CHEM 1062 Lecture Notes - Lecture 21: Chief Operating Officer, Sodium Hydroxide, Buffer Solution
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This equation works for the general reaction: 0. 25 m naf ph = 3. 14 + log (0. 25/1. 0) = 2. 54. Ka = 7. 72*10-4 pka = -log(ka) = -3. 14. Pick a weak acid with a pka close to desired ph. Pick a base acid concentration ratio to fine tune the ph. Design a buffer using c6h5cooh (pka = 4. 19) with ph = 4. 30 ph = pka + log([c6h5coo-]/[c6h5cooh]) Note: as the solution becomes more dilute (smaller concentration) causes buffer capacity to decrease. Start with 1. 0 l of 1. 0 m ch3cooh (pka = 4. 74) Way 1: add 0. 25 l of 1. 0 m ch3coona. Way 2: add 0. 25 l of 1. 0 m naoh. Number of moles ch3cooh = 1. 0 moles. Number of moles ch3coo- = 0. 25 moles. New [ch3cooh] = 1. 0 mole/1. 25 l = 0. 80 m. New [ch3coo-] = 0. 25 mole/ 1. 25 l = 0. 20 m. Ch3cooh + oh- ch3coo- + h2o. Number of moles of ch3cooh remaining: 0. 75 mole.
