Acids and Bases

Introduction

Organisms are often very sensitive to the effect of acids and bases in their environment. They need to maintain a stable internal pH in order to survive – even in the event of environmental changes. Many naturally occurring biological, geological, and man-made chemicals are capable or stabilizing the environment’s pH. This may allow organisms to better survive in diverse environments found throughout the earth.

In this investigation, you will test a number of substances using pH paper and a pH electrode to determine pH values of household substances. You will also examine the difference between qualitative and quantitative data.

Objectives

In this experiment you will: • Add an acid to a material and note the changes in pH • Add a base to a material and note the changes in pH • Work with classmates to compare the ability of different materials to test pH

[pic]
Figure 1

Materials

Computer Vernier computer interface LoggerPro Vernier pH sensor Paper towel
Wash bottle with distilled water
Goggles
Beaker
24-well plate pH paper

Procedure

Part 1: pH tests using pH paper

1. Obtain and wear goggles.

2. Notice the 24-well plate is labeled with A-D for the rows and 1-6 for the columns.

3. Have ONE group member go to the back lab bench and fill the wells halfway with the various household substances.

4. Take a piece of the pH paper and touch it to the substance in well A1.

5. Observe the reaction and record the results in the data table provided.

6. Compare the color of the pH strip to the key on the side of the pH container. Write the correct pH value in the data table.

7. Repeat steps 4-6 for the remaining substances.

Part 2: pH tests using Vernier pH sensor

1. Before each use of the pH probe, you need to rinse the tip of the