AP Chapter 4 Aqueous Reactions and Solutions HW: 1 5 7 17 21 23 27 31 39 51 55 61 67 80 87 94 100 106 109

AP Chapter 4Aqueous Reactions and Solutions

HW: 1 5 7 17 21 23 27 31 39 51 55 61 67 80 87 94 100 106 109

4.1 – General Solution PropertiesSolution – Homogeneous mixture

-Aqueous Solution – Solvent is waterSolvent – One of larger amountSolute – One of smaller amountElectrolyte – Substance that conducts electricity

when dissolved in water. Dissociates into ions (ex-ionic, acids, bases)

Nonelectrolyte – Substance that does not conduct electricity when dissolved in water (most molecular compounds)

http://www.youtube.com/watch?v=NdG3wK9kNcg

Electrolytes

Open File “SALT WATER CONDUCTIVITY” in AP Power Point folder using Real Player



Ionic Compounds in Water• Dissociates = Each ion separates from the solid

structure and disperses through the solution.• Solvation = Ions become surrounded by water

molecules. Prevents the ions from recombining. When water is the solvent, AKA hydration.

http://www.mpcfaculty.net/mark_bishop/NaCl_dissolves.htm

Ionic Compounds in Water

• Dissociates = Each ion separates from the solid structure and disperses through the solution.

• Solvation = Ions become surrounded by water molecules. Prevents the ions from recombining.

Molecular Compounds in Water

Ionization = Become ions, especially when dissolving in water. Used typically referring to molecular electrolytes.

HCl(g) H+(aq) + Cl-(aq)H2O

© 2009, Prentice-Hall, Inc.

Electrolytes• A strong electrolyte dissociates completely when

dissolved in water.• A weak electrolyte only dissociates partially when

dissolved in water.


Strong Electrolytes Are…

• Strong acids• Strong bases• Soluble ionic

salts

Reversible Reaction – Reaction can proceed in both directions

Chemical Equilibrium – No net change in reaction direction. Activity continues on a molecular level.

General Information

Chapter 18

Chemical Equilibrium

http://www.learner.org/resources/series61.html?pop=yes&pid=806# - Molecules in Action Starting at 15:30-23:52

(FYI: Co(H2O)6+2 + 4Cl- -> CoCl4 + 6 H2O)

Equilibrium

http://www.learner.org/resources/series61.html?pop=yes&pid=806

http://www.learner.org/resources/series61.html?pop=yes&pid=806

http://www.learner.org/vod/vod_window.html?pid=806


4.2 - Precipitation Reactions

Mixing of two ionic solutions that have ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), forms a precipitate.

4.2 – Precipitation Reactions

Precipitation Rxn – Results in a precipitatePrecipitate – Insoluble solid (typically formed

from two solutions)

http://chemed.chem.purdue.edu/demos/main_pages/18.3.html

http://www.youtube.com/watch?v=SuoN0hQPeMw

4.2 – Precipitation ReactionsSolubility – The maximum

amount of solute that will dissolve in a given quantity of solvent at a specific temp

Insoluble – A substance that does not dissolve. Specifically, the solubility must be less than 0.01 mol/L to be considered insoluble.

Solubility RulesSolubility Rules

1. Group 1 & Ammonium cmpds are soluble2. Nitrates, Bicarbonates, Chlorates are soluble3. Halides are soluble except Ag, Hg2

2+, Pb

4. Sulfates are soluble except Ag, Ca, Sr, Ba, Pb5. Carbonates, phosphates, chromates, sulfides are insoluble


Double Displacement (Metathesis / Exchange) Reactions

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

AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)


Ionic Equations

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

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


Molecular Equation

The molecular equation lists the reactants and products in their molecular form. This is typically NOT a good representation of what is actually happening on an atomic level.AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)


Complete Ionic / Ionic Equation• In the ionic equation all strong electrolytes

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

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

Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)

AgCl (s) + K+ (aq) + NO3- (aq)


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

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

Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)

AgCl (s) + K+(aq) + NO3-(aq)




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

Ag+(aq) + Cl-(aq) AgCl (s)




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

• 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)


Writing Net Ionic Equations1. Write a balanced molecular equation.2. Dissociate all strong electrolytes.3. Cross out anything that remains

unchanged from the left side to the right side of the equation.

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

Practice

4.3 - Acid – Base ReactionsProperties of Acids:

-Sour-Color of indicators-React with some metals (ex-Zn, Mg, Fe)-React with carbonates to form CO2

-Electrolytes

http://youtube.com/watch?v=HxiW2iPUZiw

4.3 - Acid – Base Reactions

Base Properties:-Bitter-Feel slippery-Change color of indicators-Electrolytes


Acids

• Arrhenius defined acids as substances that increase the concentration of H+ when dissolved in water.

• Brønsted and Lowry defined them as proton donors.


Acids There are only seven strong acids:• Hydrochloric (HCl)• Hydrobromic (HBr)• Hydroiodic (HI)• Nitric (HNO3)• Sulfuric (H2SO4)• Chloric (HClO3)• Perchloric (HClO4)

Weak acid examples:• Acetic• Hydrofluoric• Ammonium


Bases• Arrhenius defined bases as

substances that increase the concentration of OH− when dissolved in water.

• Brønsted and Lowry defined them as proton acceptors.


Bases

The strong bases are the soluble metal salts of hydroxide ion:• Alkali metals (Grp 1)• Calcium• Strontium• BariumWeak Base - ammonia

Bronsted Definitions

Bronsted Acid = Proton donorBronsted Base = Proton acceptor

HCl + H2O -> Cl- + H3O+

Hydronium

http://en.wikipedia.org/wiki/Hydronium

4.3 – Acid / Base

• Weak Acid = Have only partial ionization• Weak Base = Have only partial ionization

• Hydronium = H3O+

• Salt = Any ionic compound

AcidsMonoprotic – One proton

-Hydrochloric, Nitric, AceticDiprotic – Two protons

-SulfuricCan look at in two steps:


Acid-Base Reactions

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


Neutralization ReactionsGenerally, when aqueous solutions of an acid and a base are combined, the products are a salt and water.CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l)


Neutralization ReactionsWhen a strong acid reacts with a strong base, the net ionic 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)

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


Gas-Forming Reactions

• Some metathesis reactions do not give the product expected.

• In this reaction, the expected product (H2CO3) decomposes to give a gaseous product (CO2).CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)



When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water.

CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)

NaHCO3 (aq) + HBr (aq) NaBr (aq) + CO2 (g) + H2O (l)



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

SrSO3 (s) + 2 HI (aq) SrI2 (aq) + SO2 (g) + H2O (l)



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

• But just as in the previous examples, a gas is formed as a product of this reaction.

Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S (g)

4.4 Oxidation-Reduction (Redox)

• Redox Reactions• Half-Reaction• Oxidation Reaction• Reduction Reaction• Oxidation Numbers• Reducing Agent• Oxidizing Agent


Oxidation-Reduction Reactions

• An oxidation occurs when an atom or ion loses electrons.

• A reduction occurs when an atom or ion gains electrons.

• One cannot occur without the other.


4.4 – Redox ReactionsOxidation Numbers

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

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



• Nonmetals tend to have negative oxidation 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 has an oxidation number of −1.

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



• Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.Fluorine always has an oxidation number of −1.The other halogens have an oxidation number

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



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

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

Types of Redox Reactions

1. Combination-Two or more reactants from a single product-Combustion of Magnesium metal

http://www.youtube.com/watch?v=C8m6RDJvPdY

Types of Redox Reactions

2. Decomposition-Break down into 2 or more products-Decomposition of mercury (II) oxide-Elephant’s Toothpaste

Dawn detergent30% hydrogen peroxide (H202)saturated solution of potassium iodide (KI)

http://www.youtube.com/watch?v=7nxkMrmZepc

Types of Redox Reactions3. Single Displacement Reactions

-An atom or ion in a compound is displaced by anothera. -Hydrogen displacement:

-Group 1, Ca, Sr, Ba can displace from water

-Al & Fe can replace from steam-Many metals can replace from Acids

(ex – Zn)

http://youtube.com/watch?v=HxiW2iPUZiw

b. Metal Displacement-Use activity series-Elements high on

the list can remove lower elements from a compound

http://www.youtube.com/watch?v=ZKzHm12At0Q


Displacement Reactions

Metal Displacement:In this reaction, silver ions oxidize copper metal.

Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag (s)


Displacement Reactions

The reverse reaction, however, does not occur.

Cu2+ (aq) + 2 Ag (s) Cu (s) + 2 Ag+ (aq) x

c. Halogen displacementFluorine Gas > Cl > Br > Iex – Chlorine gas + Potassium

bromide

4. Disproportionation-One species is both oxidized and

reducedex – Hydrogen peroxide -> water + oxygen gas

Concentration

Molarity


Mixing a Solution• To create a solution of a

known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute.

• The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask. (best to start with some solvent in flask)


Dilution• One can also dilute a more concentrated solution

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 new flask.


4.6 - Using Molarities inStoichiometric Calculations

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

Acid Base Titration

Understand Equivalence point vs. End Point-Equivalence Pt =

-End Pt =

*Need to pick the right indicator so the Equiv Pt = the End Pt

Redox Titration

Titrate a reducing agent with an oxidizing agent

Ex: dichromate -> chromium (III) ion

Ex: permanganate -> manganese (II) ion

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AP Chapter 4 Aqueous Reactions and Solutions HW: 1 5 7 17 21 23 27 31 39 51 55 61 67 80 87 94 100 106 109