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Indicators

Acid color. InH ( aq .) ⇌ H + ( aq .) + In – ( aq .). Base color. Indicators. CHEM 114 Lecture 6 1/26/2011. Thymol blue. Acid color. Neutral color. Base color. CHEM 114 Lecture 6 1/26/2011. Strong acid strong base titration. CHEM 114 Lecture 7 1/28/2011.

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Indicators

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  1. Acid color InH (aq.) ⇌ H+ (aq.) + In– (aq.) Base color Indicators CHEM 114 Lecture 6 1/26/2011

  2. Thymol blue Acid color Neutral color Base color CHEM 114 Lecture 6 1/26/2011

  3. Strong acid strong base titration CHEM 114 Lecture 7 1/28/2011

  4. Strong base strong acid titration CHEM 114 Lecture 7 1/28/2011

  5. Weak acid strong base titration CHEM 114 Lecture 7 1/28/2011

  6. Weak acid strong base titration CHEM 114 Lecture 7 1/28/2011

  7. We add 50 mL a 0.1 M solution of AgNO3 to 50 mL of a 0.1 M solution of KI AgNO3 (s) → Ag+ (aq) + NO3– (aq) NaI (s) → Na+ (aq) + I– (aq) Solubility When the solutions are mixed, four kinds of ions are present (neglecting H+ and OH–) However, two of the ions precipitate to give a solid. It’s easy to prove the solid is AgI Ag+ (aq) + I– (aq) → AgI (s) This is written as a unidirectional reaction, but it’s actually an equilibrium Ag+ (aq) + I– (aq) ⇌ AgI (s) The activity of a pure solid is 1, so solubility equilibria usually have no denominator. The special name we give to a solubility equilibrium constant is the solubility product CHEM 114 Fundamental Chemistry Ksp = aAg+aI– = 8.5 × 10–17 @ 25°C

  8. Solubility products CHEM 114 Fundamental Chemistry

  9. If we could assume that activities were concentrations, we could use the solubility product to calculate the molar solubility of AgI Ag+ (aq) + I– (aq) ⇌ AgI (s) aAg+aI– = 8.5 × 10–17 ~ [Ag+][I–]/M2 Solubility products and activities If x moles of AgI (s) dissolves, then [Ag+][I–] = x2; x = 9.2 ×10–9 M. So the solubility of AgI in water at 25° C is 9.2 ×10–9 M This is a good approximation in very dilute solution (< 10–6 M) and a fair approximation in semi-dilute solution (< 10–4 M). To be accurate it needs adjustment for the activity coefficient : aAg+ = γAg+ [Ag+] For water at 298 K Aγ = 1.17 mol–1/2 kg1/2 uncharged solute I = ½ ΣZi2mi As I increases, ln γ becomes more negative, and γ decreases CHEM 114 Fundamental Chemistry ionic solute

  10. 2Ag+ (aq) + CrO42– (aq) ⇌ Ag2CrO4 (s) Ksp = aAg+2aCrO42– = 1.1 × 10–12 @ 25°C 4x3 = 1.1 × 10–12 so x = 6.5 × 10–5 Common ion effect CHEM 114 Fundamental Chemistry

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