1 Solutions, Solubility, and Reaction Types Brown, LeMay Ch 4 AP Chemistry.
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Transcript of 1 Solutions, Solubility, and Reaction Types Brown, LeMay Ch 4 AP Chemistry.
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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
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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)
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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
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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
-
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
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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”
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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.