Ionic Equilibria.docx - Ionic Equilibria Nandita G Das PhD RPh Learning Objectives Review pH pKa and the Henderson Hasselbalch equation Predict

Ionic Equilibria.docx - Ionic Equilibria Nandita G Das PhD...

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Ionic Equilibria Nandita G. Das, PhD, RPh Learning Objectives: Review pH, pKa and the Henderson Hasselbalch equation Predict resultant pH (acidic or basic) of solutions when pharmaceutical salts are added to water Define buffers and buffering action Understand buffer capacity and appropriate application of the same in pharmacy practice Understand the buffering action in our blood system Learn about some commonly used buffer systems in pharmacy practice Ionization refers to the complete separation of the ions of a crystal lattice when a salt is dissolved. The ions in solution may be associated by inter-ionic attraction and may not exist as individual ions; the separation of these ions in solution is known as dissociation . Sorensen's pH scale Sorensen established the term pH, which was originally written as pH + , to represent the hydrogen ion potential, and he defined it as the common logarithm of the reciprocal of the hydrogen ion concentration: 1 pH = log [H + ] and since the logarithm of 1 is zero, pH = - log [H + ] pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic (Neutral) Basic The “common ion effect” and the Henderson and Hasselbalch equation Henderson and Hasselbalch derived an equation by which the pH of a buffer solution consisting of a weak acid and its salt may be calculated. This is based on the consideration of the effect that the common ion of the salt has on the dissociation of the weak acid. [salt]
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pH = p K a + log [acid] A comparable relation may be derived for buffers composed of weak bases and the corresponding salt of a strong acid, [base] pH = p K w - p K a + log [salt] Determination of pKa pKa values are generally determined by titration. pH of an aqueous salt solution When a strong acid and a strong base react to form a salt, it is completely ionized. When the salt is dissolved it dissociates into anions and cations, and as no change occurs in hydrogen or hydroxyl ions, the solution is neutral.
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  • Fall '09
  • pH, buffer solution

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