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Red Cabbage Juice pH Indicator

Introduction: A liquid may be an acid, base, or neutral. The degree of acidity or basicity can be measured by using the pH scale. The scale is divided into three areas: Acid (readings below 7), neutral (reading of 7), and basic (readings above 7). Each division either increase or decreases the pH of a substance 10 times. The pH of 5 is ten times more acidic than a pH of 6. Water has a pH of 7 but when it mixes with air the suspended materials will either raise or lower its pH. Acid Rain is an example of this type of reaction. When an acid and a base are mixed together the pH moves toward neutral, this is called neutralization; because the pH is approaching neutral. Background: Red cabbage contains a pigment called flavin. This pigment is also found in red poppies, blue cornflowers, grapes, and apple skin. Depending on the pH of the fruit or plant the pigment will give a different color. This pigment can be used to indicate pH. pH Color 2 Red 4 Purple 6 Violet 8 Blue 10 Blue-green 12 green-yellow

Litmus turns red in an acid environment and blue in a basic one. Objective: The student will determine the pH of various substances and will also determine how some of these substances can affect the environment. 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. Materials: household ammonia (NH3) baking soda (sodium bicarbonate, NaHCO3) vinegar (acetic acid, CH3COOH) seltzer water (carbonic acid, H2CO3), muriatic acid or masonry's cleaner (hydrochloric acid, HCl), or lye (potassium hydroxide, KOH or sodium hydroxide, NaOH). Safety: Hydrochloric acid and any of these Hydroxides are strong irritants. You must wear safety goggles. If you get any on your hands you should immediately wash in the sink. Procedure: Pour about ½ inch of each of the 6 solutions into test tubes. Dip a piece of red and then blue litmus in each one and record your results. Pour about 30 mLs of your red cabbage indicator into a beaker. Pour about ½ inch into each of six test tubes. Record your results Try mixing some of the acid (low pH) test tubes with some of the basic (high pH) test tubes, and record what happens.

Clean-Up: All of the chemicals used in this demo can be washed down the drain with water. For your report you will recreate a data table. This one is here so that you can record experimental results. Do not hand this sheet in!!! TT # 1 2 3 4 5 6 Mix 1 mix 2 mix 3 Questions - answer on a separate lined sheet of paper. Be sure your answers are written in complete sentences that include enough of the question so that the reader can tell what the entire subject is about. 1. What is the pH of a neutral solution? 2. What is the pH range of an acidic solution? 3. What is the pH range of a basic solution? 4. Which solution(s) had a neutral or close to neutral pH? 5. Which solution had the highest pH? 6. Which solution had the lowest pH? 7. If a lake were turning acid because of acid rain, what might you add to bring the pH closer to neutral? Explain how what you did in the lab supports your answer. Solution(s) Red Litmus Blue Litmus Red Cabbage Juice Approx pH


Microsoft Word - pH Red cabbage.doc

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