Melaku Michael (ethiomelaku2) Directions: Copy the data table at the end of this lab into a word document. Fill in the data table after doing the lab and submit into the pH Lab with Cabbage dropbox. Overview: Acids are materials that have certain properties in common. Bases (also called alkalis) are other substances with a different set of properties. In this lab, you will investigate some of the substances found in your home and tell whether they are acids or bases. An indicator is a substance that changes color depending on whether it is in contact with an acid or a base. Purpose: Make your own acid/base indicator by boiling red cabbage. Use the juice to test the pH of different fluids. Materials: 1. 1/2 head of *red* cabbage or so. 2. Metal grater. 3. Pot filled with enough water to cover the grated cabbage. 4. Strainer 5. Household substances to test: vinegar, lemon juice, milk, laundry detergent, shampoo, baking soda. It might also be interesting to collect some fresh rain water in a clean plastic cup and test it also. Safety: Be careful with the fingers when grating the cabbage. You should have an adult present to help you. How to do the experiment: 1. Grate the cabbage into small pieces and place them in the pot + water. 2. Boil the mixture for 20-30 minutes, until the liquid turns a dark purplish color. 3. Decant the fluid into a glass or jar, pouring through a strainer to remove the cabbage. 4. Pour a small amount of each of the household items into plastic cups. It's useful to have a control solution of (neutral) water - distilled water is best if you have access to it. 5. Add a few drops of the cabbage juice to your solutions, and note any color changes. The juice should turn pink in acidic solutions, and green in basic solutions. Test your control (water) to be sure the cabbage juice color remains constant.
Explanation: Red cabbage contains pigments call anthocyanins. The pigments give it the red/purplish color. Anthocyanins belong to group of chemical compounds called flavonoids. For most pH indicators, the compound acquires a proton at low pH (lots of H+) but loses it at higher pH. This seemingly minor alteration is sufficient to alter the wavelengths of
light reflected by the compound, thus creating the color change with respect to pH. Anthocyanins behave somewhat inversely in that the pigments "gain" an -OH at basic pH, but lose it at acidic pH.
Data: Fill in the table below to show your collected results. Household substance Vinegar Lemon Juice Milk Detergent Baking soda Tap Water Rain Water Color after adding cabbage juice Dark Pink Dark Pink Dark Green Light Green Light Green Very light Pink Light Pink Acid, Base or Neutral? Acid Acid Base Base Base Neutral Acidic