Acids increase the proportion of hydrogen ions (H+) in solutions and bases increase the proportion of hydroxide ions
(OH-). The pH scale is used to determine the concentration of H+ and OH- ions in a given solution. Substances with a pH<7 are acids: the lower the number, the more H+ ions in the solution. Substances with pH>7 are alkaline (basic): the higher the number, the more OH- ions in the solution. An indicator is a substance that changes color at a particular pH (Acid-base, 2004). In this lab, a universal indicator was extracted from red cabbage and the pH color range calibrated compared to universal pH paper. The red cabbage indicator and calibrated color scale were then used to determine the pH of several household substances.
. Part 1: Investigation/Calibration of Red Cabbage Juice Indicator
10mL red cabbage juice was placed in a test tube and the pH determined. Ammonia as base was added dropwise, and after each drop was mixed in the solution, a drop was placed in a well of a well plate and the pH determined using universal pH paper. This was continued until the limit of the basic end of the spectrum was reached for red cabbage indicator (yellow color). The experiment was then repeated using vinegar as acid until the acid end of the red cabbage indicator was reached (red color).
Part 2: Determining the pH of Household Substances/Accuracy of the Red Cabbage Indicator
10 drops of each test substance were placed in a well of a well plate, along with 20 drops of red cabbage indicator. Solid substances were crushed and mixed with water for testing. The solutions were stirred, and the color of each solution recorded after at least 30 seconds. The pH of each test solution was determined using universal pH paper, the value recorded, and the chemical formulas of the test substances determined.
Acid-base indicators. (2004). Retrieved July 20, 2005 from: