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BUFFER SOLUTIONS LAB 9. INTRODUCTION Adding trace amount of acid to water will result in increase in H + concentration. In the same manner, adding trace.

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Presentation on theme: "BUFFER SOLUTIONS LAB 9. INTRODUCTION Adding trace amount of acid to water will result in increase in H + concentration. In the same manner, adding trace."— Presentation transcript:

1 BUFFER SOLUTIONS LAB 9

2 INTRODUCTION Adding trace amount of acid to water will result in increase in H + concentration. In the same manner, adding trace amount of alkali eg. NaOH to pure water will result in increase of OH − So we can say that water has no ability to resist change in H + concentration or pH. (pH = − log [H + ])

3 WHAT IS A BUFFER SOLUTION? Buffer solution: Is a system that possesses the property of resisting change in the pH with the addition of small amount of strong acid or base. The efficiency of the system called buffer capacity.

4 COMPOSITION Buffer solution is usually composed of a weak acid and a salt of the acid eg. Acetic acid and sodium acetate, or weak base and a salt of the base eg. Ammonium hydroxide and ammonium chloride.

5 WEAK ACID BUFFER

6 Dissociation constants of some weak acids at 25 °C ACID Acetic acid1.75 x Benzoic acid6.4 x Formic acid1.76 x Lactic acid1.38 x Salicylic1.06 x 10 -3

7 WEAK ACID BUFFER

8 WEAK BASE BUFFER

9 PRACTICE PROBLEMS 1.the dissociation constant K a of acetic acid is 1.75 x at 25 °C. Calculate its pK a value. 2.What is the pH of a buffer solution prepared with 0.05 M sodium borate and M boric acid? The pK a of boric acid is 9.24 at 25 °C. 3.What is the pH of a buffer solution prepared with 0.05 M ammonia and 0.05 M ammonium chloride? The K b of ammonia is 1.8 x at 25 °C. 4.What molar ratio of salt/acid is required to prepare a sodium acetate-acetic acid buffer solution with a pH of 5.76? pK a of acetic acid is 4.76 at 25 °C.

10 PRACTICE PROBLEMS 5.The molar ratio of sodium acetate to acetic acid in a buffer solution with a pH of 5.76 is 10:1. Assuming the total buffer concentration is 2.2 x mol/L, how many grams of sodium acetate (m.w. 82) and how many grams of acetic acid (m.w. 60) should be used in preparing a liter of the solution? 6.Calculate the change in pH after adding 0.04 mol of sodium hydroxide to a liter of buffer solution containing 0.2 M concentration of sodium acetate and acetic acid. The pK a of acetic acid is 4.76 at 25 °C. 7.What is the pH of buffer solution prepared with M sodium acetate and 0.01 M acetic acid? The pK a of acetic acid is 4.76 at 25 °C.

11 HOME WORK 1.What is the change in pH with addition of 0.01 hydrochloric acid to a liter of buffer solution containing 0.05 M of ammonia and 0.05 M ammonium chloride? K b of ammonia is 1.8 x at 25 °C. 2.The dissociation constant of ethanolamine is 2.77 x at 25 °C. Calculate pK b


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