A buffer solution is a solution that changes pH only slightly when small amounts of a strong acid or a strong base are added.

A buffer contains significant concentrations of both a weak acid and its conjugate base, or

a weak base and its conjugate acid.

This buffer relies on the dissociation reaction of acetic acid.

CH3COOH CH3COO- + H+

Buffer animation

Our blood is buffered to a pH of 7.4 Buffers are used when pH must be

controlled in experiments.Proteins Enzymes

Pure water increases in pH by about 5 pH units when the OH– is added, and decreases by about 5

pH units when the H3O+ is added.

In contrast, the same amounts of OH– and H3O+ added to a buffer solution barely change the pH.

There is a limit to the ability of a buffer solution to neutralize added acid or base.

This buffer capacity is reached before either buffer component has been consumed.

As a rule, a buffer is most effective if the concentrations of the buffer acid and its conjugate base are equal or nearly so.

Determine the buffer capacity of 3 different concentrations of sodium acetate buffer using an acid and a base.

We will be using HCl and NaOH so you must wear lab coat, goggles, and gloves at all times!

1. Label one 250 mL beaker acid and the other one base.

2. Pour 50 mL of 1.0 M acetic acid buffer into each of the beakers.

3. In the beaker labeled base, add 1 mL of Universal Indicator. In the beaker labeled acid, add 1 mL methyl orange.

4. Measure and record the pH of each solution.

5. Using a disposable pipet, add 1 mL of 1.0 M HCl to the beaker labeled acid. Mix well. Measure and record the pH.

6. Continue adding HCl 1 mL at a time until the pH and the color of solution changes.

7. Repeat steps 5-6 using the NaOH and the base beaker.

8. Rinse both beakers out and repeat steps 3-7 using the 0.1 M buffer and then the 0.01 buffer.

Make a Data Table to record your pH values.

Buffer Concentration

mL of HCl pH mL of NaOH pH

1.0 M

0.1 M

0.01

Graph your data with pH on the y-axis and volume of acid/base on the x-axis.

Don’t forget to include the units and titles for each axis. Your graph should also have a main title and a legend.

1. How does the concentration of the buffer affect the buffer capacity?

2. How is the HCl graph different from the NaOH graph?

3. Write reaction equations to explain how your acetic acid-acetate buffer reacts with an acid and reacts with a base.

4. What is the buffer capacity of each buffer used (for both HCl and NaOH)?