Unit 2Unit 2KKspsp and Equilibrium and Equilibrium

By: Michael NolanKristi Rice

Erika Baucom

Important Equations

BondsVan der Waals

London DispersionDipole-Dipole

Hydrogen Bonds (N,O,F)

SolidsCrystalline vs. amorphous

Crystalline- ionic and network (diamond)Amorphous- glass and rubber

Unit CellSimple Cubic- just corners (1/8), one atom

Body-centered- corners and middle (1), two atoms

Face-centered- corners and faces (1/2), four atoms

Crystalline Structures

(Prentice Hall Student Component CD)

Simple cubic

Body-centered Face-centered

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Sodium Chloride has a face-centered crystal structure. How many Cl– ionsand how many Na+ ions? Also,what is the empirical formula?

MgO has the same crystalstructure and a density of 3.58 g/cm3. What is the length of one edge?

Example

SolubilityThe amount of the substance that can be dissolved in a given quantity of solvent at a given temperatureSoluble solution: clear solution, light passes straight through b/c particles are about same size as light waves

Insoluble solution: cloudy solution, light path is scattered b/c particles larger than light waves

Solubility (continued)Saturated: solution is in equilibrium with undissolved solute so additional solute won’t dissolve

Solubility vs. temp. graphs for gases and solids on the board

Unsaturated: can dissolve more solute

Supersaturated: contains more solute than needed to form a saturated solution; unstable; agitation can spur precipitates

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Equilibrium Equations

Equilibrium Constant Equation:

Kp = Kc(RT)Δn Δn = product coeff. – reactant coeff.

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Ksp and Solubility Ksp is equilibrium constant for dissolved ionic substances

Solubility is affected by: Henry’s law

Sg = kHPg

Solubility of a gas is directly proportional to partial pressure

Temperature Inversely proportional with gas solubility Directly proportional with solid solubility

Surface Area Polarity of solvent vs. solute; like dissolves like pH - Example: basic anions are more easily dissolved in acidic solutions

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Reaction Equation TypesMolecular Equation:Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)

Complete Ionic Equation:Pb2+ (aq) + 2NO3

– (aq) + 2K+ (aq) + 2I– → PbI2 (s) + 2K+ (aq) + 2NO3–

(aq)

Net Ionic Equation:Pb2+ (aq) + 2I– (aq) → PbI2 (s)

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Basic Solubility TermsDilute - to lower a concentration by adding water

Miscibility - the amount of liquid that can be dissolved in another liquid; “dissolvability” of liquids

Saturated - solution is in equilibrium with undissolved solute so added solute will not dissolve

Equilibrium - when opposing reactions proceed at equal rates and have constant concentrations (“Dynamic” Equilibrium)

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Reaction Quotient

Reaction Quotient:

if Q<K, shift right

if Q>K, shift left

if Q=K, equilibrium is established

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Will AgIO3 (Ksp = 3.1 x 10–8) precipitate when 20 mL of 0.10 M AgNO3 is mixed with 10 mL of 0.015 M NaIO3?

Suppose a solution contains 0.10 M Ca(NO3)2 and 0.10 M Ba(NO3)2.The cations are to be separated by adding NaF to form CaF2 (Ksp=3.9 x 10–11) and BaF2 (Ksp=1.7 x 10–6). Which precipitate will form first? What would be the F– concentration at that point?

Example

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Le Châtlier’s PrincipleIf a system at equilibrium is disturbed by a change, the system will shift its equilibrium position to counteract the effect of the disturbance

Examples:

Increase Temperature: shift to reaction with +ΔH

Decrease Temperature: shift to reaction with –ΔH

Increase Pressure/Decrease Volume: shift to side with fewer moles of gas to decrease pressure

Add Catalyst: No Shift, catalyst increases both forward and reverse reaction rates

Solubility and Equilibrium CalculationsMolarity = moles = M L

Molality = moles solute = m kg solvent

Mass percentage = mass component x 100% total massppm: ______ x 10⁶

Volume fraction = V solute V total

Mole fraction = X = moles component moles total

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Wine contains 12.5% ethanol by volume. It’s density is 0.789 g/cm3. Calculate the mass percent and molal concentration of alcohol.

Example

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Common Ion EffectCommon ions in a solution suppress the reactant’s solubility and push the equilibrium to the left.

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Complex Ion FormationA complex ion is the assembly of a metal ion and the lewis bases bonded to it.

Kf is the equilibrium constant of its formation with the hydrated metal ion.

Example: Fe2+ + 6CN– → [Fe(CN)6]4–

Kf = 7.7 x 1036

Knet = Ksp x Kf

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FeCO3 has Ksp = 3.5 x 10–11. [Fe(CN)6]4– has a Kf = 7.7 x 1036.

a.) Combine 2 reaction equations to form a net reaction describing a system in which concentrated KCN is added to an excess of solid FeCO3 in H2O.b.) Calculate Knet and write a general expression for it.c.) Calculate the theoretical solubility of FeCO3 in 2.50 M KCN.

Example

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Phase Changes Vocabulary Vapor Pressure - pressure of a vapor in contact with its liquid

or solid form; boiling point is when Pvap=Patm

Volatile - evaporates readily Phase Diagrams - pressure vs. temperature graphs that show

where the states of matter exist at equilibrium Colligative Properties - depend on the quantity or

concentration, but not the identity, of solute particles Boiling Point Elevation: ΔTb = ikbcmolal

Freezing Point Depression: ΔTf = ikfcmolal

Osmotic Pressure - pressure required to prevent osmosis by pure solvent toward the solution with the higher solute concentration ∏ = cmolarRT

i - Van’t Hoff Factor; number of products solute dissociates into (“ideally”; “real” Van’t Hoff factor is lower)

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B.P. Elevation and F.P. DepressionBoiling Point Elevation - the ions dissolved in a solvent hinder the solvent molecules from vaporizing; lowers the solvent’s vapor pressure, so more heat is necessary for Pvap to equal Patm and boil

Freezing Point Depression - the ions dissolved in a solvent physically hinder the solvent’s molecules from creating an orderly crystalline arrangement

(StickerGiant.com)

(http://www.avromysegalonline.com/wp-content/uploads/2010/08/sad-smiley.jpg)

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A polyprotic acid w/ molar mass of 103.2 g/mol is dissolved in H2O. Suppose 74.3 g of the acid is dissolved in 250. g H2O, and the resulting solution is heated to its boiling point. H2O’s b.p. elevation constant, kb, is 0.512°C-kg/mol. If the first proton dissociates 100% and the remaining protons don’t dissociate, what is the boiling point of the solution?

Example

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Phase Diagrams

(Science Fair Projects Encyclopedia;http://www.all-science-fair-projects.com/science_fair_projects_encyclopedia/Phase_(matter

) )

Triple Point - at which all three phases are in equilibrium

Critical Point - Critical Temperature and Critical Pressure Critical Temperature -

highest temperature at which there is a distinct liquid phase

Critical Temperature - pressure required to condense substance at critical temp.

Supercritical Fluid - indistinguishable liquid/gas phase

criticalpoint

supercritical

fluid