patino_chm2046_chapter16

020 0020 x x 0020 x 0020 x 0 0 x x x x kb 16

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Unformatted text preview: H at equivalence point? equivalence Eq uiva le nc ee P o int Eq uiva le nc P o int Most important species in solution is benzoate ion, Bz --,, tthe Most important species in solution is benzoate ion, Bz the he the conjugate base of benzoic acid, HBz. conjugate base of benzoic acid, HBz. Bz-- + H2O ⇄ HBz + OH-Bz + H2O ⇄ HBz + OH Bz Bz [Bz--]] [[Bz [Bz Bz initial initial change change Equilib Equilib Equilib Equilib [HBz] [[HBz] [HBz] HBz] 0.020 0.020 -x -x 0.020 - x 0.020 - x 0 0 +x +x x x Kb = 1.6 x 10−10 Kb = 1.6 x 10−10 [[OH--]] OH 0 0 +x +x x x Ac id ­Ba s e R e a c tio ns Ac Q: Titrate 100. mL of a 0.025 M solution of benzoic acid with 0.100 M NaOH to the equivalence point. What is the pH at equivalence point? equivalence Eq uiva le nc e P o int Most important species in solution is benzoate ion, Bz -, the conjugate base of benzoic acid, HBz. Bz- + H2O ⇄ HBz + OHBz HBz 2 x Kb = 1.6 x 10-10 Kb = 1.6 x 10 ­10 = 0.020 ­ x x = [OH-] ≈ SQRT(0.020 × 1.6× 10−10)= 1.8 x 106 Q::Titrate 100. mL of a 0.025 M solution of benzoic acid with Q: Titrate 100. mL of a 0.025 M solution of benzoic acid with Q 0.100 M NaOH to the equivalence point. What is the pH at 0.100 M NaOH to the equivalence point. What is the pH at half-way point? (i.e.,12.5 mL added of the 25 mL needed for half-way point? (i.e.,12.5 mL added of the 25 mL needed for the equivalence point) tthe equivalence point) he the pH at half-way point? pH at half-way point? 1. <7 1. <7 2. =7 2. =7 3. >7 3. >7 @ equivalence @ equivalence equivalence equivalence point, pH = 8.25 point, pH = 8.25 point, point, pH at half-way pH at half-way pH pH mL) mL) mL) mL) point (12.5 point (12.5 Ac id ­Ba s e R e a c tio ns Ac Titrate 100. mL of a 0.025 M solution of benzoic acid Titrate with 0.100 M NaOH. with What is the pH at the half-way point? What HBz + H2O ⇄ H3O+ + Bz- Both HBz and Bz-- are Both HBz and Bz are present at same [[ ]= M present at same ]= M This is a BUFFER! This is a BUFFER! Ka = 6.3 x 10-5 + [HBz] [H 3 O ] = - • Ka [Bz ] At the half-way point, [HBz] =...
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