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Solutions, Solubility,and Reaction Types

Brown, LeMay Ch 4AP Chemistry

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4.1: Solutions & Expressing ConcentrationSolution: homogeneous mixture of 2 or more

substancessolute: component present in lesser quantitysolvent: component present in greater quantity

Molarity (M) = moles solute =mol

volume of solution L

Molality (m) = moles solute =mol

kg of solvent kg

*Normality (N): associated with acid & base strength. Normality = molarity x n (where n = the number of protons exchanged in a reaction). = (moles solute)(# of acid/base equivalents) = mol

volume of solutionL

Mole Fraction

XA= nA/ total moles

Practice Problem

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Titration- moles of acid= moles of base @ the end point-use stoichiometry to find other reactant/product molesM1V1= M2 V2 (sometimes used to get moles , M= moles/L , so moles= M XV)-What other ways can you get the moles- for a solid? For a gas?-color change by indicator indicates end point-end point and equivalence points should be close

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Dilution: (Minitial)(Vinitial) = (Mfinal)(Vfinal)

Ex: How much water must be added to a solution that contains 100.0 g NaOH in 500. mL of solution to make the final concentration 2.00 M?

Minitial = (100.0 g NaOH)/(40.00 g/mol NaOH) = 5.00 M

0.500 L

(Mi)(Vi) = (Mf)(Vf) = (5.00 M)(0.500 L) = (2.00 M)(Vf)

Vf = 1.25 L, so 0.75 L water must be added.

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4.2: Properties of SolutesIonic compounds (salts): dissociate in water by solvation, in which polar H2O molecules surround

and separate ions from ionic crystal lattice

Molecular compounds: do not ionize because intramolecular bonds are stronger than bonds that form between H2O and molecule

Acids and bases, sometimes considered molecular (depending on strength), may also ionize.

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Electrolyte: substance which, in aqueous solution, ionizes and thus conducts electricity. Ex: salt in water.http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html (salt dissolving in water)

Non-electrolyte: substance which, in aqueous solution, does not dissociate and thus does not conduct electricity

Strong & weak electrolytes: conductivity depends on degree of dissociation and equilibrium position: HA (aq) ↔ H+ (aq) + A- (aq)

Strong = nearly completely dissociatedWeak = partially dissociated

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%25::100%25::/sites/dl/free/0072512644/117354/07_Strong_Weak_Nonelectrolytes.swf::Strong

%20Electrolytes,%20Weak%20Electrolytes,%20and%20Nonelectrolytes ( electrolytes animation)

http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/electroChem/conductivity.html (Conductivity of different substances)

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4.3: Acids & BasesBronsted-Lowry definitions:

Acids: H+ donorBases: H+ acceptor

Figure 1: Strong & weak: depends on degree of dissociation (Ka value, Table 4.1, p. 117)

Strong Acids Strong Bases

HBr, HCl, HI

HNO3, H2SO4

HClO4, HClO3

Group 1A’s: LiOH, NaOH, KOH, RbOH,

CsOH

Heavy 2A’s: Ca(OH)2, Sr(OH)2,

Ba(OH)2

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4.4: Ionic Equations1. Molecular equation: shows complete chemical equation

with states of matter, undissociated

BaCl2 (aq) + Na2SO4 (aq) → 2 NaCl (aq) + BaSO4 (s)

2. Complete ionic equation: shows complete chemical equation with states of matter, dissociated if appropriateBa2+(aq) + 2 Cl-(aq) + 2 Na+(aq) + SO4

2-(aq) →2 Cl-(aq) + 2 Na+(aq) + BaSO4 (s)

Spectator ions: present in reaction but do not “participate”; depend on solubility rulesCl- (aq) and Na+ (aq)

http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf ( Precipitation Animation)

3. Net ionic equation: shows chemical equation without spectator ionsBa2+ (aq) + SO4

2- (aq) → BaSO4 (s)

Solubility Rules (memorize them!)Figure 2: Compounds that are always soluble.

Compounds containing…

Important Exceptions

NO3-

CH3COO-

Cl-, Br-, I-

SO42-

None

None

Ag+, Hg22+, Pb2+

Hg22+, Pb2+,

Sr2+, Ba2+, Ca2+

• Also, compounds with Group 1A and NH4+ cations

Figure 3: Compounds that always insoluble.

Compounds containing…

Important Exceptions

• Other anions (e.g., BrO3- or Cr2O7

2-) are generally insoluble except with the soluble cations (Group 1A and NH4

+)• http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH2904

CO32-, CrO4

2-, C2O42-

PO43-

S2-, O2-, OH-

Alkali metals, NH4+

Alkali metals, NH4+,

Sr2+, Ba2+, Ca2+

http://core.ecu.edu/chem/chemlab/exper4/procedures.htm

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AP Exam: Predicting Reaction ProductsReactants:1. Write all soluble ionic compounds, strong

acids, and strong bases in aqueous solution as their constituent ions. Never write NaCl or Ca(NO3)2, HCl or HNO3, NaOH or Ba(OH)2, etc.

Products:1. Assume a reaction occurs.2. Inspect all of the ions to see if any

precipitates will form.3. Cross out any spectator ions.4. Balance the reaction (and states of matter

are not needed.)

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Practice Predicting Precipitation Reactions

Observations from previous AP exams:These types of reactions generally involve mixing two solutions, but may include the addition of hydrogen sulfide or hydrogen chloride gas.Many involve formation of a single insoluble precipitate, but watch for the possibility of two insoluble products.

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ExamplesA. Dilute hydrochloric acid is added to a dilute

solution of mercury (I) nitrate.

B. Dilute sulfuric acid is added to a solution of barium chloride.

H+ + Cl- + Hg22+ + NO3

-→ Hg2Cl2 + NO3- + H+

H+ + SO42- + Ba2+ + Cl- → BaSO4

+ H+ + Cl-

2 Cl- + Hg22+ → Hg2Cl2

SO42- + Ba2+ → BaSO4

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C. Hydrogen sulfide gas is added to a solution of cadmium nitrate.

D. A scoop of silver nitrate is added to a solution of sodium chromate.

H2S + Cd2+ + NO3- → CdS + H+ + NO3

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AgNO3 + Na+ + CrO4

2- → Ag2CrO4 + Na+ + NO3-

2 AgNO3 + CrO4

2- → Ag2CrO4 + 2 NO3-

H2S + Cd2+ → CdS + 2 H+

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Other reactions to know:Acid + Base → Salt + WaterEx: A solution of cesium hydroxide is added to a solution of nitric acid.

Nonmetal oxide + Water → OxyacidTherefore, nonmetal oxides are called acid anhydrides.

Ex: Sulfur trioxide gas is added to excess water.

Metal oxide + Water → BaseTherefore, metal oxides are called basic anhydrides.

Ex: Solid sodium oxide is added to water.

Cs+ + OH- + H+ + NO3- → Cs+ + NO3

- + H2O

H+ + OH- → H2O

SO3 + H2O → H2SO4

SO3 + H2O → 2 H+ + SO42-

Na2O + H2O → NaOH

Na2O + H2O → 2 Na+ + 2 OH-

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Nonmetal oxide + Metal oxide → SaltEx: Solid calcium oxide is heated in the presence of sulfur trioxide gas.

CaO + SO3 → CaSO4

If this were in water:CaO + H2O → Ca2+ + OH-

andSO3 + H2O → H2SO4 → H+ + SO4

2-

So, our overall reaction would be:Ca2+ + H2O + SO4

2- → CaSO4 + H2O

But this can happen without water:CaO + SO3 → CaSO4

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Metal oxide + Acid → Salt + WaterEx: Potassium oxide solid is added a solution of hydrochloric acid.

Nonmetal oxide + Base → Salt + WaterEx: Carbon dioxide is bubbled through a solution of barium hydroxide.

K2O + H+ + Cl- → K+ + Cl- + H2O

(K+ + O2-) + H+ + Cl- → K+ + Cl- + H2O

K2O + 2 H+ → 2 K+ + H2O

CO2 + Ba2+ + OH- → BaCO3 + H2O

CO2 + Ba2+ + 2 OH- → BaCO3 + H2O

Ion (aq)Co2+

[CoCl4]2-

RoseBlue

Cr3+

CrO42-

Cr2O72-

GreenYellowOrange

Cu2+

[Cu(NH3)4]2+

Light blueMedium blue

Fe2+

Fe3+

[Fe(SCN)]2+

GreenYellow-brown

Red

Mn2+ Pink

Ni2+ Green

Grp I-A+

Grp II-A2+

Al3+

Colorless

Zn2+ Colorless or “milky”

Compounds ColorPbI2

Grp I-A+/II-A2+ & CrO42-

Yellow

Grp I-A+/II-A2+ & Cr2O72- Orange

AgXGrp I-A+/II-A2+ & NO3

-, C2H3O2

-, X-, SO42-

White

AgNO3White, turns

black in sunlight

CuO Green

Fe2O3 Rust

KMnO4 Purple

HgO Dark red

NO2 (g) Brown

Any suggestions for others you’ve seen on old/practice exams, let me know.