Red Cabbage Lab

Introduction:

Liquids and solids all around us have either acidic or basic (alkaline) properties. For example,acids taste sour; while, bases taste bitter and feel slippery. However, both strongacids and strong bases can be very dangerous and burn your skin, so it is important tobe very careful when using such chemicals. In order to measure how acidic or basic aliquid is, one must use the pH scale as illustrated below:

The strength of the pH scale is determined by the concentration of hydrogen ions(H+) where a high concentration of H+ ions indicate a low pH and a lowcon cent ration of H+ ions indicate a high pH. The pH scale ranges from 1 to 14where 1 to 6 is classified as acidic, 7 neutral (neither a base or an acid) and 8 to 14 isclassified as basic.

In this lab, you will use the juice from red cabbage as a pH indicator to test commonhousehold liquids and determine their pH levels. You will mix cabbage juice withdifferent household liquids and see a color change produced by a pigment called flavin(an anthocyanin) in red cabbage. Through this color change, you will be able tosuccessfully identify the approximate pH of common household liquids using the tablebelow:

Purpose: To test some common substances with an indicator prepared from red cabbage.

1-6.9Acidic7=Neutral7.1-14 Basic

pH / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14
Red- / Light / Blue / Yellow-green
Color / Red / Brown / Blue / Blue-Green / Green / Yellow
Purple / Purple
Purple
Table 1: pH and the color of Red Cabbage Indicator
Materials :
Red (purple) cabbage / Test substances:
250 ml beaker / -Borax
100 ml beaker / -Baking Soda
Water / -Detergent
Hot plate / -Glass Cleaner
Gauze heating pad / -Hand Sanitizer
-Soda Pop
6 test tubes
Test tube rack
Pipette

Pre Lab Predictions:

Predict whether the items to be tested will be Neutral, Acidic, or Basic. (Circle your choice)

BoraxBasicNeutralAcidic

Baking SodaBasicNeutralAcidic

DetergentBasicNeutralAcidic

Glass CleanerBasicNeutralAcidic

Hand SanitizerBasicNeutralAcidic

Soda PopBasicNeutralAcidic

Method:

  1. Tear a leaf from the red cabbage into small pieces and place them in a 250 ml beaker.
  1. Cover the cabbage with water. Place the beaker on the gauze pad on the hot plate.
  1. Boil the cabbage for about 5 minutes or until the water is a deep purple colour.
  1. Cool the contents of the beaker and pour off the liquid into the 100 ml beaker.
  1. While you are waiting for the indicator to be ready, prepare your test tubes. Add 1cm of each substance to the test tubes according the observation chart below. Label test tubes if needed.
  1. When the indicator is ready, place a little bit into each test tube. Record your observations.

Red Cabbage Lab

Purpose: To test some common substances with an indicator prepared from red cabbage.

pH / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14
Red- / Light / Blue / Yellow-green
Color / Red / Brown / Blue / Blue-Green / Green / Yellow
Purple / Purple
Purple
Table 2: Red Cabbage Indicator and Various Household Substances
Test Tube / Borax / Baking Soda / Detergent / Glass Cleaner / Hand Sanitizer / Soda
Pop
Color of Indicator
Approximate pH
Acid or Base?

Analysis:

  1. Why is it difficult to determine the pH accurately using red cabbage?
  1. You walk into your kitchen and saw an unknown substance on the floor. Describe what would do, using a cabbage head, to test the substance to find the pH. Explain what you may see.

3. Why and when does red cabbage juice changes from purple to other colors?

  1. List the substances you tested from most acidic to most basic.