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Dr. T Presents:

Dr. T Presents:. The Henderson-Hasselbalch Equation. For more, please visit: http://www.ChemistryWithDrT.com/. The Henderson-Hasselbalch Equation. What is it? Used to quickly calculate the pH of a buffer solution.

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Dr. T Presents:

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  1. Dr. T Presents: The Henderson-Hasselbalch Equation For more, please visit: http://www.ChemistryWithDrT.com/

  2. The Henderson-Hasselbalch Equation • What is it? • Used to quickly calculate the pH of a buffer solution. • Buffer: A solution containing a weak conjugate acid-base pair that is able to accommodate the addition of strong acids and bases without the pH of the solution changing much. • It is based on some underlying assumptions (later in video). • Advantage: The concentrations of the buffer components can be used directly rather than using an ICE chart (always write the chemical equation). • Derivation: Can be found in your textbook or class lectures.

  3. The Henderson-Hasselbalch Equation • What is it used for? • Used to quickly calculate the pH of a buffer solution. • Biologists – Buffers for cell growth media • Biochemists – Buffers for enzyme kinetics assays • Chemists – Buffers for pH sensitive chemical reactions • Students – Buffers for laboratory experiments

  4. The Henderson-Hasselbalch Equation • How is it used? • Problem: • 0.20 mol of benzoic acid and 0.10 mol of sodium benzoate are dissolved in 1 L pure water. What is the pH of this solution? • Given: Ka of benzoic acid = 6.3 x 10-5

  5. The Henderson-Hasselbalch Equation 0.20 mol of benzoic acid and 0.10 mol of sodium benzoate are dissolved in 1 L pure water. What is the pH of this solution? Given: Given: Ka of benzoic acid = 6.3 x 10-5

  6. Tips & Tricks • Assumption made by the Henderson-Hasselbalch Equation: • The amount of acid that ionizes in solution is negligible compared to the amount of acid and conjugate base that are used to form the buffer. • What it means for you: • The Henderson-Hasselbalch equation is inappropriate to calculate the pH of a solution containing only a strong acid or a strong base. • Be sure that the amount of acid and conjugate base added are at least 102 larger than the Ka.

  7. Tips & Tricks • pH and Buffer Capacity • The pH of the buffer solution is determined by the Ka of the conjugate acid. • The amount of acid or base that can be added to the system and neutralized by the buffer before the pH changes by a significant amount depends on the amount of conjugate acid and conjugate base used to make the buffer. (Buffer capacity) • For example: • A solution of 1 M benzoic acid and 1 M sodium benzoate has the same pH of a solution containing 0.1 M benzoic acid and 0.1 M sodium benzoate. The 1 M solution has a larger buffer capacity, and can therefore neutralize a greater amount of added acid or base.

  8. THANK YOU!!! For more resources, please visit: http://www.ChemistryWithDrT.com/

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