Lecture 48 Solutions I

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Lecture 48 - Solutions I
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Today...

• Types of solutions
• Concentrations
• Heats of solution
• Solubilities

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Solution Terminology

• Solvent - more plentiful
• Solute - dissolved in the solvent
• Miscible - soluble in each other in all
  proportions

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7 Types of Solutions

• 1. Gas dissolved in gas
• - air (O2, H2O, etc. in N2)
• - natural gas (butane, propane in methane)

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7 Types of Solutions

• 2. Gas dissolved in liquid
• - beer (carbonation)
• H2O(l) CO2(g) ? H2CO3(aq)
• - natural waters (dissolved O2)
• H2O(l) O2(g) ? O2(aq)

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7 Types of Solutions

• 3. Gas dissolved in solid
• - hydrogen in palladium

(interstitial H2)
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7 Types of Solutions

• 4. Liquid dissolved in liquid
• - beer (ethanol in water)
• C2H5OH(l) H2O(l) ? C2H5OH(aq)
• - antifreeze (ethylene glycol in water)
• - windshield washer (methanol in water)

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7 Types of Solutions

• 5. Liquid dissolved in solid
• - dental amalgam (Hg in Ag, Sn)

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7 Types of Solutions

• 6. Solid dissolved in liquid
• - beer (salts, flavorings in water)
• - sugar solution
• - ocean water (salts in water)

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7 Types of Solutions

• 7. Solid dissolved in solid
• - brass, steel, 10 karat Au

Cu (Sn)
Au (Ag)
Fe (C, Ni, Cr,)
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Concentration Units
g solute
mass
x 100
g solution
e.g. 100 g of 5 NaCl(aq) 5 g NaCl 95 g
H2O (96.7 mL !!)
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Concentration Units
temperature dependent
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Concentration Units
independent of T, V
e.g. HCl(aq) 2.0 m, r 1.033 g/mL.
Find M.
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Concentration Units

• 1. 2.0 m 2.0 mol HCl / kg solvent
• 2. 2.0 mol HCl 2 x 36.5 73.0 g HCl
• 3. Solution mass 73.0 1000.0 g
• 1073.0 g
• 4. solution volume 1073.0 g / 1.033 g/mL
• 1039 mL
• 5. M 2.0 mol / 1.039 L 1.92 M

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Concentration Units
g solute
mass
x 100
g solution
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Concentration Units
independent of T, V often used for gases, SFs
e.g. HCl 2.0 m Find XHCl
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Concentration Units
e.g. HCl 2.0 m Find XHCl

• 1. nHCl 2.0 mol
• 2. nH2O 1000 g / 18.0 g mol-1 55.5 mol

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Making Solutions
dissolution
Solution
crystallization
(solid)
phase separation
(liquid)
evolution
(gas)
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Making Solutions

• Solute Solvent ¾ Solution
• DH DHsoln
• DHsoln sum of 3 terms
• 1. DHsolute (separating the solute, gt0)
• 2. DHsolvent (separating the solvent, gt0)
• 3. DHmix (mixing the two, lt0)

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Heat of Solution
DHsolute
DHmix
Enthalpy
DHsolvent
DHsoln
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Heat of Solution

• DHsoln DHsolute DHsolvent DHmix

DHhydration
-DHlattice
(if solvent is H2O)
DHsoln - DHlattice DHhyd
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Heat of Hydration
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Heat of Hydration
M
i.e. small ions big force big
(negative)DHhyd
r
F µ 1/r2
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Heat of Hydration

• Ion Radius (pm) DHhyd
• Li 76 -510
• Na 102 -410
• K 138 -336
• Rb 152 -315
• Cs 167 -282

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Lattice Energy
smaller ions bigger force bigger
lattice energy
r
F µ 1/r2
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Heat of Solution

• DHsoln - DHlattice DHhyd
• e.g. NaCl DHsoln 3.9 kJ/mol
• (DHlattice DHhyd)
• e.g. NaOH DHsoln -44.5 kJ/mol
• (DHlattice ltlt DHhyd)
• e.g. NH4NO3 DHsoln 25.7 kJ/mol
• (DHlattice gtgt DHhyd)

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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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e.g. solubilities of alcohols

• Alcohol in H2O in C6H14
• (mol/100 g H2O) (mol/100 g C6H14)
• CH3OH ¼ 0.12
• CH3CH2OH ¼ ¼
• CH3(CH2)2OH ¼ ¼
• CH3 (CH2)3OH 0.11 ¼
• CH3 (CH2)4OH 0.030 ¼
• CH3 (CH2)5OH 0.006 ¼