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Ions in Solution

Ions in Solution. Chapter 14. I. Ionic Compounds in Aqueous Solution (Aqueous - water is solvent) A. Theory of Ionization 1. Faraday - current causes ions to form a. Electrolytes b. Nonelctrolytes

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Ions in Solution

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  1. Ions in Solution Chapter 14

  2. I. Ionic Compounds in Aqueous Solution • (Aqueous - water is solvent) • A. Theory of Ionization • 1. Faraday - current causes ions to form • a. Electrolytes • b. Nonelctrolytes • 2. Arrhenius - ionization of molecules in water produces ions

  3. B. Dissolving Ionic Compounds • 1. The solution process for ionic compounds • a. Hydration - solution process withwater as solvent • b. Factors affect # of water molecules needed for hydration: • 1) size of ion • 2) charge of ion

  4. 2. Heat of solution for ionic compounds • heat of hydration - energy released when ions become surrounded by water • a) Exothermic - releases heat ; negative heat of solution • b) Endothermic - absorbs heat ; positive heat of solution

  5. 3. Dissociation - separation of ions when an ionic compound dissolves • NaCl ---> Na+(aq) +Cl-(aq) • 1 mol 1mol 1 mol • CaCl2 ---> Ca +2(aq) + 2Cl -(aq) • 1 mol 1mol 2 mol

  6. C. Ionic Equations and Precipitation Reactions • 1. Reactions in Solution • a. Precipitate (ppt) - insoluble substance formed through a chemical reaction in a solution • b. Some double replacement reactions produce ppt; others form a gas or water.

  7. c. Solubility Table • 1. i - insoluble - forms a ppt • 2. ss - slightly soluble - formation of a slight ppt • 3. s - soluble - no ppt forms

  8. 2. Writing Ionic Equations • a. Write formula for compound. sodium chloride = NaCl • b. Write the compound as ions: NaCl becomes Na+ + Cl- • c. Check solubility table to determine if a ppt forms • d. If all combinations give ‘s’ - reaction is NR • e. If one combination gives either ‘i’ or ‘ss’ - then a reaction takes place

  9. e. Overall ionic equation includes all ions those that form a ppt and those that are referred to as ‘spectator ions’ because they do not form a ppt • f. Net ionic equation includes only those ions that form a ppt; cancel out the spectator ions on both sides of the equation.

  10. Examples: • Write the overall ionic equation and the net ionic equation that occurs when aqueous solutions of zinc nitrate and ammonium sulfide are combined. • A solution of sodium sulfide is combined with a solution of iron(II) nitrate. Write the net ionic equation for any reaction that occurs.

  11. II. Molecular Electrolytes(Polar covalent molecules can form electrolytes) • A. The solution process for molecular electrolytes • 1. Polar molecules in water - opposite dipoles attract - if strong enough bond breaks and the molecule is separated into simpler charged parts

  12. 2. Ionization - formation of ions from solute molecules by the action of the solvent • [Dissociation: ionic compounds ---- Ionization: polar compounds]

  13. B. The Hydronium Ion • 1. H+ is only a proton, smaller than any other ion - it is attracted to others so strongly it does not have any independent existence • 2. H + + H2O ---> H3O + hydrogen ion water hydronium ion

  14. C. Strong and Weak Electrolytes • 1. Strong - 100% ions • 2. Weak - low concentration of ions

  15. III. Properties of Electrolyte Solutions • A. Conductivity of Solutions • 1. Strong-weak: degree of ionization • 2. Concentrated-dilute; amount of solute-solvent • 3. Ionization of H2O • 2H2O ---> H3O+ + OH-

  16. B. Colligative Properties of Electrolyte Solutions • 1. Electrolytes affect colligative properties more than nonelectrolytes Example: Compute the bp and fp for a solution made by adding21.6 g of NiSO4 to100 g of water.

  17. 2. Theory vs Reality • a)Theory - electrolytes reduce fp by 2,3 times - depending on # of ions • b) Reality - reduces more than nonelectrolytes , but not as much as predicted • c) Reason - because ions are attracted to each other in water - more concentrated solutions have higher attraction for each other because they are closer together

  18. 3. “Ideal Solution” - dilute enough that the ions have the expected activity

  19. IV. Colligative Properties of Solutions • A. Definition - a property that depends on the number of solute particles but is independent of their nature • 1. Nonelectrolytes - 1 solute particle • 2. Electrolytes - # of solute particlesdependent on # ions • NaCl: 2 AgNO3: 2 • MgCl2: 3 K3PO4: 4

  20. 1. Vapor Pressure Lowering - the tendency for molecules to escape from a liquid to a gas is less in a solution than a pure solvent • 2. Freezing Point Depression - solution has a lower fp than solvent ∆ tf = Kfm ∆tf- freezing point change Kf- molal freezing point constant m - molality of the solution

  21. Example: What is the fp of water in a solution of 17.12 g C12H22O11 and 200 g of water?

  22. 3. Boiling Point Elevation - solution has a higher bp than solvent ∆tb = Kbm ∆ tb - change bp Kb - molal boiling pt constant m - molality • Example: What is the bp of a solution that is made by adding 20 g C12H22O11 in 500g H20?

  23. C. Determination of Molar Mass of a Solute • 1. Determine Δtf(Δ tb) • 2. Determine m Δt = Km • 3. If ionic divide by number of particles • 4. Calculate moles of solute m X kg of solvent • 5. Molar mass = mass of solute moles of solute

  24. Example: When 1.56 g of an unknown , nonelectrolyte solute is dissolved in 200 g H2O, the ∆ tf = -0.453 Co. Determine the molar mass.

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