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CHAPTER 15

CHAPTER 15. AP CHEMISTRY. COMMON ION EFFECT. If you have HC 2 H 3 O 2 (aq) <=> H + (aq) + C 2 H 3 O 2 - (aq) What would happen if you added the salt NaC 2 H 3 O 2 ? Addition of C 2 H 3 O 2 - would cause the system to shift to the left This is called the COMMON-ION EFFECT

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CHAPTER 15

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  1. CHAPTER 15 AP CHEMISTRY

  2. COMMON ION EFFECT • If you have HC2H3O2(aq) <=> H+ (aq) + C2H3O2-(aq) What would happen if you added the salt NaC2H3O2? • Addition of C2H3O2- would cause the system to shift to the left • This is called the COMMON-ION EFFECT • Page 682 example

  3. BUFFER • Prepared by adding both the weak acid HB and its conjugate base B- to water • [H+] = ka[HB] = ka nHB • [B-] nB- • Effect of adding strong acids or bases to a buffer • HB(aq) + OH-(aq) ---> H2O(l) + B-(aq) • B-(aq) + H+(aq) ---> HB(aq) • H+ and OH- ions are consumed so the pH is not affected • Buffered solutions are most effective when concentrations of H+ and base B- are about the same • Read chapters 19 and 20 notes are due the first day of fourth term

  4. CONTINUED • Henderson-Hasselbach equation is used in biology to calculate the pH of the buffer • pH = pka+ log [base] • [acid]

  5. ACID-BASE TITRATION • Read and study pages 699-711 • Titration curve • Graph of pH to concentration • strong acid - strong base page 697 • H+(aq) + OH-(aq) <=> H2O(l) k = 1/kw = 1/(1 X 10-14) • pH = 7, change rapidly as you near the end point

  6. CONTINUED • Weak acid-strong base • HA(aq) + OH-(aq) <=> A-(aq) + H2O(l) k =1/kb • pH > 7 at end point, change occurs slowly at end point • Strong acid-weak base • H+ (aq) + A-(aq) <=> HA(aq) k = 1/ka • pH < 7, at end point, change occurs slowly at end point • Titration of polyproptic acids • When neutralization steps are separated the substance will show a titration curve with multiple equivalence points

  7. INDICATORS • HIn(aq) <=> H+(aq) + In-(aq) In = indicator • HIn and In- have different colors, the wavelengths that bounce back are different when hydrogen is attached • Color of a solution depends on the concentration ratio • [HIn] = [H+] • [In- ] ka • Endpoint occurs when [H+] = ka • About pH 5 for methyl red, pH 7 for bromothymol blue, and pH 9 for phenolphthalein • Read pages 711-716

  8. SOLUBILITY EQUILIBRIA • If Q(ion product) is compared with the ksp, the following can be said • Q > ksp ppt occurs until Q = ksp • Q = ksp equilibrium (saturation has occured) • Q < ksp solid dissolves until Q = ksp • AgCl(s) <=> Ag+ (aq) + Cl- (aq) • Slightly soluble ksp found on page 718 • ksp = [Ag+][Cl-]

  9. CONTINUED • the solubility of slightly soluble salts containing basic anions will increase as the [H+] increases • Looking at the solubility of a salt • In pure water it is the same as the reaction

  10. CONTINUED • Complex ions • Metal ions with Lewis bases bonded to it page 958, 731-737 • Amphoterism • Behavior of water molecules around a metal ion • Read pages 724-730

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