ch 4 aqueous reactions

8/3/2019 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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Electrolytes andNonelectrolytes

Soluble ionic

compounds tend tobe electrolytes.Click to edit Master text stylesSecond level

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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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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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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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AqueousReactions

Titration



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ch 4 aqueous reactions

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