Red Cabbage Juice pH Indicator
Sources: Prof. George Ewing's C100 Demonstration Notes; Prof. Carolyn Huffman's Fall '93 C100 lecture; B. Z. Shakhashiri, 1989, Chemical Demonstrations: A Handbook for Teachers of Chemistry, vol. 3, pp 162-166.
Description and Concept: Red cabbage juice will change to a variety of colors when added to solutions of various pH. Red cabbage juice is a pH indicator.
hot or boiling water
filter paper (coffee filters work well)
1 liter beaker
Six 250 mL beakers
Professors/Instructors please specify which chemicals you wish to use. Some that we may have on hand are: household ammonia (NH3)
baking soda (sodium bicarbonate, NaHCO3)
washing soda (sodium carbonate, Na2CO3)
lemon juice (citric acid, C6H8O7)
vinegar (acetic acid, CH3COOH)
cream of tartar (Potassium bitartrate, KHC4H4O6)
Other household items that may be used include:
antacids (calcium carbonate, calcium hydroxide, magnesium hydroxide...), seltzer water (carbonic acid, H2CO3),
muriatic acid or masonry's cleaner (hydrochloric acid, HCl), or lye (potassium hydroxide, KOH or sodium hydroxide, NaOH).
Hydrochloric acid and Sodium Hydroxide are strong irritants.
You should wear safety goggles and disposable gloves for this demo, especially if you choose to use HCl and NaOH.
Chop cabbage into small pieces.
Put cabbage in 5 liter beaker and then cover with boiling water, let stand for 10 minutes or more (the more you wait the more potent your indicator). OR
Put about 2 cups of cabbage in a blender, cover with boiling water, and blend. Filter out the plant material to get the red-purple-bluish colored liquid. This liquid is at about pH 7.
Pour about 50 - 100 mLs of your red cabbage indicator into each 250 mL beaker. Add your indicator to various household solutions until you see a color change. For example: Ammonia will turn...
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