Acids and Bases: Experiment on Red Cabbage

Please see document attached

BIOL 1014 Lab 6 Acids and Bases                         

Skill: Acids, Bases and pH

Purpose:

Using red cabbage as a pH indicator, several household items will be tested to determine their degree of acidity or alkalinity.  On the pH scale, “7” is considered neutral.  Below 7 on the scale is the acidic range (0 to 6.9); above 7 on the scale is the basic range (8 to 14).  Strong acids are found near the far left of the scale (near zero), while strong bases are found near the far right of the scale (near 14). Flavin is a pigment molecule found in red cabbage.  Acidic solutions cause the pigment to turn reddish.  Basic solutions will cause the pigment to turn greenish-yellow.  Knowing this (and using the chart below) you can determine the approximate pH of your unknowns.

Remember, only a pH of EXACTLY 7.0 is considered neutral.

MATERIALS NEEDED:

Red cabbage

Boiling water

Large drinking glass or other glass container

6 small drinking glasses or glass jars

Household ammonia (such as Windex or 409)

Vinegar

Baking soda

Soda pop (Coke, Dr. Pepper, etc)

And 2 items of your choice (liquids work best or powders you can mix with the cabbage juice)

PROCEDURE:

1.  Chop the red cabbage into small pieces until you have about 2 cups of chopped cabbage. 

2.  Place the cabbage into the large drinking glass and add boiling water to cover the cabbage.  Allow at least 10 minutes for the color to leach out of the cabbage. 

3.  Filter out the plant material with a fork so that just the liquid is left in the container.  The liquid should be purple-bluish in color (pH of approximately 7).  

(Alternatively, you can add the cabbage to water in a pan on the stove and just bring the water to a boil and then turn it off.  Let it stand until it is cool enough to work with and strain out the cabbage.  (By the way, cabbage is tasty, put on some salt and pepper and eat it after!))

4.  Pour the red cabbage indicator solution evenly into your 6 small glass containers (approximately ¼ to ½ full).  Reserve a small amount for the final question

5.  When you start adding your unknowns, you will want to gradually add until you notice a color change.  Add ammonia to the 1^st glass, vinegar to the 2^nd glass, baking soda to the 3^rd glass, and soda pop to the 4^th glass.  For your last two glasses, you can add 2 items of your choice.