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Transcript of Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Reactions Chapter 4.
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1
Reactions
Chapter 4
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Aqueous Solutions
Water is the dissolving medium, or solvent.
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Figure 4.1 The Water Molecule is Polar
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Some Properties of Water
Water is “bent” or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration occurs when salts dissolve in
water.
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• http://mathinscience.info/teach/k5_science/chemistry/mastering_matter/matter_animations/salt_cystl_watr_mol_web.swf
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Figure 4.2Polar Water Molecules Interact with the Positive and Negative Ions of a
Salt
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A Solute
dissolves in water (or other “solvent”)
changes phase (if different from the solvent)
is present in lesser amount (if the same phase as the solvent)
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A Solvent
retains its phase (if different from the solute)
is present in greater amount (if the same phase as the solute)
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Electrolytes
Strong - conduct current efficiently
NaCl, HNO3
Weak - conduct only a small current
vinegar, tap water
Non - no current flows
pure water, sugar solution
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Figure 4.5BaCI2 Dissolving
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Acids
Strong acids - dissociate completely to produce H+ in solution
hydrochloric and sulfuric acid
Weak acids - dissociate to a slight extent to give H+ in solution
acetic and formic acid
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Figure 4.6HCI (aq) is Completely Ionized
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Figure 4.8Acetic Acid in Water
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Bases
Strong bases - react completely with water to give OH ions.
sodium hydroxide
Weak bases - react only slightly with water to give OH ions.
ammonia
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Types of Double Displacement Reactions
Precipitation reactionsAgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
Acid-base reactionsNaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)
Oxidation-reduction reactionsFe2O3(s) + Al(s) Fe(l) + Al2O3(s)
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Simple Rules for Solubility
1. Most nitrate (NO3) salts are soluble.
2. Most alkali (group 1A) salts and NH4+ are soluble.
3. Most Cl, Br, and I salts are soluble (NOT Ag+, Pb2+, Hg22+)
4. Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4)
5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble)
6. Most S2, CO32, CrO4
2, PO43 salts are only slightly soluble.
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Describing Reactions in Solution
1. Molecular equation (reactants and products as compounds)
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
2. Complete ionic equation (all strong electrolytes shown as ions)
Ag+(aq) + NO3(aq) + Na+(aq) + Cl(aq)
AgCl(s) + Na+(aq) + NO3(aq)
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Describing Reactions in Solution (continued)
3. Net ionic equation (show only components that actually react)
Ag+(aq) + Cl(aq) AgCl(s)
Na+ and NO3 are spectator ions.
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Quick Review – Are you Ready?
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47%
53% 1. Yes
2. No
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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When Fe(NO3)2 dissolves in water, what particles are present in the solution?
0%
6%
88%
6% 1. Fe+ and (NO3)2–
2. Fe2+ and 2 NO3–
3. Fe and 2 NO3
4. Fe and N2 and 3 O2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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Pb(NO3)2 + 2 KI PbI2 + 2 KNO3
What is the observable evidence that the above reaction occurs?
88%
0%
0%
12% 1. An explosion.
2. A gas forms.
3. The solution boils.
4. A solid forms.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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When an acid and a base react to form a salt and water, the reaction is called a(n):
0%
100%
0%
0% 1. cancellation.
2. elimination.
3. neutralization.
4. adduct formation.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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Which mixture will produce a precipitate?
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1. NH3 + HF
2. HClO4 + KOH
3. Na2SO4 + PbCl24. Ca(NO3)2 + KC2H3O2
5. (NH4)2CO3 + Na3PO4
12%
24%
47%
18% 0%
1. 2 3 4 5
1. 1.
2. 2
3. 3
4. 4
5. 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is(are) the spectator ion(s) in the following reaction?
KOH (aq) + HF (aq) KF (aq) + H2O (l)
0%
6%
82%
6%
6% 1. K+
2. F–
3. K+ and F–
4. OH– and H+
5. OH–
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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Which of the following reactions has the net ionic equation:
H+ (aq) + OH– (aq) H2O (l)
1) HClO4 + KOH
2) HF + NaOH
3) H3PO4 + KOH
4) H2SO4 + Ca(OH)2
53%
0%
0%
41%
6% 1. Reaction 1
2. Reactions 1, 4
3. Reactions 2, 3
4. Reactions 2, 4
5. Reactions 3, 4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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Other Reactions
• Single displacement
• Combustion
• Synthesis
• Decomposition
All of these involve a transfer of electrons and are oxidation-reduction (Redox) reactions
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© 2009, Prentice-Hall, Inc.
Oxidation-Reduction Reactions
• An oxidation occurs when an atom or ion loses electrons.
• A reduction occurs when an atom or ion gains electrons.
• One cannot occur without the other.
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Rules for Assigning Oxidation States
1. Oxidation state of an atom in an element = 0
2. Oxidation state of monatomic ion = charge
3. Oxygen = 2 in covalent compounds (except in peroxides where it = 1)
4. H = +1 when bonded to nonmetal; -1 when bonded to metal
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5. Fluorine = 1 in compoundsThe other halogens have an oxidation number of −1
when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions (polyatomic ions with oxygen)
6. Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion
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Redox Reactions - Terms
• Oxidation – loss of electrons (increase in oxidation number)
• Reduction – gain of electrons (decrease in oxidation number)
• Oxidizing agent – the compound that is the electron acceptor
• Reducing agent – the compound that is the electron donor
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When an atom undergoes reduction, it _______ electrons.
0%
0%
6%
94% 1. gains
2. loses
3. retains
4. balances
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of sulfur in the following compound?
SO2
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6%
0%
94%
0% 1. -4
2. +4
3. -2
4. +2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of oxygen in the following compound?
MgO
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12%
88%
0%
0% 1. -4
2. +4
3. -2
4. +2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of Manganese in the following compound?
MnO2
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6%
0%
94%
0% 1. -4
2. +4
3. -2
4. +2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of Fluorine in the following compound?
F2
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18%
41%
6%
35% 1. -1
2. +1
3. 0
4. -2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of Sulfur in the following compound?
SO42-
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6%
6%
82%
6% 1. +8
2. +6
3. -2
4. +4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of manganese in the permanganate ion?
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59%
0%
29%
12% 1. +8
2. +6
3. -6
4. +7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is the oxidation number of nitrogen in the nitrite ion?
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24%
0%
12%
65% 1. +3
2. +5
3. -5
4. +2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is reduced in the following equation?
Al + Cu(NO3)2 Cu + Al(NO3)3
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0%
0%
89%
11% 1. Al
2. Cu
3. Cu(NO3)2
4. Al(NO3)3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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What is oxidized in the following equation?
Al + Cu(NO3)2 Cu + Al(NO3)3
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25%
25%
25%
25% 1. Al
2. Cu
3. Cu(NO3)2
4. Al(NO3)3
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What is reducing agent in the following equation?
Al + Cu(NO3)2 Cu + Al(NO3)3
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25%
25%
25%
25% 1. Al
2. Cu
3. Cu(NO3)2
4. Al(NO3)3
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What is oxidizing agent in the following equation?
Al + Cu(NO3)2 Cu + Al(NO3)3
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25%
25%
25%
25% 1. Al
2. Cu
3. Cu(NO3)2
4. Al(NO3)3
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Which substance is serving as the reducing agent in the following reaction?
14H+ + Cr2O72- + 3Ni 3Ni2+ + 2Cr3+ + 7H2O
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20%
20%
20%
20%
20% A. H2O
B. H+
C. Ni2+
D. Ni
E. Cr2O72-
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Balancing by Half-Reaction Method
1. Write separate reduction, oxidation reactions.
2. For each half-reaction:
Balance elements (except H, O)
Balance O using H2O
Balance H using H+
Balance charge using electrons
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Balancing by Half-Reaction Method (continued)
3. If necessary, multiply by integer to equalize electron count.
4. Add half-reactions.
5. Check that elements and charges are balanced.
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Half-Reaction Method - Balancing in Base
1. Balance as in acid.
2. Add OH that equals H+ ions (both sides!)
3. Form water by combining H+, OH.
4. Check elements and charges for balance.