ch 4 aqueous reactions
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AqueousReactions
Electrolytes
Substances thatdissociate into ions
when dissolved inwater.
A nonelectrolyte maydissolve in water, but it
does not dissociate intoions when it does so.
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AqueousReactions
Electrolytes andNonelectrolytes
Soluble ionic
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Electrolytes andNonelectrolytes
Molecular
compounds tend to benonelectrolytes, exceptfor acids and bases.Click to edit Master text styles
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Electrolytes
A strong electrolytedissociates completelywhen dissolved in water.
A weak electrolyte onlydissociates partiallywhen dissolved in water.
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AqueousReactions
Strong Electrolytes Are…
Strong acids
Strong bases
Soluble ionic salts
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Precipitation Reactions
When one mixes ionsthat form compoundsthat are insoluble (ascould be predicted bythe solubility guidelines),a precipitate is formed.
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Metathesis (Exchange) Reactions
Metathesis comes from a Greek word thatmeans “to transpose”
It appears the ions in the reactant compoundsexchange, or transpose, ions
AgNO3 ( aq ) + KCl ( aq ) AgCl ( s ) + KNO3 ( aq )
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Molecular Equation
The molecular equation lists the reactantsand products in their molecular form.
AgNO3 (aq ) + KCl (aq ) AgCl (s ) + KNO3 (aq )
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Net Ionic Equation
To form the net ionic equation, cross out anything thatdoes not change from the left side of the equation tothe right.
The only things left in the equation are those thingsthat change (i.e., react) during the course of thereaction.
Those things that didn’t change (and were deleted from
the net ionic equation) are called spectator ions.
Ag+ (aq) + NO3 -(aq ) + K+(aq) + Cl -(aq )
AgCl (s ) + K+ (aq) + NO3 -(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 remainsunchanged from the left side to theright side of the equation.
4. Write the net ionic equation with thespecies that remain.
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AqueousReactions
Acids
There are only sevenstrong acids:
•
Hydrochloric (HCl)• Hydrobromic (HBr)• Hydroiodic (HI)• Nitric (HNO3)• Sulfuric (H2SO4)• Chloric (HClO3)• Perchloric (HClO4)
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Bases
The strong basesare the soluble salts of hydroxide ion:
• Alkali metals• Calcium• Strontium• Barium
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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 ) + H2O ( l )
H+ ( aq ) + Cl- (aq) + Na+ ( aq ) + OH- ( aq )
Na+ ( aq ) + Cl- ( aq ) + H2O ( l )
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Neutralization Reactions
Observe thereaction between Milkof Magnesia,Mg(OH)2, and HCl.
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Oxidation-Reduction Reactions
An oxidation occurswhen an atom or ionloses 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 have anoxidation number of 0.
The oxidation number of a monatomic ionis 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.Ø Oxygen has an oxidation number of −2, except in
the peroxide ion in which it has an oxidationnumber of −1.
Ø Hydrogen is −1 when bonded to a metal, +1 whenbonded to a nonmetal.
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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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Displacement Reactions
In this reaction,
silver ions oxidize
copper metal.
Cu (s ) + 2 Ag+ (aq ) Cu2+ (aq ) + 2 Ag (s )
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Displacement Reactions
The reverse reaction,
however, does not
occur.
Cu2+ (aq ) + 2 Ag (s ) Cu (s ) + 2 Ag+ (aq )
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x
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Activity Series
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Molarity
Two solutions can contain the same compoundsbut be quite different because the proportions of those compounds are different.
Molarity is one way to measure theconcentration of a solution.
moles of solutevolume of solution in liters
Molarity ( M ) =
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Using Molarities inStoichiometric Calculations
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Titration
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