(8.5) Buffers

What is a Buffer? Buffers are solutions that contain a weak acid/conjugate base mixture or a weak base/conjugate acid mixture

Purpose of a Buffer A buffer resists changes in pH when small amounts of acid or base are added. A buffer resists changes in pH when small amounts of acid or base are added. On a titration curve, the constant pH region is shown by a almost horizontal section (plateau) On a titration curve, the constant pH region is shown by a almost horizontal section (plateau)

Buffers and Basic Titrants Rapid increase in pH, but the rate of fall decreases Buffer resists changes in pH

Buffers and Acidic Titrants Buffer resists changes in pH

How to Make a Buffer Two ways: Two ways: 1.By using a weak acid and one of its salts Ex. Mix acetic acid and sodium acetate (CH 3 COOH & NaCH 3 COO) 2. By using a weak base and one of its salts Ex. Mix ammonia and ammonium chloride (NH 3 & NH 4 Cl)

Adding an Acid to a Buffer Adding an acid to a buffer (ex. CH 3 COOH/NaCH 3 COO), the acetate ions from the NaCH 3 COO react with the added H 3 O + Adding an acid to a buffer (ex. CH 3 COOH/NaCH 3 COO), the acetate ions from the NaCH 3 COO react with the added H 3 O + CH 3 COO - + H 3 O + CH 3 COOH + H 2 O Recall: LCP Added acid causes shift to the right to get rid of H 3 O + In this case the added H 3 O + are removed and pH is lowered slightly

Adding a Base to a Buffer Adding a base to a buffer (ex. CH 3 COOH/NaCH 3 COO), the acetic acid reacts with the added OH - Adding a base to a buffer (ex. CH 3 COOH/NaCH 3 COO), the acetic acid reacts with the added OH - CH 3 COOH + OH - CH 3 COO - + H 2 O Recall: LCP Added base causes shift to the right to get rid of OH - In this case the added OH - reduces amount of acetic acid present and pH is increased slightly

Buffer Capacity There is a limit to how much strong acid and strong base a buffer can neutralize before its pH changes drastically. There is a limit to how much strong acid and strong base a buffer can neutralize before its pH changes drastically. The buffer capacity depends on the concentration of buffer components. The buffer capacity depends on the concentration of buffer components. When their ratio of concentration components is close to 1, maximum capacity has been reached. When their ratio of concentration components is close to 1, maximum capacity has been reached.

Buffer Capacity Buffer Capacity :The amount of acid or base that can be added before a significant change occurs in pH. Buffer Capacity :The amount of acid or base that can be added before a significant change occurs in pH. Buffer capacity exceeded

Importance of Buffers Anywhere there is a narrow tolerance for pH changes Anywhere there is a narrow tolerance for pH changes Cell function & metabolism Cell function & metabolism Blood Blood Manufacturing of antibiotics Manufacturing of antibiotics Production of some dairy products Production of some dairy products