Chem. Concepts: BuffersA General Overview

Eric Liu

Mr. Michael Gangluff

Chemistry AP

What is a “Buffer”?

A buffer is a solution that resists changes in pHA buffer is a solution that resists changes in pH

when small amounts of acid or base are added to it.when small amounts of acid or base are added to it.

What is it made of?

Acidic buffers Consists of a weak acid and a salt of its

conjugate base e.g. CH3COOH and CH3COONa

pH less than 7

Basic buffers Consists of a weak base and a salt of its

conjugate acid e.g. NH3 and NH4Cl

pH greater than 7

Buffers can be placed into two categories: acidic buffers and basic buffersBuffers can be placed into two categories: acidic buffers and basic buffers

Our blood is a buffer, as cells can only survive within a narrow pH range

The pH of a buffer can be changed by altering the ratio of acid and its conjugate base or base and its conjugate acid. The amount of acid/conjugate base or

base/conjugate acid determine its buffer capacity, or amount of acid or base that can be added for it to still maintain constant pH

How does it work?

Buffers follow one of the following equilibriums:

There are both products and reactants present in both cases

Buffers use Le Chatelier’s Principle, which states that a system will relieve stress put on a system by “shifting” to the left or right side of the equation accordingly.

In other words, if you add reactant to the equilibrium, the system would respond by removing reactant (and thus creating product), and vise versa

OHAOHHA 32 OHHBOHB 2

How does it work?

The H3O+ from the acid will cause the system to shift left

Or react with OH- to form H2O

If acid is added to the system…

OHAOHHA 32+

++++

OHHBOHB 2

How does it work?

The OH- from the base will cause the system to shift to the left

Or react with H3O+ to form H2O

If base is added to the system…

OHAOHHA 32

OHHBOHB 2+

++++

Summary

Buffers are solutions that resist changes in pH with the addition of small amounts of acid or base

They consist of a weakweak base and its conjugate acid salt or a weak weak acid and its conjugate base salt

They work through Le Chatelier’s Principle, shifting to the left or right to counterbalance the addition of acid or base