Name:
Date:
Period:
Acids, Bases, and pH
What is pH, and what does pH tell you?
Standard 5e:
Students know how to determine whether a solution is acidic, basic, or neutral.
Introduction:
pH is a number that shows whether a solution is an acid, a base, or neutral. Acids are
solutions that have a pH less than 7. Bases (or alkalis) are solutions that have a pH
greater than 7. A pH of 7 is called a neutral solution. pH is important because most
living things can only survive in a narrow range of pH. For example, if the pH of the
water in an aquarium becomes too low (acidic) or too high (alkali), the fish in the
aquarium cannot survive. As you work, you will find the pH of several common solutions
you probably encounter all the time. You will also learn some of the properties of acids
and bases.
Materials: Each Lab Group will have the following

2 ceramic spot plates (these are fragile, please be careful with them)

9 Pipettes

Red cabbage juice

Red and blue litmus paper

10 solutions

White paper

Paper towels

Goggles for each student
Procedures:
**Put on Safety Goggles
Part 1: Make a pH scale using indicators
Step 1:

Place a spot plate on top of a piece of white paper.

Label on the white paper next to one well of the spot plate each: #1, #2, #3, #4,
and #6. (1 number by each well)

Use 1 pipette to put 3 drops of cabbage juice into each of the 5 wells of the spot
plate that’s on the paper.

Save this pipette for a later step- don’t get it mixed up along the way with other
pipettes.
Step 2:

Pick out 5 pipettes, you will use a different one for each solution.

Add 2 drops of solutions #1, #2, #3, #4, and #6 to each of the corresponding
wells on the spot plate. (make sure this corresponds to your numbers on your
paper)

Write down the color changes that you see when you add the two drops of each
solution. The series of color that you see on the spot plate represents a pH scale.
Step 3:

Dip red and blue litmus paper into each well of the spot plate.

Observe any color changes in the litmus paper.

Use the data table to record what you see.
Data Table:
Evaluating the role of the pH Test plate
1. What is the role of a pH indicator? You used three different indicators, red
cabbage juice, red litmus paper and blue litmus paper. What is the range of pH
measured by each of them?
2. What general color do basic solutions turn when added to red cabbage juice?
3. What general color do acidic solutions turn when added to red cabbage juice?
* Keep your original spot plate with the solutions in them to compare for the next 2 parts
of this lab.
Part 2: Using pH indicators to measure unknown pH
Step 1:
 Get a clean spot plate and place it on the white paper.

Label on the white paper next to one well of the spot plate each: #7, #8, #9.

Use the pipette that you used for cabbage juice and place 3 drops of cabbage
into each of the 3 wells of the spot plate.
Step 2:

Select 3 clean pipettes. Use one pipette per solution.

Add 2 drops of solutions #7, #8, #9 to the corresponding well of your spot plate.

Write down the color changes that you see when you add the two drops of each
solution.
Step 3:

Dip red and blue litmus paper into each well of the spot plate.

Observe any color changes in the litmus paper.

Use the data table to record what you see.

Find the approximate pH of your three new solutions by looking at the color
changes that happened when you added two drops of each to the red cabbage
juice. Compare these color changes with your previous test plate (known pH).
Part 3: Identifying Mystery Solutions
Step 1:

Add 3 drops of cabbage juice to 2 empty wells of your spot plate. (use the
pipette you’ve been using for cabbage juice.

Label one well Mystery A and the other Mystery B.
Step 2:

Select 2 clean pipettes. Use one for each mystery solution.

Add 2 drops of each mystery solution to the 2 wells of cabbage juice you created.

Step 3:

Dip red and blue litmus paper into each well of the spot plate.

Observe any color changes in the litmus paper.

Use the data table to record what you see.
Mystery solutions A and B are the same as two other solutions that you used in this
investigation. Use your original spot plate with your pH indicators to determine what the
mystery solutions are.
1. What is the name of mystery solution A?
2. What is the name of mystery solution B? Give evidence to support your answers.
Clean Up Instructions:

Return solutions to teacher. (Do NOT pour liquids out)

Put pipettes and spot plates in water container.

Return safety goggles to teacher.

Clean any spills and return towel to teacher.

Throw away white paper and paper towels.

Turn in lab sheet.