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Experiment Testing the Effectiveness of a Buffer Experiments​

Testing the effectiveness of a buffer.

Experiment #16 from Vernier Chemistry Investigations for Use with AP* Chemistry

Introduction

A buffer is an aqueous mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid. A buffer has a very stable pH. When small amounts of an acid or a base are added to a buffer solution, the pH of the solution changes very little. In many chemical and biochemical systems, buffers are critical. Blood plasma, a natural example in humans, is a bicarbonate buffer that keeps the pH of blood between 7.2 and 7.6.

By design, a buffer is an equilibrium system. An example is a buffer prepared with nitrous acid, HNO 2 . The weak acid establishes an aqueous equilibrium as shown below:

{\text{HNO}}{_{\text{2}}}{\text{ (aq)}} \to {\text{H}}{^{+}}{\text{ (aq) + NO}}{_{\text{2}}}{^{\text{-}}}{\text{ (aq)}}

The equilibrium constant expression is

K{_{a}} = \frac{[{\text{H}}{^{+}}][{\text{NO}}{_{2}}{^{-}}]}{[{\text{HNO}}{_{2}}]}

To prepare a buffer system with nitrous acid, a conjugate base, such as sodium nitrite (NaNO 2 ), is added. The resulting system is a mixture of HNO 2 and NO 2 – ions. The nitrous acid molecule will buffer the addition of an acid and the nitrite ion from the conjugate will buffer the addition of a base.

A variation of the equilibrium expression above, called the Henderson-Hasselbalch equation, is a very good reference in preparing a buffer solution. For a nitrous acid/sodium nitrate buffer, the Henderson-Hasselbalch equation is shown below:

pH = pK{_{a}} + log \frac{[{\text{NO}}{_{2}}{^{-}}]}{[{\text{HNO}}{_{2}}]}

The pH range in which a buffer solution is effective is generally considered to be ±1 of the pK a .

In the Initial Investigation, you will prepare two acetic acid/sodium acetate buffer systems. After examining the factors involved in preparing these buffers and testing their effectiveness, you will design a buffer for a specified pH range as well as test its effectiveness; effectiveness will be assessed based on the amount of acid or base a buffer can absorb before the pH of the buffer solution falls outside a specified pH range.

Sensors and Equipment

This experiment features the following sensors and equipment. Additional equipment may be required.

buffer experiment chemistry

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This experiment is #16 of Vernier Chemistry Investigations for Use with AP* Chemistry . The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.

buffer experiment chemistry

IMAGES

  1. Buffer Solutions (A-Level)

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  2. Experiment for the Preparation of Basic buffer solution

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  3. TRU Chemistry Labs: Experiment Titration Curves Part B

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  4. Buffers, Buffer Components and Buffer Action

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  5. O Sistema Detectou A Saturação De Um Buffer

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  6. Buffer Definition and Examples in Chemistry

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VIDEO

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