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Unit 2: Solids, Liquids, Equilibrium, Solubility

Unit 2: Solids, Liquids, Equilibrium, Solubility. Sam Klein Kristie Topel. General Solubility Rules. Hey, is this soluble in water?. YES. Ca(NO 3 ) 2. All nitrates are soluble!. NO. Hydroxides are insoluble except for sodium and potassium ions!. Zn(OH) 2. YES.

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Unit 2: Solids, Liquids, Equilibrium, Solubility

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  1. Unit 2: Solids, Liquids, Equilibrium, Solubility Sam Klein Kristie Topel

  2. General Solubility Rules

  3. Hey, is this soluble in water? YES Ca(NO3)2 All nitrates are soluble! NO Hydroxides are insoluble except for sodium and potassium ions! Zn(OH)2 YES Phosphates are insoluble except for sodium, potassium, and ammonium ions! K3PO4

  4. Comparative Inter/intramolecular Forces 1100 Ion-ion 700 500 Covalent bonds 100 Energy to boil (kJ/mol) (intramolecular forces) H-bonds 60 Intermolecular forces 0.1 Polar bonds Non-polar bonds

  5. A Quick Tidbit on H-Bonding • What are they? • A network between H and either N, O, or F molecules • Why so strong? • Small size of hydrogen • High electronegativity of O, N, and F

  6. General Phase Change Diagram

  7. Solid Lattice Structure

  8. Equilibrium Expression For: 3A(aq) + B(s) ↔ 2C(g) + D(l) + E(aq) ** Only gaseous and dissolved particles are expressed in the equilibrium expression because their concentrations can vary (whereas solids and liquids cannot)

  9. A Quick Review of LeChatlier's Principle If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. 3A(aq) + B(s) ↔ 2C(g) + D(l) + E(aq) If the concentration of A is raised, as the mixture returns to equilibrium a portion of all of the reactants are consumed, and as a result, the concentrations of C, D, and E will increase

  10. Practice with Equilibrium N2 + O2↔ 2NO I C E 0.25 0.25 0.0042 -x -x +2x 0.25 0.25 0.0042 + 2x Kc = 1.7 x 10-3 = (0.0042 + 2x)2 / (0.25)(0.25) Eventually… x = 0.0030 M change

  11. Precipitate Formation 25 mL of 0.1M AgNO3 solution is added to 100 mL of 0.0050M NaCl solution Would a precipitate form? AgCl(s)↔ Ag+(aq)+ Cl-(aq) [Ag+] = 0.10M(25mL/125mL) [Cl-] = 0.005M(100mL/125mL) Q = [Ag+][Cl-] Q = (0.100)(0.005) = (5.0 x 10-4) If Q<Ksp, no precipitation If Q>Ksp, precipiation Ksp = 1.8 x 10-10 Therefore Q>Ksp, and this is expected to precipitate

  12. Concentration Units Molar Concentration “molarity” M = # moles/vol. of solution Ppm (parts per million) = mass solute (in mg) / mass total (in kg) Molal Concentration “molality” m = # moles solute / mass of solvent (in kg) Mole Fractions XA = molesA/molesA + molesB +… Mass Fraction = mass solute / mass total

  13. Common Ion Effect At what concentration of OH- will one of the ions precipitate? Cd(OH)2 Ksp = 1.2 x 10-14 Ca(OH)2 Ksp = 7.9 x 10-6 (OH-) is more attracted to Cd2+, because, as the equations are similar in structure (1 cation, 2 anions) they are comparable and Cd(OH)2 would precipitate first Ca2+ Cd2+ 0.10 M Cd2+ 0.10 M Ca2+ Cd(OH)2 Cd2+(aq) + 2OH-(aq) 0.10 ~0 +x +x Ksp = 1.2*10-14 = (0.10)(x)2 X2 = 12*10-12 x = 3.5*10-6

  14. Frz Pt Depression and Boil Pt Elevation Freezing Point Depression ΔTf = iKfm Boiling Point Elevation ΔTb = iKbm i = # dissociated particles in empirical formula (Van’t Hoff factor) Kf or Kb = boiling point elevation / freezing point depression constant m = (n mol solute / mass solvent (kg))

  15. Raoult's Law Volatile Solution Pvaptotal = XAPvapA + XBPvapB +… Non-volatile Solution PvapA = XAPvapA + 0 volatile= changes to gas

  16. Henry's Law and Osmotic Pressure “the solubility of a gas is proportional to the pressure of the gas” Solg = KHenryPg Osmotic Pressure Π = (n/v)RT R = 0.082057 L · atm / K · mol C = (n / v) = (mol/L) T = temperature in Kelvin

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