Chapter 7 Reactions in Aqueous Solutions
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Transcript of Chapter 7 Reactions in Aqueous Solutions
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Chapter 7
Reactions in Aqueous Solutions
Chemistry 101
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Reactions in Aqueous Solutions
Ionic compounds (Salt)
Aqueous solution: solvent is water
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Reactions in Aqueous Solutions
In our body reactions occur in the aqueous solution.
Chemical reactions that occur in water.
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Water in our body
1. About 60% of our body.
2. Most of the reactions occur in aqueous solution.
3. Participates in many biochemical reactions.
4. Transports reactants and products from one place in our body to another.
5. Eliminates the waste materials from cells and our body (urine).
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Why does a chemical reaction occur?
1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
Several driving forces:
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Why does a chemical reaction occur?
Several driving forces:
1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
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Formation of a solid
Precipitation reactions
Precipitate
KI + Pb(NO3)2 ?
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Ionic Compounds
When an ionic compound dissolves in water, ions are produced.
Each ion is surrounded by water molecules.
Ions Hydrated by H2O
Hydration
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Ionic Compounds
1. Soluble solid: it completely dissolves in water (ions are formed).
2. Slightly soluble solid: it partially dissolves in water.
3. Insoluble solid: it does not dissociate in water (almost).
• Note: the terms insoluble and slightly soluble mean such a miniscule amount dissolves that you can’t see any decrease in the amount of solid present.
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Solubility Rules
Memorize these
RULES!
Soluble
Insoluble
Preceding rules trump following rules.
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• Another way of showing the same rules.
Solubility Rules
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+ -
electrolyteNa+Cl-
bulb
Electrolytes
Electrolyte: conducts an electric current.
Ionization (Dissociation)
NaCl → Na+ + Cl-
strong electrolytes: molecules dissociate completely into ions (NaCl).
weak electrolytes: molecules dissociate partially into ions (CH3COOH).
nonelectrolytes: molecules do not dissociate into ions (DI water).
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Formation of a solid
Precipitation reactions
Precipitate
KI + Pb(NO3)2 ?
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Aqueous Solution (ionic compounds)
KI(s) K+(aq) + I-(aq) Dissociation(Ionization)
aqueous solution: solvent is water
H2OKI
Pb(NO3)2
K+
Pb(NO3)2(s) Pb2+(aq) + 2NO3-(aq)
H2O
I-
Pb2+
NO3-
NO3-
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Aqueous Solution (ionic compounds)
KI Pb(NO3)2
K+
I- Pb2+
NO3-
sometimes the ions react with each other.
Positive ions will interact with negative ions.
2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
Sometimes they stick together to form a solid (precipitate).
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2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq) PbI2(s) + 2K+(aq) + 2NO3
-(aq)
CompleteIonic equation:
Molecular equation:
2As3+(aq) + 3s2-(aq) As2S3(s)
total charge on left side = total charge on right sidebalanced equation
2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq) PbI2(s) + 2K+(aq) + 2NO3
-(aq)
Pb2+(aq) + 2I-(aq) PbI2(s)Net ionic equation:
Spectator ions
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Pb(NO3)2(aq) + Na2SO4(aq) ?
Pb(NO3)2(aq) + Na2SO4(aq) PbSO4(s) + NaNO3(aq)
Example
Pb(NO3)2(aq) + Na2SO4(aq) PbSO4(s) + 2 NaNO3(aq)
Balance it:
Pb2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + SO4
2-(aq) PbSO4(s) + 2 Na+(aq) + 2 NO3-(aq)
Complete ionic equation
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Pb2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + SO4
2-(aq) PbSO4(s) + 2 Na+(aq) + 2 NO3-(aq)
• The ions that do not react are called spectator ions.
Example
Net ionic equation: Pb2+(aq) + SO42-(aq) PbSO4(s)
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1. Molecular equation
3 KOH(aq) + Fe(NO3)3(aq) ?
2. Balancing
3. Complete ionic equation
4. Net ionic equation
Practice
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Why does a chemical reaction occur?
1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
Several driving forces:
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Acids and Bases
Acids: sour
Bases: bitter or salty
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Acids and Bases
NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
Acid: produces H3O+ (H+) in water.
Base: produces OH- in water.
Arrhenius definition:
CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)
H3O+ (Hydronium ion): H+(aq) + H2O(l) H3O+(aq)
NaOH(s) Na+(aq) + OH-(aq)H2O
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Acids and Bases
Weak acid and base: it is partially ionized in aqueous solution.
CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)
NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
produces less H+ and OH-
Strong acid and base: it is completely ionized in aqueous solution.
HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq)
NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)
produces more H+ and OH-
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Acid-Base Reactions
Neutralization
NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)
Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) + Na+(aq) + Cl-(aq) + H2O(l)
H+(aq) + OH-(aq) H2O(l)
The only chemical change is the formation of water.
Strong acid + Strong base → Salt + H2O
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Why does a chemical reaction occur?
1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
Several driving forces:
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Na → Na+ + e-
Cl + e- → Cl-
Oxidation and Reduction reactions (redox)
2Na(s) + Cl2(g) 2NaCl(s)
e-
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Oxidation and Reduction reactions (redox)
oxidation: it is the loss of electrons.
reduction: it is the gain of electrons.
Remember – LEO says GER.Loss of Electrons is OxidationGain of Electrons is Reduction.
Na → Na+ + e-
Cl + e- → Cl-
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Metal + Nonmetal : Transfer of electrons
Oxidation and Reduction reactions (redox)
Oxidation and Reduction reactions (redox)
Oxidation and reduction always occur together. (The lost e- must go somewhere!)
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Oxidation and Reduction reactions (redox)
Zn(s) Zn2+(aq) + 2e- Zn is oxidized (reducing agent)
Cu2+(aq) + 2e- Cu(s) Cu2+ is reduced (oxidizing agent)
oxidation: it is the loss of electrons.
reduction: it is the gain of electrons.
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) redox reaction
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Oxidation and Reduction reactions (redox)
oxidation: is the gain of oxygen / loss of hydrogen.
reduction: is the loss of oxygen / gain of hydrogen.
CH4(s) + 2O2(g) CO2(g) + 2H2O(g) redox reaction
C gains O and loses His oxidized
(reducing agent)
O gains HIs reduced
(oxidizing agent)
single replacement reaction and combustion reactions redox reactions
double replacement reactions non redox
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Oxidation and Reduction reactions (redox)
• 2 Al(s) + Fe2O3(s) 2 Fe(s) + Al2O3(s)
• Called the Thermite reaction.
• Let’s just say it’s vigorous!
Example 2:
is oxidized is reduced
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Oxidation and Reduction reactions (redox)
Example 3:
Cu(s) + 2 Ag+(aq) 2 Ag(s) + Cu2+(aq)
is oxidized is reduced
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Zn(s) + 2 HCl(aq) H2(g) + ZnCl2(aq)
Note: this reaction also shows the fourth driving force of a reaction, namely, the formation of a gas.
Example 4:
Oxidation and Reduction reactions (redox)
is oxidized is reduced
Zn(s) + 2 H+(aq) H2(g) + Zn2+(aq)
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2 Mg(s) + O2(g) 2 MgO(s)
Oxidation and Reduction reactions (redox)
Practice:
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Classification of chemical reactions
Chemical reactions
PrecipitationReactions
Oxidation-ReductionReactions
Acid-BaseReactions
CombustionsReactions
Synthesis (combination)
Reactions(Reactants are elements.)
Decomposition (Analysis)
Reactions(Products are elements.)