Cabbage pH Lab                                                                                                                                              

pH is the -log[H+]. Acids increase the concentration of hydrogen ions ([H+]) in a solution and therefore have a low pH. A base will increase the concentration of hydroxide ions ([ OH-]) (decreasing the [H+]) in a solution and will have a high pH.

Background:

Several different plants, (hydrangeas, for example) produce blooms with different colors, depending on the pH of the soil. The color of many vegetables is also influenced by the pH of the soil in which they grew. Red cabbage, for example, contains a pigments called phycocyanin and phycoxanthin that will also respond to different pH by changing color. Such pigments are also found in red poppies, blue cornflowers, grapes, and apple skin.

The Challenge:

There are a series of solutions of unknown pH on the back table. Your task is to identify the pH of each solution. You will have access to a set of solutions, buffered to specific pH. They are labeled and on the common lab table in the back of the room. You may not use a pH meter.