ar …)
Gas in liquid
Carbonated water
Gas in solid
H2 in palladium metal
Liquid in liquid
Gasoline (mixture)
Liquid in solid
Dental amalgam
(mercury in silver)
Solid in liquid
Seawater (NaCl)
Solid in solid
Metal alloys
Will a solution form?
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03
For Gas or solid dissolved in liquid:
SOLUTE - dissolved substance
SOLVENT - liquid
Liquids-liquids (minor component is solute)
“LIKE DISSOLVES LIKE”
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NaCl in water
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Free-energy Change
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-∆G ⇒ spontaneous ⇒ substance dissolves
+∆G ⇒ nonspontaneous ⇒ substance does not dissolve
∆G = ∆H - T ∆S
∆Hsoln and ∆Ssoln
Entropy of Solution (∆Ssoln)
∆Ssoln usually positive
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Enthalpy of Solution (∆Hsoln)
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Solvent - Solvent: Energy is required (+ ∆H) to overcome
forces between solvent molecules
Solute - Solute: Energy is required (+ ∆H) to overcome
intermolecular forces holding solute particles together
Solvent - Solute: Energy is released (- ∆H) when solute
particles are solvated (surrounded by solvent) ⇒greater
for small cations ⇒ increases with charge
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Enthalpy of Solution (∆Hsoln)
•
Exothermic ∆Hsoln:
•
Favorable process
•
Hot packs - CaCl2(s)
Examples
1.
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Enthalpy of Solution (∆Hsoln)
•
Endothermic ∆Hsoln:
•
Unfavorable process
•
Cold packs - NH4NO3(s)
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Predict the relative solubilities in the following cases:
Concentration Units
•
(b) KCl in carbon tetrachloride and in liquid ammonia,
1.
(c) urea (NH2)2CO in carbon disulfide and in water.
2.
3.
Is iodine (I2) more soluble in water or in carbon
disulfide (CS2)?
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Concentration: The amount of solute present in a given amount
of solution.
(a) Br2 in benzene (C6H6) and in water,
2.
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4.
Molarity (M)
Molality (m)
Mole fraction (X)
Mass Percent
3
Concentration Units - important!
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•
Molarity (M):
Molarity =
Moles of solute
Liters of SOLUTION
•
Molality (m):
Molality =
Moles of solute
Kilograms of SOLVENT
•
Mole Fraction (X):
Concentration Units
•
mass of solute
× 100%
mass of solution
mass of solution =mass of solute +mass of solvent
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•
Parts per Million:
•
Parts per million (ppm) = Mass of component x 106
Example
•
Total mass of solution
Percent by Mass (weight percent): The ratio of
the mass of a solute to the mass of a solution,
multiplied by 100%.
% bymassof solute =
Moles of A
XA =
Total number of moles
Concentration Units
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16
A sample of 0.892 g of potassium chloride (KCl) is
dissolved in 54.6 g of water. What is the percent by
mass of KCl in this solution?
= % mass x 104
•
One ppm gives 1 gram of solute per 1,000,000 g or
one mg per kg of solution. For dilute aqueous
solutions this is about 1 mg per liter of solution.
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Example
17
An aqueous solution is 5.50% H2SO4. How many
Example
•
moles of sulfuric acid (MM = 98.08 g/mol) are
dissolved in 250.0 g of the solution?
Example
•
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Molality from Mass: Calculate the molality of a
sulfuric acid solution containing 24.4 g of sulfuric
acid in 198 g of water. The molar mass of sulfuric
acid is 98.08 g.
Solution Formation
Molality from Molarity: Calculate the molality of a
5.86 M ethanol (C2H5OH) solution whose density is
0.927 g/ml.
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Solute + solvent ⇔ Solution
•
Saturated - equilibrium (equal number of ions going into
solution as returning from solution to the crystals)
•
Supersaturated - greater than equilibrium amount of solute
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Solution Formation
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•
Solubility: A measure of how much solute will dissolve in a
solvent at a specific temperature (saturated solution)
•
Miscible: Two (or more) liquids that are completely soluble
in each other in all proportions.
•
Solvation: The process in which an ion or a molecule is
surrounded by solvent molecules arranged in a specific
manner.
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