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Chapter 13 Ions in Aqueous Solutions and Colligative Properties

Chapter 13 Ions in Aqueous Solutions and Colligative Properties. 13-1 Compounds in Aqueous Solutions. Solid compounds can be…. IONIC. MOLECULAR. molecules composed of covalently bonded atoms atoms held together by noncovalent IMF. crystal structure is made up of charged particles

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Chapter 13 Ions in Aqueous Solutions and Colligative Properties

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  1. Chapter 13 Ions in Aqueous Solutions and Colligative Properties 13-1 Compounds in Aqueous Solutions

  2. Solid compounds can be… IONIC MOLECULAR molecules composed of covalently bonded atoms atoms held together by noncovalent IMF • crystal structure is made up of charged particles • ions held together by ionic attractions When they dissolve in water, ionic and molecular compounds behave differently.

  3. The separation of ions that occurs when an ionic compound dissolves Dissociation • One formula unit of NaCl produces two ions: • One mole of NaCl produces two moles of ions 1 mol of Na+ and 1 mol of Cl- • One formula unit of CaCl2 produces three ions: • One mole of CaCl2 produces three moles of ions 1 mol Ca2+ and 2 mol of Cl-

  4. Dissociation Equations NaCl(s)  Na+(aq) + Cl-(aq) AgNO3(s)  Ag+(aq) + NO3-(aq) MgCl2(s)  Mg2+(aq) + 2 Cl-(aq) Na2SO4(s)  2 Na+(aq) + SO42-(aq) AlCl3(s)  Al3+(aq) + 3 Cl-(aq)

  5. Sample Problem Write the equation for the dissolution of aluminum sulfate Al2(SO4)3 in water. How many mole of Al ions and sulfate ions are produced?

  6. Precipitation Reactions Solubility Rules • No compound is completely insoluble • Compounds of very low solubility can be considered insoluble • Dissociation equations cannot be written for insoluble compounds

  7. Predict the products… Ammonium sulfide and cadmium nitrate

  8. Double replacement forming a precipitate… Double replacement (ionic) equation Pb(NO3)2 (aq) + 2KI (aq)  PbI2 (s) + 2KNO3 (aq) Spectator ions are those ions that do not take part in a chemical rxn and are found in solution both before and after the rxn Complete ionic equation shows compounds as aqueous ions Pb2+ (aq) + 2 NO3- (aq) + 2 K+ (aq) +2 I- (aq)  PbI2 (s) + 2 K+ (aq) + 2 NO3- (aq) Net ionic equation eliminates the spectator ions Pb2+ (aq) + 2 I- (aq)  PbI2 (s) Includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution

  9. ID the precipitate that forms when aqueous solutions of zinc nitrate and ammonium sulfide are combined. • a. Write out the equation for the possible double replacement reaction • b. Write the overall ionic equation. Circle spectator ions. • c. Write the net ionic equation.

  10. Will a precipitate form if solutions of potassium sulfate and barium nitrate are combined? Write the net ionic equation for the reaction:

  11. Ionization • def. Ions are formed from solute molecules by the action of the solvent • Polar water molecules are attracted to polar solute molecules • Electronegative oxygen of water is attracted to electropositive portion of a solute molecule • Electropositive hydrogen of water is attracted to the electronegative portion of a solute molecule • The extent to which a solute ionizes in solution depends on the strength of the bonds within the molecules of the solute and the strength of the attraction between the solute and solvent.

  12. The Hydronium Ion • Many molecular compounds contain a H atom bonded by a polar covalent bond many ionize in water to release H+ ions • When H+ attracts to water and formsH3O+ is called the "hydronium" ion

  13. Strong Electrolytes • Any compound of which all or almost all of the dissolved compound exists as ions in an aqueous solution • Hydrogen halides: HCl, HBr, HI (100% ionized in solution)

  14. Weak Electrolytes • A compound of which a relatively small amount of the dissolved compound exists as ions in an aqueous solution • Examples: HF, organic acids (acetic acid) http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/0072512644/117354/07_Strong_Weak_Nonelectrolytes.swf::Strong%20Electrolytes,%20Weak%20Electrolytes,%20and%20Nonelectrolytes

  15. Chapter 13 Ions in Aqueous Solutions and Colligative Properties 13-2 Colligative Properties

  16. Colligative Properties • All solutes affect the physical properties of a solution by the concentration of solute particles, not by the chemical nature of the particles. • Calculations involving CP [ ] is in molality (m)

  17. Vapor Pressure Lowering Effect of Solutes on Vapor-Pressure- Any nonvolatile solute will lower the vapor pressure of a solution, having two noticeable effects: • Raising the boiling point of the solution • Lowering the freezing point of the solution

  18. Solute particles take up space @ the liquid-air surface. So vapor pressure is lowered, boiling occurs at a higher temp b/c more energy is required for the vapor pressure to equal the atmospheric pressure.

  19. Freezing Point Depression • Solutions have lower freezing points than pure solvents. • If the solution is aqueous, its freezing point will always be lower than 0C. • Q. How much lower? • A. Depends on the # & concentration of solute particles.

  20. Colligative Properties • Colligative properties depend on: number & concentration of solute particles • Since ionic substances dissolve into multiple particles, their colligative effects are greater than those of covalent substances.

  21. Freezing Point Depression • Ionic solutes depress the freezing point more than covalent solutes. Look at their solubility rxns, note the number of particles formed: • Ionic: NaCl (s) + H2O (l)  Na+ (aq) + Cl- (aq) • Covalent: C6H12O6 (s) + H2O (l)  C6H12O6 (aq) 2 particles formed 1 particle formed

  22. Molal Freezing-Point Constant for Water • The freezing-point depression of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute Kf= -1.86 °C/m • Freezing-Point Depression • The difference between the freezing points of the pure solvent and a solution of a nonelectrolyte in that solvent Δtf = Kfm Where: m = molality Δtf = change in freezing point

  23. Animal Antifreeze  animals living in cold climates have own kind of anitfreeze • Caribou  substances in lower leg that prevent freezing = able to stand in snow for long periods of time without freezing • Fish natural chemicals antifreeze called glycoprotein which prevents ice crystals from forming in moist tissues

  24. Boiling Point Elevation • Solutions have higher boiling points than pure solvents. • If the solution is aqueous, its boiling point will always be higher than 100C. • Boiling: Temperature at which vapor pressure equals atmospheric pressure.

  25. Molal Boiling-Point Constant for Water • The boiling point elevation of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute Kb= 0.51 °C/m • Boiling-Point Elevation • The difference between the boiling points of the pure solvent and a solution of a nonelectrolyte in that solvent Δtb = Kbm Where: m = molality Δtb = change in boiling point

  26. The van’t Hoff Factor, i Electrolytes may have two, three or more times the effect on boiling point and freezing point, depending on its dissociation. T = i  K m

  27. Freezing Point Depression and Boiling Point Elevation Constants

  28. Dissociation Equations i = 2 NaCl(s)  Na+(aq) + Cl-(aq) i = 2 AgNO3(s)  Ag+(aq) + NO3-(aq) i = 3 MgCl2(s)  Mg2+(aq) + 2 Cl-(aq) i = 3 Na2SO4(s)  2 Na+(aq) + SO42-(aq) AlCl3(s)  Al3+(aq) + 3 Cl-(aq) i = 4

  29. Van’t Hoff factor

  30. 1.65 g of sodium chloride is added to 220.0 kg of water at 34 °C. How will this affect the boiling point of the water?

  31. What is the freezing point of a solution prepared by adding 140. g trichothecin (C19H24O5) to 0.746 kg of benzene? The freezing point of pure benzene is 5.5 °C. The freezing point constant for benzene is 5.12 °C/m.

  32. What is the new boiling point of a solution prepared by adding 96.0 g of sodium acetate to 383 mL of water? The boiling point constant for water is 0.52 °C/m.

  33. What is the freezing point depression when 309 g of isoprene (C5H8) is dissolved in 747 g of ethyl ether? The freezing point constant for ethyl ether is 1.79 °C/m.

  34. HOMEWORK pg 450 #1-3 pg 451 #1-3

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