Chapter 4 Aqueous Reactions and Solution Stoichiometry

Chapter 4Chapter 4Aqueous Aqueous

Reactions and Reactions and Solution Solution

StoichiometryStoichiometry

Solutions:Solutions:

Homogeneous Homogeneous mixtures of two or mixtures of two or more pure more pure substances.substances.

The The solventsolvent is is present in greatest present in greatest abundance.abundance.

All other substances All other substances are are solutessolutes..

DissociationDissociation

When an ionic When an ionic substance substance dissolves in water, dissolves in water, the solvent pulls the solvent pulls the individual ions the individual ions from the crystal from the crystal and solvates them.and solvates them.

This process is This process is called called dissociationdissociation..

ElectrolytesElectrolytes

Substances that Substances that dissociate into ions dissociate into ions when dissolved in when dissolved in water.water.

AA nonelectrolytenonelectrolyte may dissolve in may dissolve in water, but it does water, but it does not dissociate into not dissociate into ions when it does ions when it does so.so.

Electrolytes and Electrolytes and NonelectrolytesNonelectrolytes

Soluble ionic Soluble ionic compounds compounds tend to be tend to be electrolytes.electrolytes.

Electrolytes and Electrolytes and NonelectrolytesNonelectrolytes

Molecular compounds Molecular compounds tend to be tend to be nonelectrolytes, except nonelectrolytes, except for acids and bases.for acids and bases.

ElectrolytesElectrolytes

A A strongstrong electrolyteelectrolyte dissociates dissociates completely when completely when dissolved in water.dissolved in water.

A A weakweak electrolyteelectrolyte only dissociates only dissociates partially when partially when dissolved in water.dissolved in water.

Strong Electrolytes Are…Strong Electrolytes Are…

Strong acidsStrong acids

Strong Electrolytes Are…Strong Electrolytes Are… Strong acidsStrong acids Strong basesStrong bases

Strong Electrolytes Are…Strong Electrolytes Are… Strong acidsStrong acids Strong basesStrong bases Soluble ionic saltsSoluble ionic salts

Precipitation ReactionsPrecipitation Reactions

When one mixes When one mixes ions that form ions that form compounds that compounds that are insoluble (as are insoluble (as could be predicted could be predicted by the solubility by the solubility guidelines), a guidelines), a precipitate is precipitate is formed.formed.

Metathesis (Exchange) Metathesis (Exchange) ReactionsReactions

Metathesis comes from a Metathesis comes from a Greek word that means “to Greek word that means “to transpose”transpose”

AgNOAgNO3 (3 (aqaq)) + KCl + KCl ( (aqaq) ) AgClAgCl ( (ss)) + KNO + KNO3 (3 (aqaq))

Metathesis (Exchange) Metathesis (Exchange) ReactionsReactions

Metathesis comes from a Greek word Metathesis comes from a Greek word that means “to transpose”that means “to transpose”

It appears the ions in the reactant It appears the ions in the reactant compounds exchange, or transpose, compounds exchange, or transpose, ionsions

AgAgNONO3 3 ((aqaq)) + + KKClCl ( (aqaq)) AgClAgCl ( (ss)) ++ KNOKNO3 (3 (aqaq))

Solution ChemistrySolution Chemistry

It is helpful to pay attention to It is helpful to pay attention to exactlyexactly what species are present in a what species are present in a reaction mixture (i.e., solid, liquid, reaction mixture (i.e., solid, liquid, gas, aqueous solution).gas, aqueous solution).

If we are to understand reactivity, If we are to understand reactivity, we must be aware of just what is we must be aware of just what is changing during the course of a changing during the course of a reaction.reaction.

Molecular EquationMolecular Equation

The molecular equation lists the The molecular equation lists the reactants and products in their molecular reactants and products in their molecular form.form.

AgNOAgNO3 3 ((aqaq)) + KCl + KCl ((aqaq)) AgCl AgCl ((ss)) + KNO + KNO3 3 ((aqaq))

Ionic EquationIonic Equation In the ionic equation all strong electrolytes In the ionic equation all strong electrolytes

(strong acids, strong bases, and soluble ionic (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.salts) are dissociated into their ions.

This more accurately reflects the species This more accurately reflects the species that are found in the reaction mixture.that are found in the reaction mixture.

AgAg++ ((aqaq) + ) + NONO33- - ((aqaq) + ) + KK++ ( (aqaq) + ) + ClCl- - ((aqaq) )

AgClAgCl ((ss) + ) + KK++ ((aqaq) + NO) + NO33- - ((aqaq))

Net Ionic EquationNet Ionic Equation To form the net ionic equation, cross out To form the net ionic equation, cross out

anything that does not change from the left anything that does not change from the left side of the equation to the right.side of the equation to the right.

AgAg++(aq)(aq) + NO + NO33--((aqaq)) + K + K++(aq)(aq) + Cl + Cl--((aqaq))

AgClAgCl ((ss)) + K + K++(aq)(aq) + NO + NO33--((aqaq))



The only things left in the equation are those The only things left in the equation are those things that change (i.e., react) during the things that change (i.e., react) during the course of the reaction.course of the reaction.

AgAg++(aq)(aq) + Cl + Cl--((aqaq)) AgCl AgCl ((ss))



The only things left in the equation are those The only things left in the equation are those things that change (i.e., react) during the things that change (i.e., react) during the course of the reaction.course of the reaction.

Those things that didn’t change (and were Those things that didn’t change (and were deleted from the net ionic equation) are deleted from the net ionic equation) are called called spectatorspectator ionsions..

AgAg++(aq)(aq) + NO + NO33--((aqaq)) + K + K++

(aq)(aq) + Cl + Cl--((aqaq))

AgClAgCl ((ss)) + K + K++(aq)(aq) + NO + NO33--((aqaq))

Writing Net Ionic Writing Net Ionic EquationsEquations

1.1. Write a balanced molecular Write a balanced molecular equation.equation.

2.2. Dissociate all strong electrolytes.Dissociate all strong electrolytes.

3.3. Cross out anything that remains Cross out anything that remains unchanged from the left side to unchanged from the left side to the right side of the equation.the right side of the equation.

4.4. Write the net ionic equation with Write the net ionic equation with the species that remain.the species that remain.

Writing Net Ionic Writing Net Ionic EquationsEquations

Acids:Acids:

Substances that Substances that increase the increase the concentration of Hconcentration of H++ when dissolved in when dissolved in water (Arrhenius).water (Arrhenius).

Proton donors Proton donors (Brønsted(Brønsted––Lowry).Lowry).

AcidsAcids

There are only There are only seven strong acids:seven strong acids:• Hydrochloric (HCl)Hydrochloric (HCl)• Hydrobromic (HBr)Hydrobromic (HBr)• Hydroiodic (HI)Hydroiodic (HI)• Nitric (HNONitric (HNO33))

• Sulfuric (HSulfuric (H22SOSO44))

• Chloric (HClOChloric (HClO33))

• Perchloric (HClOPerchloric (HClO44))

Bases:Bases:

Substances that Substances that increase the increase the concentration of concentration of OHOH−− when when dissolved in water dissolved in water (Arrhenius).(Arrhenius).

Proton acceptors Proton acceptors (Brønsted(Brønsted––Lowry).Lowry).

BasesBases

The strong bases The strong bases are the soluble are the soluble salts of hydroxide salts of hydroxide ion:ion:• Alkali metalsAlkali metals• CalciumCalcium• StrontiumStrontium• BariumBarium

Acid-Base ReactionsAcid-Base Reactions

In an acid-base In an acid-base reaction, the acid reaction, the acid donates a proton donates a proton (H(H++) to the base.) to the base.

Neutralization ReactionsNeutralization ReactionsGenerally, when solutions of an acid and a base Generally, when solutions of an acid and a base are combined, the products are a salt and are combined, the products are a salt and water.water.

HCl HCl ((aqaq)) + NaOH + NaOH ((aqaq) ) NaCl NaCl ((aqaq)) + H + H22O O ((ll))

Neutralization ReactionsNeutralization ReactionsWhen a strong acid reacts with a strong base, When a strong acid reacts with a strong base,

the net ionic equation is…the net ionic equation is…

HCl HCl ((aqaq)) + NaOH + NaOH ((aqaq) ) NaCl NaCl ((aqaq)) + H + H22O O ((ll))

HH+ + ((aqaq)) + Cl+ Cl- - ((aqaq)) + Na+ Na+ + ((aqaq) + OH) + OH--((aqaq))

NaNa+ + ((aqaq)) + Cl+ Cl- - ((aqaq)) + H+ H22O (O (ll))

Neutralization ReactionsNeutralization ReactionsWhen a strong acid reacts with a strong base, When a strong acid reacts with a strong base,

the net ionic equation is…the net ionic equation is…

HCl (HCl (aqaq) + NaOH () + NaOH (aqaq) ) NaCl ( NaCl (aqaq) + H) + H22O (O (ll) )

HH+ + ((aqaq) + Cl) + Cl- - ((aqaq) + Na) + Na+ + ((aqaq) + OH) + OH--((aqaq)) Na Na+ + ((aqaq) + Cl) + Cl- -

((aqaq) + H) + H22O (O (ll))

HH+ + ((aqaq) + Cl) + Cl- - ((aq)aq) + Na + Na+ + ((aqaq) + OH) + OH- - ((aqaq) ) Na Na+ + ((aqaq) + Cl) + Cl- -

((aqaq) + H) + H22O (O (ll))

Neutralization ReactionsNeutralization Reactions

Observe the Observe the reaction between reaction between Milk of Magnesia, Milk of Magnesia, Mg(OH)Mg(OH)22, and HCl., and HCl.

Gas-Forming ReactionsGas-Forming Reactions

These metathesis reactions do not give These metathesis reactions do not give the product expected.the product expected.

The expected product decomposes to give The expected product decomposes to give a gaseous product (COa gaseous product (CO22 or SO or SO22).).

CaCOCaCO3 3 ((ss)) + HCl + HCl ((aqaq) ) CaClCaCl2 2 ((aqaq)) + CO + CO2 2 ((gg)) + H + H22O O ((ll))

NaHCONaHCO3 3 ((aqaq)) + HBr + HBr ((aqaq) ) NaBr NaBr ((aqaq)) + CO+ CO2 2 ((gg)) + H + H22O O ((ll))

SrSOSrSO3 3 ((ss)) + 2 HI + 2 HI ((aqaq)) SrISrI2 2 ((aqaq)) + SO + SO2 2 ((gg)) + H + H22O O ((ll))

Gas-Forming ReactionsGas-Forming Reactions

This reaction gives the predicted product, This reaction gives the predicted product, but you had better carry it out in the but you had better carry it out in the hood, or you will be very unpopular!hood, or you will be very unpopular!

Just as in the previous examples, a gas is Just as in the previous examples, a gas is formed as a product of this reaction:formed as a product of this reaction:

NaNa22S S ((aqaq)) + H + H22SOSO4 4 ((aqaq)) Na Na22SOSO4 4 ((aqaq)) + H + H22S S ((gg) )

Oxidation-Reduction Oxidation-Reduction ReactionsReactions

An An oxidationoxidation occurs when an occurs when an atom or ion atom or ion losesloses electrons.electrons.

A A reductionreduction occurs occurs when an atom or when an atom or ion ion gainsgains electrons.electrons.

Oxidation-Reduction Oxidation-Reduction ReactionsReactions

One cannot One cannot occur without occur without the other.the other.

Oxidation NumbersOxidation Numbers

To determine if an oxidation-To determine if an oxidation-reduction reaction has reduction reaction has occurred, we assign an occurred, we assign an oxidation numberoxidation number to each to each element in a neutral element in a neutral compound or charged entity.compound or charged entity.


Elements in their elemental form Elements in their elemental form have an oxidation number of 0.have an oxidation number of 0.

The oxidation number of a The oxidation number of a monatomic ion is the same as its monatomic ion is the same as its charge.charge.


Nonmetals tend to have negative Nonmetals tend to have negative oxidation numbers, although some oxidation numbers, although some are positive in certain compounds are positive in certain compounds or ions.or ions. Oxygen has an oxidation number of Oxygen has an oxidation number of

−−2, except in the peroxide ion in which 2, except in the peroxide ion in which it has an oxidation number of it has an oxidation number of −−1.1.

Hydrogen is Hydrogen is −−1 when bonded to a 1 when bonded to a metal, +1 when bonded to a nonmetal.metal, +1 when bonded to a nonmetal.

Oxidation NumbersOxidation Numbers Nonmetals tend to have negative Nonmetals tend to have negative

oxidation numbers, although some oxidation numbers, although some are positive in certain compounds or are positive in certain compounds or ions.ions. Fluorine always has an oxidation Fluorine always has an oxidation

number of number of −−1.1. The other halogens have an oxidation The other halogens have an oxidation

number of number of −−1 when they are negative; 1 when they are negative; they can have positive oxidation they can have positive oxidation numbers, however, most notably in numbers, however, most notably in oxyanions.oxyanions.


The sum of the oxidation The sum of the oxidation numbers in a neutral numbers in a neutral compound is 0.compound is 0.

The sum of the oxidation The sum of the oxidation numbers in a polyatomic ion is numbers in a polyatomic ion is the charge on the ion.the charge on the ion.

Displacement ReactionsDisplacement Reactions

In In displacement displacement reactions, ions reactions, ions oxidize an oxidize an element.element.

The ions, then, The ions, then, are reduced.are reduced.


In this reaction, In this reaction, silver ions oxidize silver ions oxidize copper metal.copper metal.

Cu Cu ((ss)) + 2 Ag + 2 Ag+ + ((aqaq)) Cu Cu2+ 2+ ((aqaq)) + 2 Ag + 2 Ag ((ss))


The reverse reaction, The reverse reaction,

however, does not however, does not

occur.occur.

CuCu2+ 2+ ((aqaq)) + 2 Ag + 2 Ag ((ss)) Cu Cu ((ss)) + 2 Ag + 2 Ag+ + ((aqaq) ) x

Activity SeriesActivity Series

MolarityMolarity Two solutions can contain the same Two solutions can contain the same

compounds but be quite different compounds but be quite different because the proportions of those because the proportions of those compounds are different.compounds are different.

Molarity is one way to measure the Molarity is one way to measure the concentration of a solution.concentration of a solution.

moles of solute

volume of solution in litersMolarity (M) =

Mixing a SolutionMixing a Solution

DilutionDilution

Using Molarities inUsing Molarities inStoichiometric CalculationsStoichiometric Calculations

TitrationTitrationThe analytical The analytical technique in technique in which one can which one can calculate the calculate the concentration concentration of a solute in a of a solute in a solution.solution.

TitrationTitration

Chapter 4 Aqueous Reactions and Solution Stoichiometry

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