Transcript Chapter 4

Reactions in Aqueous Solution
Chapter 4
For test 3:
Sections 3.7 and 4.1 to 4.5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A solution is a homogenous mixture of 2 or more
substances
The solute is(are) the substance(s) present in the
smaller amount(s)
The solvent is the substance present in the larger
amount
Solution
Solvent
Solute
Soft drink(l)
H2O
Sugar, CO2
Air(g)
N2
O2, Ar, CH4
Soft Solder(s)
Pb
Sn
aqueous solutions
of KMnO4
2
An electrolyte is a substance that, when dissolved in
water, results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved,
results in a solution that does not conduct electricity.
nonelectrolyte
weak electrolyte
strong electrolyte
3
Conduct electricity in solution?
Cations (+) and Anions (-)
Strong Electrolyte – 100% dissociation
NaCl(s)
H 2O
Na+(aq) + Cl-(aq)
Weak Electrolyte – not completely dissociated
CH3COOH
CH3COO-(aq) + H+(aq)
4
Ionization of acetic acid
CH3COOH
CH3COO-(aq) + H+(aq)
A reversible reaction. The reaction can
occur in both directions.
Acetic acid is a weak electrolyte because its
ionization in water is incomplete.
5
Hydration is the process in which an ion is surrounded
by water molecules arranged in a specific manner.
d-
d+
H2O
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Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C6H12O6(s)
H 2O
C6H12O6(aq)
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A process in which one or more substances is changed into one
or more new substances is a chemical reaction
A chemical equation uses chemical symbols to show what
happens during a chemical reaction
reactants
products
3 ways of representing the reaction of H2 with O2 to form H2O
From Chapter 3 section 3.7
8
How to “Read” Chemical Equations
2 Mg + O2
2 MgO
2 atoms Mg + 1 molecule O2 makes 2 formula units MgO
2 moles Mg + 1 mole O2 makes 2 moles MgO
48.6 grams Mg + 32.0 grams O2 makes 80.6 g MgO
NOT
2 grams Mg + 1 gram O2 makes 2 g MgO
From Chapter 3 section 3.7
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Balancing Chemical Equations
1. Write the correct formula(s) for the reactants on
the left side and the correct formula(s) for the
product(s) on the right side of the equation.
Ethane reacts with oxygen to form carbon dioxide and water
C2H6 + O2
CO2 + H2O
2. Change the numbers in front of the formulas
(coefficients) to make the number of atoms of
each element the same on both sides of the
equation. Do not change the subscripts.
2C2H6
NOT
C4H12
From Chapter 3 section 3.7
10
Balancing Chemical Equations
3. Start by balancing those elements that appear in
only one reactant and one product.
C2H6 + O2
2 carbon
on left
C2H6 + O2
6 hydrogen
on left
C2H6 + O2
CO2 + H2O
start with C or H but not O
1 carbon
on right
multiply CO2 by 2
2CO2 + H2O
2 hydrogen
on right
2CO2 + 3H2O
multiply H2O by 3
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From Chapter 3 section 3.7
Balancing Chemical Equations
4. Balance those elements that appear in two or
more reactants or products.
C2H6 + O2
2 oxygen
on left
2CO2 + 3H2O
multiply O2 by 7
2
4 oxygen + 3 oxygen = 7 oxygen
(3x1)
on right
(2x2)
C2H6 + 7 O2
2
2CO2 + 3H2O
2C2H6 + 7O2
4CO2 + 6H2O
remove fraction
multiply both sides by 2
From Chapter 3 section 3.7
12
Balancing Chemical Equations
5. Check to make sure that you have the same
number of each type of atom on both sides of the
equation.
2C2H6 + 7O2
4CO2 + 6H2O
4 C (2 x 2)
4C
12 H (2 x 6)
12 H (6 x 2)
14 O (7 x 2)
14 O (4 x 2 + 6)
Reactants
4C
12 H
14 O
From Chapter 3 section 3.7
Products
4C
12 H
14 O
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Precipitation Reactions
Precipitate – insoluble solid that separates from solution
precipitate
Pb(NO3)2(aq) + 2NaI(aq)
PbI2(s) + 2NaNO3(aq)
molecular equation
Pb2+ + 2NO3- + 2Na+ + 2I-
PbI2(s) + 2Na+ + 2NO3-
ionic equation
Pb2+ + 2IPbI2
PbI2(s)
net ionic equation
Na+ and NO3- are spectator ions
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Precipitation of Lead Iodide
Pb2+ + 2I-
PbI2(s)
PbI2
15
Solubility is the maximum amount of solute that will dissolve
in a given quantity of solvent at a specific temperature.
16
Examples of Insoluble Compounds
CdS
PbS
Ni(OH)2
Al(OH)3
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Writing Net Ionic Equations
1. Write the balanced molecular equation.
2. Write the ionic equation showing the strong electrolytes
completely dissociated into cations and anions.
3. Cancel the spectator ions on both sides of the ionic equation
4. Check that charges and number of atoms are balanced in the
net ionic equation
Write the net ionic equation for the reaction of silver nitrate
with sodium chloride.
AgNO3(aq) + NaCl(aq)
AgCl(s) + NaNO3(aq)
Ag+ + NO3- + Na+ + Cl-
AgCl(s) + Na+ + NO3-
Ag+ + Cl-
AgCl(s)
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Properties of Acids
Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
Cause color changes in plant dyes.
React with certain metals to produce hydrogen gas.
2HCl(aq) + Mg(s)
MgCl2(aq) + H2(g)
React with carbonates and bicarbonates
to produce carbon dioxide gas
2HCl(aq) + CaCO3(s)
CaCl2(aq) + CO2(g) + H2O(l)
Aqueous acid solutions conduct electricity.
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Properties of Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes.
Aqueous base solutions conduct electricity.
Examples:
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Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
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Hydronium ion, hydrated proton, H3O+
22
A Brønsted acid is a proton donor
A Brønsted base is a proton acceptor
base
acid
acid
base
A Brønsted acid must contain at least one ionizable
proton!
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Monoprotic acids
HCl
H+ + Cl-
HNO3
H+ + NO3H+ + CH3COO-
CH3COOH
Strong electrolyte, strong acid
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Diprotic acids
H2SO4
H+ + HSO4-
Strong electrolyte, strong acid
HSO4-
H+ + SO42-
Weak electrolyte, weak acid
Triprotic acids
H3PO4
H2PO4HPO42-
H+ + H2PO4H+ + HPO42H+ + PO43-
Weak electrolyte, weak acid
Weak electrolyte, weak acid
Weak electrolyte, weak acid
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Identify each of the following species as a Brønsted acid, base,
or both. (a) HI, (b) CH3COO-, (c) H2PO4-
HI (aq)
H+ (aq) + I- (aq)
CH3COO- (aq) + H+ (aq)
H2PO4- (aq)
Brønsted acid
CH3COOH (aq)
H+ (aq) + HPO42- (aq)
H2PO4- (aq) + H+ (aq)
H3PO4 (aq)
Brønsted base
Brønsted acid
Brønsted base
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Neutralization Reaction
acid + base
salt + water
HCl(aq) + NaOH(aq)
NaCl(aq) + H2O
H+ + Cl- + Na+ + OH-
Na+ + Cl- + H2O
H+ + OH-
H2O
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Neutralization Reaction Involving a Weak
Electrolyte
weak acid + base
HCN(aq) + NaOH(aq)
HCN + Na+ + OH-
HCN + OH-
salt + water
NaCN(aq) + H2O
Na+ + CN- + H2O
CN- + H2O
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Neutralization Reaction Producing a Gas
acid + base
2HCl(aq) + Na2CO3(aq)
2H+ + 2Cl- + 2Na+ + CO32-
2H+ + CO32-
salt + water + CO2
2NaCl(aq) + H2O +CO2
2Na+ + 2Cl- + H2O + CO2
H2O + CO2
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Oxidation-Reduction Reactions
(electron transfer reactions)
2Mg
O2 + 4e-
2Mg2+ + 4e- Oxidation half-reaction (lose e-)
2O2Reduction half-reaction (gain e-)
2Mg + O2 + 4e2Mg2+ + 2O2- + 4e29
2Mg + O2
2MgO
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Zn(s) + CuSO4(aq)
ZnSO4(aq) + Cu(s)
Zn2+ + 2e- Zn is oxidized
Zn
Cu2+ + 2e-
Zn is the reducing agent
Cu Cu2+ is reduced Cu2+ is the oxidizing agent
Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?
Cu(s) + 2AgNO3(aq)
Cu
Ag+ + 1e-
Cu(NO3)2(aq) + 2Ag(s)
Cu2+ + 2eAg Ag+ is reduced
Ag+ is the oxidizing agent
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Oxidation number
The charge the atom would have in a molecule (or an
ionic compound) if electrons were completely transferred.
1. Free elements (uncombined state) have an oxidation
number of zero.
Na, Be, K, Pb, H2, O2, P4 = 0
2. In monatomic ions, the oxidation number is equal to
the charge on the ion.
Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2
3. The oxidation number of oxygen is usually –2. In H2O2
and O22- it is –1.
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4.4
4. The oxidation number of hydrogen is +1 except when
it is bonded to metals in binary compounds. In these
cases, its oxidation number is –1.
5. Group IA metals are +1, IIA metals are +2 and fluorine is
always –1.
6. The sum of the oxidation numbers of all the atoms in a
molecule or ion is equal to the charge on the
molecule or ion.
7. Oxidation numbers do not have to be integers.
Oxidation number of oxygen in the superoxide ion,
O2-, is –½.
-
HCO3
What are the oxidation numbers
of all the elements in HCO3- ?
O = –2
H = +1
3x(–2) + 1 + ? = –1
C = +4
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The Oxidation Numbers of Elements in their Compounds
34
What are the oxidation numbers of
all the elements in each of these
compounds?
NaIO3
IF7
K2Cr2O7
NaIO3
IF7
F = -1
7x(-1) + ? = 0
I = +7
Na = +1 O = -2
3x(-2) + 1 + ? = 0
I = +5
K2Cr2O7
O = -2
K = +1
7x(-2) + 2x(+1) + 2x(?) = 0
Cr = +6
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Types of Oxidation-Reduction Reactions
Combination Reaction
A+B
0
0
3Mg + N2
C
+2 -3
MgN2
Decomposition Reaction
C
+1 +5 -2
2KClO3
A+B
+1 -1
0
2KCl + 3O2
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Types of Oxidation-Reduction Reactions
Combustion Reaction
A + O2
B
0
0
S + O2
0
0
2Mg + O2
+4 -2
SO2
+2 -2
2MgO
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Types of Oxidation-Reduction Reactions
Displacement Reaction
A + BC
0
+1
+2
Sr + 2H2O
+4
0
TiCl4 + 2Mg
0
AC + B
-1
Cl2 + 2KBr
0
Sr(OH)2 + H2 Hydrogen Displacement
0
+2
Ti + 2MgCl2
-1
Metal Displacement
0
2KCl + Br2
Halogen Displacement
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The Activity Series for Metals
Hydrogen Displacement Reaction
M + BC
MC + B
M is metal
BC is acid or H2O
B is H2
Ca + 2H2O
Ca(OH)2 + H2
Pb + 2H2O
Pb(OH)2 + H2
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The Activity Series for Halogens
F2 > Cl2 > Br2 > I2
Halogen Displacement Reaction
0
-1
Cl2 + 2KBr
I2 + 2KBr
-1
0
2KCl + Br2
2KI + Br2
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Classify each of the following reactions.
Ca2+ + CO32NH3 + H+
Zn + 2HCl
Ca + F2
CaCO3
NH4+
ZnCl2 + H2
CaF2
Precipitation
Acid-Base
Redox (H2 Displacement)
Redox (Combination)
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Gravimetric Analysis
1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
3. Filter and dry precipitate
4. Weigh precipitate
5. Use chemical formula and mass of precipitate to determine
amount of unknown ion
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Titrations
In a titration a solution of accurately known concentration is
added gradually added to another solution of unknown
concentration until the chemical reaction between the two
solutions is complete.
Equivalence point – the point at which the reaction is complete
Indicator – substance that changes color at (or near) the
equivalence point
Slowly add base
to unknown acid
UNTIL
the indicator
changes color
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Titrations can be used in the analysis of
Acid-base reactions
H2SO4 + 2NaOH
2H2O + Na2SO4
Redox reactions
5Fe2+ + MnO4- + 8H+
Mn2+ + 5Fe3+ + 4H2O
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CH-3 (part) and 4 HW
Questions and Problems
Page 91
3.60 & 3.64
Questions and Problems
Pages 129 - 131
4.8, 4.10, 4.12, 4.14, 4.18, 4.20, 4.22, 4.24, 4.32 ,
4.34, 4.40, 4.42, 4.44, 4.46, 4.48, 4.50
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