unit 2 k sp and equilibrium
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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
6
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
9
Equilibrium Equations
Equilibrium Constant Equation:
Kp = Kc(RT)Δn Δn = product coeff. – reactant coeff.
10
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
11
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)
12
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)
13
Reaction Quotient
Reaction Quotient:
if Q<K, shift right
if Q>K, shift left
if Q=K, equilibrium is established
14
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
15
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
17
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
18
Common Ion EffectCommon ions in a solution suppress the reactant’s solubility and push the equilibrium to the left.
19
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
20
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
21
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)
23
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
24
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
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