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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.)
27
iClicker Question #6iClicker Question #6
What is the oxidation number for phosphorous in Na2HPO4?
a. 0b. +3c. -2d. +5
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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
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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
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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
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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.
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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!
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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)
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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