Cabbage Juice Lab

Purpose:To test the pH of different solutions

using cabbage juice.

Why use cabbage juice?

• By boiling the red cabbage leaves, we extracted a class of pigment molecules called anthocyanins into solution. Anthocyanin molecules will change their color depending upon the pH of their environment and can indicate the pH of a solution.

What is pH?

• The pH scale measures how acidic or basic a substance is.

• It ranges from 0 to 14. • A pH of 7 is neutral. • A pH less than 7 is

acidic, and a pH greater than 7 is basic.

• pH stands for (power of Hydrogen)

What should SOIL pH be to help plant growth?

Most soils for plant growth should be around 6 to 7 (slightly acidic to neutral) for optimal growth. If it is too acidic, lime can be added to raise the pH level.

If the pH of the soil is too acidic, this may slow down the decomposition process of bacteria.

Swimming Pool water pH

The pH is one of the most important factors in pool water balance and it should be tested and corrected at least every week. A pH of 7.0 is neutral - below 7.0 is acidic, above 7.0 is alkaline. The pH of our eyes is 7.2 . No wonder that the ideal pH for your pool is just that - 7.2 , and should be kept within the range of 7.0-7.6 . The wrong pH can hurt the pool filter, liner, and other parts that make up the pool.

Investigation

• Identify each solution as either an acid, base, or neutral.

Safety

• Wear goggles• No horseplay/running – avoid spills!• Do not eat or drink in the lab.• Clean up when finished • Dispose of chemicals according to teacher’s

directions.• Keep pipettes separated (they are labeled for

each solution).

Investigation Jobs

• Materials Manager – picks up supplies and returns them when finished.

• Recorder – makes sure that the data is written down (all will fill out chart, but recorder will make sure the data is recorded)

• Safety Officer – picks up goggles for group and returns them when finished.

• Director – makes sure that all participate with investigation

Procedure:1. Place a small amount of cabbage juice into the 8 compartments labeled 1 – 8. Use the pipette and be careful not to spill.2. One bottle at a time put about 5 drops of the substance into the compartments. Use the stick to stir slightly.3. Record the color changes in the chart.

•If the color is pink to red, it is an acid.•If there is no change, it is neutral. •If the color is blue/green/yellow, it is a base.

Solution 1

Vinegar

ChartCompartmentNumber

Solution Color after stirring? Acid/BaseOr Neutral?

1

2

3

4

5

6

7

8

ChartCompartmentNumber

Solution Color after stirring? Acid/BaseOr Neutral?

1 Vinegar2

3

4

5

6

7

8

Test it!

• Send materials person to get pipette of vinegar.

•If the color is pink to red, it is an acid.•If there is no change, it is neutral. •If the color is blue/green/yellow, it is a base.

Solution 2

Soda

Solution 3

Tap Water

Solution 4

Baking Soda

Solution 5

Milk

Solution 6

Soapy Water

Solution 7

Lemon Juice

Solution 8

Hand Sanitizer

Results!

Solution 1

Vinegar

pH: 3-4 (acid)

Solution 2

Soda

pH: 3 (acid)

Solution 3

Tap Water

pH: 7 (neutral)

Solution 4

Baking Soda

pH: 8-9 (base)

Solution 5

Milk

pH: 6 (acid)

Solution 6

Soapy Water

pH: 12 (base)

Solution 7

Lemon Juice

pH: 2-3 (acid)

Solution 8

Hand Sanitizer

pH: 7 (neutral)