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8/10/2019 Aqueous Reactions and Stoichiometry Lecture
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AqueousReactions
Chapter 4 Aqueous Reactions and
Solution StoichiometryJohn D. Bookstaver
St. Charles Community CollegeSt. Peters, MO
2006, Prentice Hall, Inc.
Chemistry, The Central Science , 10th editionTheodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
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Solutions:
Homogeneousmixtures of two ormore pure
substances. The solvent is
present in greatestabundance.
All other substancesare solutes .
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Dissociation
When an ionicsubstance dissolves
in water, the solventpulls the individualions from the crystaland solvates them.
This process is calleddissociation .
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Electrolytes
Substances thatdissociate into ions
when dissolved inwater. A nonelectrolyte may
dissolve in water, butit does not dissociateinto ions when it doesso.
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Electrolytes andNonelectrolytes
Soluble ionic
compounds tendto be electrolytes.
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Electrolytes andNonelectrolytes
Molecular
compounds tend tobe nonelectrolytes,except for acids andbases.
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Electrolytes
A strong electrolyte dissociates completely
when dissolved inwater. A weak electrolyte
only dissociatespartially whendissolved in water.
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Strong Electrolytes Are
Strong acids
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Strong Electrolytes Are
Strong acids Strong bases
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Strong Electrolytes Are
Strong acids Strong bases Soluble ionic salts
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Precipitation Reactions
When one mixes ionsthat form compounds
that are insoluble (ascould be predicted bythe solubilityguidelines), a
precipitate is formed.
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Metathesis (Exchange) Reactions
Metathesis comes from a Greek word thatmeans to transpose
AgNO 3 ( aq ) + KCl (aq ) AgCl (s ) + KNO 3 ( aq )
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AqueousReactions
Metathesis (Exchange) Reactions
Metathesis comes from a Greek word thatmeans to transpose
It appears the ions in the reactantcompounds exchange, or transpose, ions
Ag NO 3 ( aq ) + K Cl (aq ) AgCl (s ) + KNO 3 ( aq )
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AqueousReactions
Metathesis (Exchange) Reactions
Metathesis comes from a Greek word thatmeans to transpose
It appears the ions in the reactantcompounds exchange, or transpose, ions
Ag NO 3 ( aq ) + K Cl (aq ) AgCl (s ) + KNO 3 ( aq )
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Solution Chemistry
It is helpful to pay attention to exactly what species are present in a reaction
mixture (i.e., solid, liquid, gas, aqueoussolution).
If we are to understand reactivity, we
must be aware of just what is changingduring the course of a reaction.
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Molecular Equation
The molecular equation lists the reactantsand products in their molecular form.
AgNO 3 (aq ) + KCl (aq ) AgCl (s ) + KNO 3 (aq )
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Ionic Equation
In the ionic equation all strong electrolytes (strongacids, strong bases, and soluble ionic salts) aredissociated into their ions.
This more accurately reflects the species that arefound in the reaction mixture.
Ag+
(aq ) + NO 3-
(aq ) + K+
(aq ) + Cl-
(aq )
AgCl (s ) + K+ (aq ) + NO 3- (aq )
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Net Ionic Equation
To form the net ionic equation, cross out anythingthat does not change from the left side of theequation to the right.
Ag +(aq) + NO 3-(aq ) + K +(aq) + Cl -(aq )
AgCl (s ) + K +(aq) + NO 3-(aq )
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Net Ionic Equation
To form the net ionic equation, cross out anythingthat does not change from the left side of theequation to the right.
The only things left in the equation are those thingsthat change (i.e., react) during the course of thereaction.
Ag +(aq) + Cl -(aq ) AgCl (s )
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Net Ionic Equation
To form the net ionic equation, cross out anythingthat does not change from the left side of theequation to the right.
The only things left in the equation are those thingsthat change (i.e., react) during the course of thereaction.
Those things that didnt change (and were deleted
from the net ionic equation) are called spectator ions .
Ag +(aq) + NO 3-(aq ) + K +(aq) + Cl
-(aq ) AgCl (s ) + K +(aq) + NO 3
-(aq )
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Writing Net Ionic Equations
1. Write a balanced molecular equation.2. Dissociate all strong electrolytes.3. Cross out anything that remains
unchanged from the left side to theright side of the equation.
4. Write the net ionic equation with thespecies that remain.
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Writing Net Ionic Equations
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Acids:
Substances thatincrease the
concentration of H+
when dissolved inwater (Arrhenius).
Proton donors(Brnsted Lowry).
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Acids
There are only sevenstrong acids:
Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO 3)
Sulfuric (H 2SO 4) Chloric (HClO 3) Perchloric (HClO 4)
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Bases:
Substances thatincrease the
concentration ofOH when dissolvedin water (Arrhenius).
Proton acceptors(Brnsted Lowry).
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Bases
The strong basesare the soluble salts
of hydroxide ion: Alkali metals Calcium Strontium
Barium
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Acid-Base Reactions
In an acid-basereaction, the acid
donates a proton(H+) to the base.
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Neutralization Reactions
Generally, when solutions of an acid and a base arecombined, the products are a salt and water.
HCl (aq ) + NaOH (aq ) NaCl (aq ) + H2O (l )
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Neutralization Reactions
When a strong acid reacts with a strong base, the netionic equation is
HCl (aq ) + NaOH (aq ) NaCl (aq ) + H2O (l )
H+ (aq ) + Cl - (aq ) + Na + (aq ) + OH -(aq ) Na + (aq ) + Cl - (aq ) + H 2O ( l )
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Neutralization Reactions
When a strong acid reacts with a strong base, the netionic equation is
HCl (aq ) + NaOH (aq ) NaCl (aq ) + H2O (l )
H+ (aq ) + Cl - (aq ) + Na + (aq ) + OH -(aq ) Na + (aq ) + Cl - (aq ) + H 2O ( l )
H+ (aq ) + Cl - (aq) + Na + (aq ) + OH - (aq ) Na + (aq ) + Cl - (aq ) + H 2O ( l )
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Neutralization Reactions
Observe thereaction between
Milk of Magnesia,Mg(OH) 2, and HCl.
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Gas-Forming Reactions
These metathesis reactions do not give theproduct expected.
The expected product decomposes to give agaseous product (CO 2 or SO 2).
CaCO 3 (s ) + HCl (aq ) CaCl 2 (aq ) + CO 2 (g ) + H 2O (l ) NaHCO 3 (aq ) + HBr (aq ) NaBr (aq ) + CO 2 (g ) + H 2O (l )
SrSO 3 (s ) + 2 HI (aq ) SrI 2 (aq ) + SO 2 (g ) + H 2O (l )
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Gas-Forming Reactions
This reaction gives the predicted product, butyou had better carry it out in the hood, or you
will be very unpopular! Just as in the previous examples, a gas isformed as a product of this reaction:
Na 2S (aq ) + H 2SO 4 (aq ) Na 2SO 4 (aq ) + H 2S (g )
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Oxidation-Reduction Reactions
An oxidation occurswhen an atom or ion
loses electrons. A reduction occurswhen an atom or iongains electrons.
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Oxidation-Reduction Reactions
One cannot occur
without the other.
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Oxidation Numbers
To determine if an oxidation-reductionreaction has occurred, we assign an
oxidation number to each element in aneutral compound or charged entity.
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Oxidation Numbers
Elements in their elemental form havean oxidation number of 0.
The oxidation number of a monatomicion is the same as its charge.
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Oxidation Numbers
Nonmetals tend to have negativeoxidation numbers, although some are
positive in certain compounds or ions.Oxygen has an oxidation number of 2,except in the peroxide ion in which it hasan oxidation number of 1.Hydrogen is 1 when bonded to a metal,+1 when bonded to a nonmetal.
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Oxidation Numbers
Nonmetals tend to have negativeoxidation numbers, although some are
positive in certain compounds or ions.Fluorine always has an oxidation numberof 1.
The other halogens have an oxidationnumber of 1 when they are negative; theycan have positive oxidation numbers,however, most notably in oxyanions.
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Oxidation Numbers
The sum of the oxidation numbers in aneutral compound is 0.
The sum of the oxidation numbers in apolyatomic ion is the charge on the ion.
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Oxidation Numbers
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Displacement Reactions
In displacementreactions, ions
oxidize an element. The ions, then, arereduced.
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Displacement Reactions
In this reaction,silver ions oxidizecopper metal.
Cu (s ) + 2 Ag + (aq ) Cu 2+ (aq ) + 2 Ag (s )
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Displacement Reactions
The reverse reaction,however, does notoccur.
Cu 2+ (aq ) + 2 Ag (s ) Cu (s ) + 2 Ag + (aq )x
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Activity Series
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Molarity
Two solutions can contain the samecompounds but be quite different because theproportions of those compounds are different.
Molarity is one way to measure theconcentration of a solution.
moles of solutevolume of solution in litersMolarity ( M ) =
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Mixing a Solution
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Dilution
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Using Molarities inStoichiometric Calculations
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Titration
The analyticaltechnique inwhich one cancalculate theconcentration ofa solute in asolution.
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Titration