Lynne Andrew
NB 1110 / M 5 – 7:50
Lab 1
February 2, 2015

pH and Buffer – Using Red Cabbage Indicator to Measure pH

Introduction This experiment was performed to evaluate the following hypothesis: Red cabbage indicator can be used as a measure of pH. According to Campbell, et al, in Biology: Concepts and Connections, red cabbage contains a water-soluble pigment called anthocyanin that changes color when it is mixed with an acid or a base. The pigment turns red in acidic environments with a pH less than 7 and the pigment turns bluish-green in alkaline (basic) environments with a pH greater than 7 (2012). The pH indicating property of red cabbage indicator is well accepted in the scientific community and is a useful standard for us to become familiar with. As stated in the lab text, having a known set of standards is important to gaining information about unknowns (2011). Red cabbage contains high levels of anthocyanins, which give the cabbage its deep purple hue. The pigments also change in relation to changes in pH, according to the lab text (2011). According to a University College London lab experiment titled Red Cabbage pH Indicator, with most pH indicators, the compound gains a proton at low pH (lots of H+) but loses it at higher pH. Although this may seem a slight change, it is enough to alter the wavelengths of light reflected by the compound. As a result, we see the color change with respect to pH. The lab description continues to state anthocyanins have what is seen as an opposite behavior in that the pigments gain a hydroxide (-OH) at basic pH, but lose it at acidic pH. The method provided in our lab manual will produce a visible color change in buffer solutions of known pH that will give is a standard of information to compare with a tested unknown. If the hypothesis is supported, each buffer will have a different degree or shade of