Unit 2 K sp and Equilibrium By: Michael Nolan Kristi Rice Erika Baucom

Important Equations

Bonds Van der Waals London Dispersion Dipole-Dipole Hydrogen Bonds (N,O,F)

Solids Crystalline vs. amorphous Crystalline- ionic and network (diamond) Amorphous- glass and rubber Unit Cell Simple 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-centeredFace-centered

6 Sodium Chloride has a face-centered crystal structure. How many Cl – ions and how many Na + ions? Also, what is the empirical formula? MgO has the same crystal structure and a density of 3.58 g/cm 3. What is the length of one edge? Example

Solubility The amount of the substance that can be dissolved in a given quantity of solvent at a given temperature Soluble 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: K p = K c (RT) Δn Δn = product coeff. – reactant coeff.

10 K sp and Solubility K sp is equilibrium constant for dissolved ionic substances Solubility is affected by: Henry’s law S g = k H P g 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 Types Molecular Equation: Pb(NO 3 ) 2 (aq) + 2KI (aq) → PbI 2 (s) + 2KNO 3 (aq) Complete Ionic Equation: Pb 2+ (aq) + 2NO 3 – (aq) + 2K + (aq) + 2I – → PbI 2 (s) + 2K + (aq) + 2NO 3 – (aq) Net Ionic Equation: Pb 2+ (aq) + 2I – (aq) → PbI 2 (s)

12 Basic Solubility Terms Dilute - 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 AgIO 3 (K sp = 3.1 x 10 –8 ) precipitate when 20 mL of 0.10 M AgNO 3 is mixed with 10 mL of M NaIO 3 ? Suppose a solution contains 0.10 M Ca(NO 3 ) 2 and 0.10 M Ba(NO 3 ) 2.The cations are to be separated by adding NaF to form CaF 2 (K sp =3.9 x 10 –11 ) and BaF 2 (K sp =1.7 x 10 –6 ). Which precipitate will form first? What would be the F – concentration at that point? Example

15 Le Châtlier’s Principle If 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 Calculations Molarity = moles = M L Molality = moles solute = m kg solvent Mass percentage = mass component x 100% total mass ppm: ______ x 10 ⁶ 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 g/cm 3. Calculate the mass percent and molal concentration of alcohol. Example

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

19 Complex Ion Formation A complex ion is the assembly of a metal ion and the lewis bases bonded to it. K f is the equilibrium constant of its formation with the hydrated metal ion. Example: Fe CN – → [Fe(CN) 6 ] 4– K f = 7.7 x K net = K sp x K f

20 FeCO 3 has K sp = 3.5 x 10 –11. [Fe(CN) 6 ] 4– has a K f = 7.7 x a.) Combine 2 reaction equations to form a net reaction describing a system in which concentrated KCN is added to an excess of solid FeCO 3 in H 2 O. b.) Calculate K net and write a general expression for it. c.) Calculate the theoretical solubility of FeCO 3 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 P vap =P atm 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: ΔT b = ik b c molal Freezing Point Depression: ΔT f = ik f c molal Osmotic Pressure - pressure required to prevent osmosis by pure solvent toward the solution with the higher solute concentration ∏ = c molar RT i - Van’t Hoff Factor; number of products solute dissociates into (“ideally”; “real” Van’t Hoff factor is lower)

22 B.P. Elevation and F.P. Depression Boiling 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 P vap to equal P atm 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) ( content/uploads/2010/08/sad-smiley.jpg) content/uploads/2010/08/sad-smiley.jpg

23 A polyprotic acid w/ molar mass of g/mol is dissolved in H 2 O. Suppose 74.3 g of the acid is dissolved in 250. g H 2 O, and the resulting solution is heated to its boiling point. H 2 O’s b.p. elevation constant, k b, 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; ) 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 critical point supercritical fluid