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CHEM 1A03: Intro. Chemistry I
Water & Aqueous Chemistry
Ch.5: Reactions in Aqueous Solutions
http://en.wikipedia.org/wiki/Thermite
http://visibleearth.nasa.gov/view_rec.php?id=2429
http://en.wikipedia.org/wiki/Iron_blast_furnace
http://www.chem1.com/CQ/
?http://www.scienceinafrica.co.za/2004/july/fluoride.htm
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Water: A Vital Natural Resource!
Significance of Water: Energy, Health & Environment“No single measure would do more to reduce disease and save lives
in the developing world than bringing safe water & adequate sanitation to all.”
UN Secretary-General Kofi Annan, 2003 International Year of Freshwater
“Water is probably the only natural resource to touch all aspects of human civilization —from agricultural and industrial development to
the cultural & religious values embedded in society.”
Koichiro Matsuura, Director-General, UNESCO
http://en.wikipedia.org/wiki/Waterfall http://en.wikipedia.org/wiki/Desert en.wikipedia.org/wiki/Hurricane
http://en.wikipedia.org/wiki/Drinking_water
en.wikipedia.org/wiki/Bottled_water
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Water: An Enigmatic Medium!
Unique Macroscopic Properties Essential to Life
1. Unusually high boiling point (b.p.) of liquid water at STP: bp = 100oC at 1 atm (Sea level) T,P-dependent
2. Density of ice (0.92 g/mL) < liquid water (1 g/mL) at 0oC:Ice expands with freezing: Lower packing density
3. High specific heat capacity of water (74 J/mol.K at STP): Absorbs thermal heat for storage/distribution/release
4. Water dissolves a variety of solutes as a solvent:Strong solvation properties for most polar molecules/ions
41 Anomalies of Water: http://www.lsbu.ac.uk/water/anmlies.html
http://visibleearth.nasa.gov/view_rec.php?id=2429
en.wikipedia.org/wiki/Iceberg
en.wikipedia.org/wiki/Snowflak
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iClicker Question #1iClicker Question #1Which intermolecular force accounts for water’s unusual high b.p.?
(a) Ion-dipole
(b) Dipole-dipole
(c) H-bonding
(d) Van der Waals
(e) none of the above
Hydrogen bonds: possible because
of water’s extreme polarity
OH H
Molecular Dipole
•• ••
Fig. 5-1a, p. 152 (143, 9th ed.)
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Solubilization of polar/ionic solutes: Hydration
Energetically favorable H2O-solute interactions:H-bonding (dipole-dipole) with solutes (O-H, N-H , C=O)+/- ion-dipole forces
Solute Solvation by Water
CH3CH2O-H
Dipole-dipole interactions
Na+-
+
+
-+
+ +
+
+
+
+
++
+
-
-
- -
Ion-dipole interactions
Cl--
+
+
-
+
++
+
+
+
+
++
-
-
-
Hydration shell
+-
..
..
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Properties of Water Vital for Molecular Behaviour
Protein Folding, Activity & Drug Binding
Human Serum Albumin (HSA)
Ion Hydration, Sodium Pumps & Ion Transport
Sodium Ion
Dichlorodiphenyl-trichloroethane (DDT)
Solubility, Toxicity & BioaccumulationCl Cl
ClCl
Cl
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Water auto-ionization: Water is amphoteric & conductive
Auto-ionization of Water
2H2O (l) H3O+ (aq) + OH- (aq)Kw Water acts as acid
& base with itself!
Kw = [H3O+][OH-]= 1 x 10-14 (25oC)
Purified De-ionized Water:
pH = -log[H3O+] = 7.0 Low conductivity since [H3O+] & [OH-] = 0.1 M
Electrolytes
Why isn’t [H2O] included in equilibrium expression?
H
H
O
H HO
H H
H ..O H
-+
O
H
OH H
Base
Acid Hydronium
Hydroxide
Transition State
..
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Solute Properties & Electrolytes
Non-electrolyte Strong electrolyte Weak electrolyte
Neutral molecule Fully charged ions Partially ionized molecule
Degree of ionization of an electrolyte in aqueous solution!
Fig. 5-3, p. 152-155 (143- 146, 9th ed.)
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Solutes as Electrolytes
1. Strong electrolyte (Ionic)Sodium Chloride:
3. Non-electrolyte (Neutral)Ethanol: Vodka (> 40% v) Spirit, Depressant &
Diuretic
2. Weak electrolyte (Weakly Ionic)Acetic Acid: Vinegar (5-8% w)
Preservative/Sour
Conductive ions
CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq)Ka = 4.8p
NaCl(aq) Na+(aq) + Cl(aq)
Intravenous supply of electrolytes
pKa = 16 No ionizationCH3CH2OH
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iClicker Question #2iClicker Question #2
(a) NaBr (aq, 1M)
(b) CH3OH (l)
(c) CH3COOH (aq, 1M)
(d) (NH4)2SO4 (aq, 1M)
(e) H2O (l)
Which of the following would be the strongest conductor of electricity?
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1. Solubility or Precipitation Reactions: (ion transfer)
2. Reduction-Oxidation (Redox) Reactions: (electron transfer)
3. Acid-Base Reactions: (proton transfer)
Major Types of Aqueous Chemical Reactions
Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s)
CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq)
K is a measure of extent of chemical reaction & transformation!
Cu(NO3)2(aq) + 2 NaOH(aq) Cu(OH)2(s) + 2 NaNO3(aq)
Lab 2
Lab 2
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Solubility: Qualitative Guidelines
Table 5-1; p. 156-159 (146-149, 9th ed.)
Soluble: Strong Electrolytes (Ksp >> 1)
Insoluble: Weak Electrolytes (Ksp << 1)
KI (aq) K+ (aq) + I- (aq)
CdCO3 (s) Cd2+ (aq) + CO32- (aq)
“slightly soluble” = soluble
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Net Ionic Reaction
Precipitation of AgI (s)
AgNO3 (aq) + KI (aq) AgI (s) + KNO3 (aq)
AgI (s)Ag+ (aq) + I- (aq)
Net Ionic Equation
or
AgI (s) + K+ (aq) + NO3- (aq)Ag+ (aq) + NO3
- (aq) + K+ (aq) + I- (aq)Spectator Ions
Derived from Strong Electrolytes
p. 157 (147, 9th ed.)
Total Ionic Equation
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Practice Exercise & Solution
Practice Question:
Determine the mass of KI needed to precipitate 0.1 mM of AgNO3 in a 20 mL sample solution.
Balanced equation:AgNO3 (aq) + KI (aq) AgI (s) + KNO3(aq)
Moles of AgNO3 present in solution:(1 x 10-4 moles/L) x (2 x 10-2 L) = 2 x 10-6 moles of AgNO3
moles of KI = moles of AgNO3, from the balanced reaction.
Mass of KI = 2 x 10-6 moles x 166.0 g/mol = 0.3 mg
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Solubility & Precipitation: Demo#1
Ksp = 8.3 x 10-17
Solubility Product (defined by Ksp)
PrecipitationK = 1/Ksp = 1.2 x 1016
AgI (s)Ksp
Ag+ (aq) + I- (aq)
AgI (s)1/Ksp
Ag+ (aq) + I- (aq)
AgNO3 (aq) NaI (aq) AgI (s) + NaNO3 (aq)Fig. 5-7 (5-4 9th ed.)
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Solubility & Precipitation: Demo#2
Fig. 18-1, pg 752
Ksp = 7.1 x 10-9PbI2 (s) Pb2+ (aq) + 2I- (aq)Ksp
iClicker Question #3
What would be the impact of dissolving PbI2 in a 1.0 M solution of Pb(NO3)2?
a.Increase the solubility
b.Decrease the solubility
c.No effect on equilibrium
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Measure of the intrinsic solubility of a salt in aqueous solution Also temp., pH, ionic strength dependent; Ksp in pure water
A low Ksp << 1 implies a sparingly soluble or highly insoluble salt
Which form of apatite is least soluble & most resistantto demineralization (tooth decay)?
Solubility Product for Salts: Ksp
Ca5(PO4)3OH (s)Ksp
5Ca2+ (aq) + 3PO43- (aq) + OH- (aq)
Hydroxylapatite
Fluorapatite
Ca5(PO4)3F (s)Ksp
5Ca2+ (aq) + 3PO43- (aq) + F- (aq)
Ksp = [Ca2+]5 [PO43-]3 [OH-] = 1.0 x 10-36
Ksp = [Ca2+]5 [PO43-]3 [F-] = 1.0 x 10-60
en.wikipedia.org/wiki/Human_tooth
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Differential Solubility of Salts
Ca5(PO4)3OH (s)Ksp
5Ca2+ (aq) + 3PO43- (aq) + OH- (aq)
Hydroxylapatite:
Ksp = [Ca2+]5 [PO43-]3 [OH-] = 1.0 x 10-36
Determine the Relative Decrease in Solubility of Fluorapatite vs. Hydroxylapatite
Let x = [OH-] formed upon dissolution
Ksp = (5x)5 (3x)3 (x) = 84375 x9
x = [Ksp/84375] 1/9 = 2.84 x 105 MMolar solubility of
hydroxylapatite
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Differential Solubility of Salts…contd
2.84 x 105 M = 4606.11 x 108 M
Similarly, for Fluorapatite:
Ksp = [Ca2+]5 [PO43]3 [F] = 1.0 x 1060
Ca5(PO4)3F (s)Ksp
5Ca2+ (aq) + 3PO43- (aq) + F- (aq)
Hydroxylapatite 460-fold more soluble than fluorapatite
x = [Ksp/84375] 1/9 = 6.11 x 108 M
Let x = [F] formed upon dissolution
Ksp = (5x)5 (3x)3 (x) = 84375 x9
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What is the molar solubility of cobalt (II) hydroxide (Ksp = 1.6 x 10-15)?
Co(OH)2 Co2+ + 2OH−
a. 6.1 x 10-6
b. 9.3 x 10-6 Ksp = [x][2x]2
c. 8.7 x 10-6 1.6 x 10-15 = 4x3
d. 7.4 x 10-6 x = 7.4 x 10-6
e. 1.1 x 10-6
Take Home ProblemTake Home Problem
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Application: Low Cost Defluoridation Method
Inexpensive, renewable and low cost method needed for defluoridation of drinking water in villages of developing countries
Ion-exchange process uses charred animal bone that is pulverized, filtered & washed for defluoridation via F- adsorption
Ca5(PO4)3OH (s) + F- (aq)Kex
Ca5(PO4)3F (s) + OH- (aq)Ion-exchange Mechanism
Regenerated with NaOH & H2O washRock/Pebble Layer
Charred Bone Layer
Charcoal/C
Fluoridated Water
Treated Water
Filtration Device
Water
Also effective for adsorbing
Pb, As, Hg
http://www.scienceinafrica.co.za/2004/july/fluoride.htm
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Q vs Ksp: Practice Question
Precipitation of PbS (s): Lead Contamination
Will a precipitate form if 0.50 mL of 10 M of K2S is mixed with 250 mL of 0.10 M Pb(NO3)2 ?
K2S (aq) + Pb(NO3)2 (aq) 2KNO3 (aq) + PbS (s)
Ksp = [Pb2+] [S2-] = 3.0 x 10-29
PbS (s) Pb2+ (aq) + S2- (aq)Ksp
Initial Concentration of K2S After Mixing Solutions:
Initial Concentration of Pb(NO3)2After Mixing Solutions:
= (1x10-5 mol/L*5x10-4 L) / 2.505x10-1 L
= 1.996 x 10-8 M
= (1x10-7 mol/L*2.50x10-1 L) / 2.505x10-1 L
= 9.980 x 10-8 M
Q = [Pb2+][S2-] = (9.98 x 10-8)(1.996 x 10-8) = 2.0 x 10-15 >> Ksp
Therefore, precipitate of PbS (s) will form!
www.cbc.ca/news/background/water/lead-pipes.htmlhttp://www.sxc.hu/photo/158242
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What is the value for Qsp if 0.500 mL of 1.50M BaCl2 is mixed with 0.600 mL of 0.20M NaOH?
a. 8.1 x 10-3
b. 7.7 x 10-3
c. 2.3 x 10-3
d. 9.1 x 10-2
e. 7.4 x 10-2
iClicker Questions #4 & #5iClicker Questions #4 & #5
If the Ksp for Ba(OH)2 is 5 x 10-3, will a precipitate form?
a.Yesb.No
24Ch 5-2, p. 159 (p. 149, 0th ed.)
Which of the following reactions will result in formation of a precipitate?
NaOH (aq) + MgCl2 (aq)
(NH4)2SO4 (aq) + ZnCl2 (aq)
BaS (aq) + CuSO4 (aq) CuS (s) + BaSO4 (s)
ZnSO4 (aq) + 2NH4Cl (aq)
Mg(OH)2 (s) + 2NaCl (aq)2
Note that precipitation reactions involve an ion-exchange process without changes in oxidation state of any species
(i)
(ii)
(iii)
(A) i (D) i and ii
(B) ii (E) ii and iii
(C) iii
Take Home ProblemTake Home Problem
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Reduction-Oxidation Reactions (Redox)
• A redox reaction can be identified by changes in oxidation numbers (O.N.) in the reactants and products
• The reducing agent loses electrons and is oxidized• The oxidizing agent gains electrons and is reduced
Example (Lab 2):
Zn(s) + 2 HCl(aq) → H2(g) + ZnCl2(aq)
Zn(s) is oxidized (loses 2 e)
H+(aq) is reduced (each H+ gains 1 e)
Zn is the reducing agent
H+ is the oxidizing agent
O.N. 0 +1 -1 0 +2 -1
LEO says GER or OIL RIG
p. 165-177 (153-163, 9th ed.)
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Concept Check: Oxidation States of Nitrogen
N Biogeochemical Cycle
Fig. 5-15, p. 176 (5-9, p 162, 9th ed.)
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iClicker Question #6iClicker Question #6
What is the oxidation number for phosphorous in Na2HPO4?
a. 0b. +3c. -2d. +5
28
Redox Reactions
Thermite Reaction (or Goldschmidt reaction, 1893) A classic redox reaction involving hematite (rust) and aluminum for welding applications/pyrotechnics
http://www.youtube.com/watch?v=Yex063_Fblk
°H < 0; T > 2,000 K
Fe2O3 (s) + 2Al (s) 2Fe (l) + Al2O3 (s)+3 00 +3
Oxidizing agent
Reducing agent
Highly Exothermic!Consider Half-Reactions
1. Fe3+ (s) + 3e- Fe (l) Reduction (Gains e)
2. Al (s) Al3+ (s) + 3e- Oxidation (Loses e)
A redox reaction is an electron transfer process!http://en.wikipedia.org/wiki/Thermite
29
iClicker Question #7iClicker Question #7
Identify the oxidizing agent in the following redox reaction:K2Cr2O7 (aq) + HI (aq) --> KI (aq) + CrI3 (aq) + I2 (s) + H2O (l)
a. Ib. Cr2O7
2-
c. K+
d. Cr3+
e. H2O
30
Steel and related iron-based alloys are widely used in construction
Smelting of iron ore in a blast furnace Chemical reduction method for iron (Fe) extraction; Feedstocks: C, Fe2O3, CaCO3
From the Iron Age to Post-Modern Age
Reduction of Iron Oxide
Fe2O3 (s) Fe (l)
+3 0+2 +4
0C (s) + ½ O2 (g)
H° < 0Purify /Alloy
Fe2O3 (s) + 3 CO (g) Fe (l) + 3 CO2 (g)
Steel & Steel AlloysSlag
Stainless steel
Fe (Cr, Ni)http://en.wikipedia.org/wiki/Iron_blast_furnace
http://en.wikipedia.org/wiki/Iron_ore
http://en.wikipedia.org/wiki/Stainless_steel
31
Hamilton: Steel CityBlast Furnace: Continuous Generation of Fe (l)
Hot Air Injection
C, Fe2O3, CaCO3
Pig Iron, Fe (l) 3 - 4 % C
Slag (Silicates)
Waste Gases: CO2, CO, SO2, NOx, H2O
Fig 23-9 p. 1044 (Fig 23.8, pg 976, 9th ed.)
Steel: Fe < 1% C
Scrubbing of waste gases needed to reduce emissions
& lower energy costs!
U. S. Steel Canada (Stelco) & ArcelorMittal Dofasco Inc.
32
Balancing Redox Reactions: Half-reactions
p 170-174 (p. 157-161, 9th ed.)
1. Deduce the oxidation numbers for all species This will identify the oxidizing and reducing agents
2. Write reduction and oxidation skeleton half-reactions3. Balance the redox atoms (usually not O, H unless they are participating in the redox chemistry) 4. Add the correct number of electrons to each half-reaction 5a. If acidic conditions: Balance O by adding H2O then H by H+
5b. If basic conditions: Balance as if in acidic conditions, then add OH- to balance the H+ (making water), then cancel the H2O (or balance the negative charges by adding OH-, then balance O & H by adding H2O)6. Check atoms and charges. Multiply half-reactions by a factor, if needed, to make the number of electrons transferred match. 7. Write the net redox reaction!
33
Balancing Redox Reactions: Acidic Conditions
Fe2+ (aq) + MnO4- (aq) Fe3+ (aq) + Mn2+ (aq)
Half-cell Reactions:
Fe2+ (aq) Fe3+ (aq) Oxidation + 1e-
Reduction MnO4- (aq) Mn2+ (aq)+ 5e- + 4H2O (l)
+7+ 8H+ (aq)
Net Balanced Redox Reaction
X 5
5Fe2+ (aq) + MnO4- (aq) + 8H+ (aq)
Balance the following reaction under acidic conditions:
5Fe3+ (aq) + Mn2+ (aq) + 4H2O (l)
p. 171-172 (157-158, 9th ed.)
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Balancing Redox Reactions: Basic Conditions
SO32 (aq) + MnO4
(aq) SO42 (aq) + MnO2 (s)
Half-cell Reactions:
SO32 (aq) + H2O (l) SO4
2 (aq) Oxidation + 2e
Reduction MnO4 (aq) MnO2 (s)+ 3e + 4H+ (aq)
+7
Net Balanced Redox Reaction
X 3
3SO32 (aq) + 2MnO4
(aq) + H2O (l)
+4 +6
+4X 2
+ 2H+ (aq)
+ 2H2O (l)
Balance the following reaction under basic conditions:
3SO42 (aq) + 2MnO2 (s) + 2OH (aq)
p. 172-174 (158-160, 9th ed.)
3SO32 (aq) + 2MnO4
(aq) + 2H+ (aq) 3SO4
2 (aq) + 2MnO2 (s) + H2O (l)
35
iClicker Question #8iClicker Question #8
When the following is balanced in a basic solution:MnO4
- (aq) + C2O42- (aq) --> MnO2(s) + CO3
2-
The coefficient in front of CO32- is:
a. 1b. 2c. 3d. 4e. 6
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Disproportionation Reactions
Hydrogen Peroxide (H2O2) Reactive molecule because of weak O-O single bond
One reactant (H2O2) acts as both reducing and oxidizing agent
OH
O
H.... ..
..
2H2O2 (aq) 2H2O (l) + O2 (g)
3% H2O2 as disinfectantH2O2 (aq) O2 (g) + 2e- + 2H+
H° < 0
Half-Reactions
Oxidation-1 0
Reduction H2O2 (aq) + 2e- + 2H+ 2H2O (l) -1 -2
Topical antiseptic as H2O2 can oxidize microbes
2H2O2 (aq) 2H2O (l) + O2 (g)
p. 174 (p. 160, 9th ed.)
37
Observe and predict the outcome of these two reactions
REDOX Chemical Reactions: Demo
Redox Chemical Reactions
CuSO4 (aq) + Zn (s)
AgNO3 (aq) + Cu (s)
1.
2.
Observations…
Cu (s) + Zn2+ (aq)
Ag (s) + Cu2+ (aq)
As in Lab 2
38
A Closer Look…
Cu (s) + Zn2+ (aq)CuSO4 (aq) + Zn (s)
Fig 5-12, p. 167 (Fig 5-7, p. 155)
39
Acid-Base Reactions
• Involve proton (H+) transfer (Bronsted-Lowry definition)
Example:
• The focus of an upcoming section (Ch 16)
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) (Lab 1)
Acid Base (OH)
H+ donor H+ acceptor
p. 160-165; 177-181 (p. 149-153, 163-165, 9th ed.)
