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Additional Aspects of Aqueous Equilibria Part 1

Additional Aspects of Aqueous Equilibria Part 1. Splash. Ch. 17 in Textbook. I) The Common-Ion Effect A) What is it?. Man, now I’m all wet. Given: a weak acid solution Added: a salt of the acid

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Additional Aspects of Aqueous Equilibria Part 1

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  1. Additional Aspects of Aqueous EquilibriaPart 1 Splash. Ch. 17 in Textbook

  2. I) The Common-Ion Effect A) What is it? Man, now I’m all wet. • Given: a weak acid solution • Added: a salt of the acid • Because the salt will ionize completely (strong electrolyte), you are adding the conjugate base • The presence of this common ion is a stress to the equilibrium of the weak acid • The equilibrium will then shift towards the molecular form of the weak acid and thus _____________ its solubility • The pH thus ______________ HW: 17.2

  3. B) Acid Example • Ex 1) What is the pH of a solution consisting of 0.30 M acetic acid and 0.30 M sodium acetate? (Ka = 1.8 x 10-5) I just released my smash debut album, “The Sounds of Nature: Crashing Waves.”

  4. C) Base Example • Ex 2) 5.60 g of solid NH4Cl are added to a 2.0 M solution of NH3 with a total volume of 100.0 mL. What is the pH if the Kb value for ammonia is 1.8 x 10-5? These seagulls are driving me nuts, I tell ya! HW: 17.4 (a) – (c), 17.6 (use Appendix D), 17.8

  5. II) Buffered SolutionsA) What are they? This surfer dude’s goin’ down…LIKE TOTALLY! • Can resist changes in pH (like blood) • Based on common ion effect • Contain both an acid to neutralize base added and a base to neutralize acid added • Prepared by pairing a weak acid/weak base with its conjugate salt • Most effective when the concentration of the weak acid/weak base is equal to that of its conjugate salt • Link • Link

  6. Oooh…mermaids. Hey, ladies! Oh, wait that was a manatee. Ugh! I ALWAYS DO THAT! B) Buffer Capacity • Buffer Capacity: the degree to which a buffer can resist changes in pH; the amount of acid or base that can be added to a buffer before a significant pH change occurs • Depends on the concentrations of weak acid/weak base and conjugate salt

  7. C) Calculating pH for Buffers • Using an ICE chart is the LONG way; however, there is a shortcut… • Henderson-Hasselbalch Equation: used to calculate the pH of a buffer • pH = pKa + log [base] [acid] • pOH = pKb + log [acid] [base] Don’t pretend like I don’t see you getting into that lifeboat, captain! What happened to going down with your ship!?

  8. Ex 3) What is the pH of a buffer that is 0.12 M lactic acid, HC3H5O3, and 0.10 M sodium lactate? (Ka = 1.4 x 10-4) Mommy, does water REALLY go to live in the clouds when it evaporates? HW: 17.12, 17.14

  9. D) Addition of Strong Acids or Bases to Buffers • If a strong acid or base is added to the buffer, we want to see how the pH is (slightly) changed. • Write the neutralization equation, do an ICE chart to find the new equilibrium concentrations, then apply the H-H equation… Don’t you just love the word “buoy?” Say it. It’s fun! Buoy…booey… boooooey…

  10. Ex 4) A buffer consisting of 0.300 M acetic acid and 0.300 M sodium acetate has a pH of 4.74. After the addition of 0.020 M NaOH (assume no volume changes), what is the new pH? “Don't go chasing waterfalls. Please stick to the rivers and the lakes that you're used to…”

  11. Ex 5) A buffer consisting of 0.300 M acetic acid and 0.300 M sodium acetate has a pH of 4.74. After the addition of 0.020 M HCl (assume no volume changes), what is the new pH? This coastline is so ugly. I think I feel a SCHUNAMI coming on! HW: 17.18

  12. Amazing…so much water and yet you’d die of thirst if you kept drinking me! III) Acid-Base Titrations A) What are they? • A known concentration of acid (or base) is added to a basic (or acidic solution) of unknown concentration • Equivalence Point: the point at which stoichiometrically equal amounts of acid and base have reacted with one another • End Point: where indicator color change occurs (usually before or after equivalence point, depending on where the indicator changes color)

  13. So seriously, be honest, am I blue or green? Clear? I’m colorblind, so I’m never sure. • A pH titration curve shows the pH as a function of the volume of titrant added • Link • Allows us to determine the equivalence point which is not always a pH of 7! Dspace.mit.edu

  14. B) Strong Base added to Strong Acid I taste salty for some reason… • A: pH found from initial concentration of acid • B: pH found from concentration of acid that hasn’t been neutralized • C: pH= 7.00 • D: pH found from excess base D C B A Chembio.uoguelph.ca

  15. Ex 6) Calculate the pH when the following quantities of 0.100 M NaOH solution have been added to 50.00 mL of 0.100 M HCl solution: • (a) 49.00 mL Ironically, I absolutely HATE the Beach Boys.

  16. I don’t swim in your toilet, so don’t pee in me! • (b) 51.00 mL HW: 17.28

  17. Oh, it’s Shark Week again? I almost forgot! Seems like just yesterday that someone got devoured… • Notice how rapidly the pH rises close to the equivalence point (even the addition of a single drop of base can cause a change of more than one pH unit) • An indicator such as methyl red can be used to change from yellow to red from pH 4.2-6.0 (an endpoint that occurs before the equivalence point) • An indicator such as phenolphthalein can be used to change from colorless to pink from pH 8.3 -10 (an endpoint that occurs after the equivalence point) D C B A Chembio.uoguelph.ca

  18. You’d think by now I’d be used to the sight of a dead fish, but it still creeps me out. It just floats there…gross! Physchem.co.za

  19. C) Strong Base added to Weak Acid Hey! Hi! Shoot, I don’t think she saw me wave… • A: pH found from ICE chart, Ka expression, and solving for [H+] • B (buffering region): pH found by doing ICE chart for initial neutralization, then applying Henderson-Hasselbalch for remaining weak acid • C: pH≠7! pH found by assuming all base reacted, then writing Kb expression for conjugate base of weak acid, solving for [OH-], pOH, then finally pH • D: pH found from excess base • Link D C B A Dspace.mit.edu

  20. Ex 7) (a) Calculate the pH of the solution formed when 45.0 mL of 0.100 M NaOH is added to 50.0 mL of 0.100 M HC2H3O2. (Ka = 1.8 x 10-5) Moby Dick…yeah, I met him once. Total jerk.

  21. (b) Calculate the pH at the equivalence point in the titration of 50.0 mL of 0.100 M HC2H3O2 with 0.100 M NaOH. Seriously, bro, a jet ski? Do you think that makes you look tough or something? HW: 17.22, 17.24, 17.29

  22. D) Relationship between Ka and the Shape of the Titration Curve The scuba diving is great this time of year…just ask your local scuba diving expert, James Burchalewski! Library.tedankara.k12.tr

  23. Whoa, look at the time. Time for some low tide action. See you suckas later! E) Polyprotic Acids • Have multiple equivalence points due to multiple neutralization reactions Bio.cmu.edu

  24. Additional Aspects of Aqueous Equilibria Part 2 Chapter 17 in Textbook Zazzle.com

  25. IV) Solubility Equilibria:A) What are they? • Heterogeneous equilibria between dissolving and precipitation (a saturated solution) • A quantitative means of determining how soluble a solid is in water • Not always as simple as soluble or insoluble like in net ionic equations Www2.ucdsb.on.ca

  26. B) Ksp • The equilibrium constant for the dissolving of a solid is designated Ksp for solubility-product • Ksp remains constant at a given temperature • The solid dissolving never appears in the equilibrium expression and is NOT affected by Le Chatelier’s Principle since it is pure • Link Genchem.rutgers.edu

  27. Ex 8) Write the Ksp expression for a saturated solution of CaF2(s). Allaboutfrogs.org

  28. C) Ksp and solubility • If a question asks for the molar solubility, then we can solve for the concentration in M using the equilibrium expression Commons.wikipedia.org

  29. Ex 9) If the Ksp for CaF2 is 3.9 x 10-11, what is its molar solubility? Roflzoo.com HW: 17.34, 17.38, 17.40

  30. V) Factors that Affect Solubility:A) Common-Ion Effect • Adding a common ion to a solution equilibrium decreases the solubility according to Le Chatelier’s • Link Greenfroginternet.com

  31. B) pH • As the pH decreases, the solubilities of metal hydroxides increases; think of the increasing H+ as reacting and removing the OH-, thus shifting the equilibrium to the right (towards the ions) • This rule also applies to anions that are weak bases: F-, CO3-2, PO4-3, CN-, or S-2 • Link Micropig.tumblr.com

  32. C) Complex Ions • When a metal ion acts as a Lewis acid, it accepts electrons from a Lewis base; this often results in the formation of a complex ion • Given equilibrium constant Kf: the greater the formation constant, the more stable the complex ion and the more soluble the metal • Rule of thumb: solubility of metal salts increase in the presence of NH3, CN-, and OH- (ligands) due to the formation of complex ions Studiotota.com

  33. Ex 10) The Ksp for AgCl is 1.8 x 10-10, but adding ammonia greatly increases the solubility. Why? Woodka.com

  34. Ex 11) Write the Kf for the complexation of silver ion with ammonia. Midnightparking.com

  35. D) Amphoterism • Al+3, Cr+3, Zn+2, Sn+2 when combined with OH- or O-2 are not just soluble in acidic solutions, but also basic ones; they are thus amphoteric • This is a result of complexes formed in water • Ex) Al(OH)3(s) + OH- ↔ Al(OH)4-(aq) Evilscience.co.uk

  36. VI) Precipitation and Separation of Ions • Given the following: • BaSO4(s) ↔ Ba+2(aq) + SO4-2(aq) • At any given time, Q = [Ba+2][SO4-2] • If Q > Ksp, precipitation occurs until Q = Ksp • If Q = Ksp, equilibrium exists • If Q < Ksp, solid dissolves until Q = Ksp Blog.greens.org.nz

  37. Ex 12) Will a precipitate form when 0.10 L of 8.0 x 10-3 M Pb(NO3)2 is added to 0.40 L of 5.0 x 10-3 M Na2SO4? Yankeeexposure. blogspot.com HW: 17.50

  38. CuS (Ksp = 6 x 10-37) is less soluble than ZnS (Ksp = 2 x 10-25) • If H2S is added to the green solution, black CuS precipitates first • If this precipitate is removed and more H2S is added, white ZnS forms • This is called selective precipitation Horrornews.net

  39. VII) Qualitative Analysis Media.weirdworm.com Media.weirdworm.com HW: 17.56, 17.58

  40. Nataliedee.com

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