AP Chemistry Chapter 4 Powerpoint

8/10/2019 AP Chemistry Chapter 4 Powerpoint

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AqueousReactions

2009, Prentice-Hall, Inc.

Chapter 4 Aqueous Reactions and

Solution Stoichiometry

John D. Bookstaver

St. Charles Community CollegeCottleville, MO

Chemistry, The Central Science , 11th editionTheodore L. Brown; H. Eugene LeMay, Jr.;

and Bruce E. Bursten


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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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Dissociation

An electrolyte is asubstances that

dissociates into ionswhen dissolved inwater.


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Electrolytes

An electrolyte is asubstances that

dissociates into ionswhen dissolved inwater.

A nonelectrolyte maydissolve in water, butit does not dissociateinto ions when it doesso.


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Electrolytes andNonelectrolytes

Soluble ioniccompounds tendto be electrolytes.


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Electrolytes andNonelectrolytes

Molecularcompounds 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 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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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 ) + KCl (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


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


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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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

Arrhenius defined basesas substances thatincrease theconcentration of OH when dissolved in water.

Brnsted and Lowrydefined them as proton

acceptors.


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Bases

The strong basesare the soluble

metal salts ofhydroxide 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.

CH3COOH (aq ) + NaOH (aq ) CH

3COONa (aq ) + H

2O (l )


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When a strong acid reacts with a strong base, the netionic equation is

HCl (aq ) + NaOH (aq ) NaCl (aq ) + H2O (l )


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H+ (aq ) + Cl - (aq ) + Na + (aq ) + OH -(aq ) Na + (aq ) + Cl - (aq ) + H 2O (l )


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H+ (aq ) + Cl - (aq ) + Na + (aq ) + OH -(aq ) Na + (aq ) + Cl - (aq ) + H 2O (l )

H+ (aq ) + OH - (aq ) H2O (l )


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Gas-Forming Reactions

Some metathesis reactions do not give theproduct expected.

In this reaction, the expected product (H 2CO 3)decomposes to give a gaseous product(CO 2).

CaCO3

(s ) + HCl (aq ) CaCl2

(aq ) + CO2

(g ) + H2O (l )


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When a carbonate or bicarbonate reacts withan acid, the products are a salt, carbon

dioxide, and water.

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 )


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Similarly, when a sulfite reacts with an acid,the products are a salt, sulfur dioxide, and

water.

SrSO 3 (s ) + 2 HI (aq ) SrI 2 (aq ) + SO 2 (g ) + H 2O (l )


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This reaction gives the predicted product, butyou had better carry it out in the hood, or you

will be very unpopular! But 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.

One cannot occurwithout 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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Displacement Reactions

In displacement reactions,ions oxidize an element.

The ions, then, arereduced.


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In this reaction,silver ions oxidizecopper metal.

Cu (s ) + 2 Ag + (aq ) Cu 2+ (aq ) + 2 Ag (s )


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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

To create a solution of aknown molarity, oneweighs out a known mass(and, therefore, number ofmoles) of the solute.

The solute is added to avolumetric flask, and

solvent is added to the lineon the neck of the flask.


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Dilution

One can also dilute a more concentratedsolution by Using a pipet to deliver a volume of the solution to

a new volumetric flask, and

Adding solvent to the line on the neck of the newflask.


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Dilution

The molarity of the new solution can be determinedfrom the equation

M c V c = M d V d,

where M c and M d are the molarity of the concentrated and dilutesolutions, respectively, and V c and V d are the volumes of thetwo solutions.


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Using Molarities inStoichiometric Calculations


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Titration

Titration is ananalyticaltechnique inwhich one cancalculate theconcentration

of a solute ina solution.

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AP Chemistry Chapter 4 Powerpoint