Download Chapter 4

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Reactions in Aqueous Solution
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Chapter 4
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For test 3:
Sections 3.7 and 4.1 to 4.5
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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A solution is a homogenous mixture of 2 or more
substances
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The solute is(are) the substance(s) present in the
smaller amount(s)
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The solvent is the substance present in the larger
amount
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Solution
Solvent
Solute
Soft drink(l)
H2O
Sugar, CO2
Air(g)
N2
O2, Ar, CH4
Soft Solder(s)
Pb
Sn
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aqueous solutions
of KMnO4
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An electrolyte is a substance that, when dissolved in
water, results in a solution that can conduct electricity.
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A nonelectrolyte is a substance that, when dissolved,
results in a solution that does not conduct electricity.
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nonelectrolyte
weak electrolyte
strong electrolyte
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Conduct electricity in solution?
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Cations (+) and Anions (-)
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Strong Electrolyte – 100% dissociation
NaCl(s)
H2O
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Na+(aq) + Cl-(aq)
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Weak Electrolyte – not completely dissociated
CH3COOH
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CH3COO-(aq) + H+(aq)
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Ionization of acetic acid
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CH3COOH
CH3COO-(aq) + H+(aq)
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A reversible reaction. The reaction can
occur in both directions.
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Acetic acid is a weak electrolyte because its
ionization in water is incomplete.
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Hydration is the process in which an ion is surrounded
by water molecules arranged in a specific manner.
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d-
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d+
H2O
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Nonelectrolyte does not conduct electricity?
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No cations (+) and anions (-) in solution
C6H12O6(s)
H2O
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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
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products
3 ways of representing the reaction of H2 with O2 to form H2O
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From Chapter 3 section 3.7
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How to “Read” Chemical Equations
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2 Mg + O2
2 MgO
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2 atoms Mg + 1 molecule O2 makes 2 formula units MgO
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2 moles Mg + 1 mole O2 makes 2 moles MgO
48.6 grams Mg + 32.0 grams O2 makes 80.6 g MgO
NOT
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2 grams Mg + 1 gram O2 makes 2 g MgO
From Chapter 3 section 3.7
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Balancing Chemical Equations
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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.
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Ethane reacts with oxygen to form carbon dioxide and water
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C2H6 + O2
CO2 + H2O
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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
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Balancing Chemical Equations
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3. Start by balancing those elements that appear in
only one reactant and one product.
C2H6 + O2
CO2 + H2O
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start with C or H but not O
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1 carbon
on right
2 carbon
on left
C2H6 + O2
6 hydrogen
on left
C2H6 + O2
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multiply CO2 by 2
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2CO2 + H2O
2 hydrogen
on right
2CO2 + 3H2O
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multiply H2O by 3
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From Chapter 3 section 3.7
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Balancing Chemical Equations
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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
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4 oxygen + 3 oxygen = 7 oxygen
(3x1)
on right
(2x2)
C2H6 + 7 O2
2
2CO2 + 3H2O
2C2H6 + 7O2
4CO2 + 6H2O
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remove fraction
multiply both sides by 2
From Chapter 3 section 3.7
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Balancing Chemical Equations
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5. Check to make sure that you have the same
number of each type of atom on both sides of the
equation.
2C2H6 + 7O2
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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)
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Reactants
Products
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4C
12 H
14 O
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4C
12 H
14 O
From Chapter 3 section 3.7
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Precipitation Reactions
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Precipitate – insoluble solid that separates from solution
precipitate
Pb(NO3)2(aq) + 2NaI(aq)
Pb2+ + 2NO3- + 2Na+ + 2I-
PbI2(s) + 2NaNO3(aq)
PbI2(s) + 2Na+ + 2NO3-
ionic equation
Pb2+
PbI2
+
2I-
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molecular equation
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PbI2(s)
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net ionic equation
Na+ and NO3- are spectator ions
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Precipitation of Lead Iodide
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Pb2+ + 2I-
PbI2(s)
PbI2
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Solubility is the maximum amount of solute that will dissolve
in a given quantity of solvent at a specific temperature.
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Examples of Insoluble Compounds
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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.
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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
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Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
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Cause color changes in plant dyes.
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React with certain metals to produce hydrogen gas.
2HCl(aq) + Mg(s)
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MgCl2(aq) + H2(g)
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React with carbonates and bicarbonates
to produce carbon dioxide gas
2HCl(aq) + CaCO3(s)
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CaCl2(aq) + CO2(g) + H2O(l)
Aqueous acid solutions conduct electricity.
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Properties of Bases
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Have a bitter taste.
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Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes.
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Aqueous base solutions conduct electricity.
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Examples:
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Arrhenius acid is a substance that produces H+ (H3O+) in water
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Arrhenius base is a substance that produces OH- in water
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Hydronium ion, hydrated proton, H3O+
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A Brønsted acid is a proton donor
A Brønsted base is a proton acceptor
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base
acid
acid
base
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A Brønsted acid must contain at least one ionizable
proton!
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Monoprotic acids
HCl
H+ + Cl-
HNO3
H+
+
Strong electrolyte, strong acid
NO3H+
CH3COOH
+
Strong electrolyte, strong acid
CH3COO-
Weak electrolyte, weak acid
Diprotic acids
H2SO4
HSO4-
H+ + SO42-
+
HSO4-
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Triprotic acids
H3PO4
H2PO4HPO42-
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H+
H+
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+ H2PO4H+ + HPO42H+ + PO43-
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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-
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H+ (aq) + I- (aq)
HI (aq)
Brønsted acid
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CH3COO-
H+
(aq) +
(aq)
CH3COOH (aq)
Brønsted base
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H2PO4- (aq)
H2PO4-
H+ (aq) + HPO42- (aq)
(aq) +
H+
(aq)
H3PO4 (aq)
Brønsted acid
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Brønsted base
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Neutralization Reaction
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acid + base
salt + water
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HCl(aq) + NaOH(aq)
NaCl(aq) + H2O
H+ + Cl- + Na+ + OH-
Na+ + Cl- + H2O
H+ + OH-
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H2O
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Neutralization Reaction Involving a Weak
Electrolyte
weak acid + base
salt + water
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HCN(aq) + NaOH(aq)
HCN + Na+ + OHHCN + OH-
NaCN(aq) + H2O
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Na+ + CN- + H2O
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CN- + H2O
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Neutralization Reaction Producing a Gas
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acid + base
2HCl(aq) + Na2CO3(aq)
salt + water + CO2
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2NaCl(aq) + H2O +CO2
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2H+ + 2Cl- + 2Na+ + CO322H+ + CO32-
2Na+ + 2Cl- + H2O + CO2
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H2O + CO2
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Oxidation-Reduction Reactions
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(electron transfer reactions)
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2Mg2+ + 4e- Oxidation half-reaction (lose e-)
O2 + 4e2O2Reduction half-reaction (gain e-)
2Mg + O2 + 4e2Mg2+ + 2O2- + 4e29
2Mg + O2
2MgO
2Mg
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Zn(s) + CuSO4(aq)
ZnSO4(aq) + Cu(s)
Zn2+ + 2e- Zn is oxidized
Zn
Cu2+ + 2e-
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Zn is the reducing agent
Cu Cu2+ is reduced Cu2+ is the oxidizing agent
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Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?
Cu(s) + 2AgNO3(aq)
Cu2+
Cu
Ag+ + 1e-
+
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Cu(NO3)2(aq) + 2Ag(s)
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2e-
Ag Ag+ is reduced
Ag+ is the oxidizing agent
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Oxidation number
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The charge the atom would have in a molecule (or an
ionic compound) if electrons were completely transferred.
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1. Free elements (uncombined state) have an oxidation
number of zero.
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Na, Be, K, Pb, H2, O2, P4 = 0
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2. In monatomic ions, the oxidation number is equal to
the charge on the ion.
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Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2
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3. The oxidation number of oxygen is usually –2. In H2O2
and O22- it is –1.
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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
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H = +1
3x(–2) + 1 + ? = –1
C = +4
4.4
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The Oxidation Numbers of Elements in their Compounds
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IF7
What are the oxidation numbers of
all the elements in each of these
compounds?
NaIO3
IF7
K2Cr2O7
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F = -1
7x(-1) + ? = 0
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I = +7
NaIO3
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Na = +1 O = -2
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K2Cr2O7
3x(-2) + 1 + ? = 0
O = -2
I = +5
K = +1
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7x(-2) + 2x(+1) + 2x(?) = 0
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Cr = +6
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Types of Oxidation-Reduction Reactions
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Combination Reaction
A+ B
0
0
3Mg + N2
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C
+2 -3
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MgN2
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Decomposition Reaction
C
+1 +5 -2
2KClO3
A+ B
+1 -1
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0
2KCl + 3O2
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Types of Oxidation-Reduction Reactions
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Combustion Reaction
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A + O2
B
0
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+4 -2
0
S + O2
SO2
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0
+2 -2
0
2Mg + O2
2MgO
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Types of Oxidation-Reduction Reactions
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Displacement Reaction
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A + BC
0
+1
+2
Sr + 2H2O
+4
0
TiCl4 + 2Mg
0
AC + B
-1
Cl2 + 2KBr
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0
Sr(OH)2 + H2 Hydrogen Displacement
0
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+2
Ti + 2MgCl2
-1
Metal Displacement
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0
2KCl + Br2
Halogen Displacement
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The Activity Series for Metals
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Hydrogen Displacement Reaction
M + BC
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MC + B
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M is metal
BC is acid or H2O
B is H2
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Ca + 2H2O
Ca(OH)2 + H2
Pb + 2H2O
Pb(OH)2 + H2
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The Activity Series for Halogens
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F2 > Cl2 > Br2 > I2
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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+ + CO32-
NH3 + H+
Zn + 2HCl
Ca + F2
CaCO3
NH4+
ZnCl2 + H2
CaF2
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Precipitation
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Acid-Base
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Redox (H2 Displacement)
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Redox (Combination)
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Gravimetric Analysis
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1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
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3. Filter and dry precipitate
4. Weigh precipitate
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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.
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Equivalence point – the point at which the reaction is complete
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Indicator – substance that changes color at (or near) the
equivalence point
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Slowly add base
to unknown acid
UNTIL
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the indicator
changes color
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Titrations can be used in the analysis of
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Acid-base reactions
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H2SO4 + 2NaOH
2H2O + Na2SO4
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Redox reactions
5Fe2+ + MnO4- + 8H+
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Mn2+ + 5Fe3+ + 4H2O
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CH-3 (part) and 4 HW
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Questions and Problems
Page 91
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3.60 & 3.64
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Questions and Problems
Pages 129 - 131
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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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