Essay about Ph Buffer Using Cabbage Indicator
NB 1110 / M 5 – 7:50
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 …show more content…
Procedure: Seven clean glass test tubes were placed in a test tube holder, then labeled 2, 4, 6, 8, 10, and 12 using marker on tape to correspond to the appropriate pH buffer solution that would be used. Buffer of pH 7 was not provided. Next, 5 mL of buffer solution was placed in the corresponding test tube (i.e. buffer of pH 6 placed in tube labeled 6, and so on), using a new disposable pipet for each to ensure buffers were not affected by cross contamination. We then used a glass dropper bottle of cabbage extract provided by the instructor and added 3 mL of cabbage extract to Tube 2, then covered with parafilm before mixing the buffer and extract. Color change was documented. These steps were repeated for all buffers.
Results Acidic buffers turned varying shades of red, while the alkaline buffers changed to varying shades of green.
Table 1 Color of Standard Solutions for Red Cabbage Indicator Buffer pH | Final Color | 2 | Bright pink | 4 | Soft purple/pink | 6 | Light purple | 7 | Not provided | 8 | Blue-green | 10 | Dirty green | 12 | Green progressing to violet |
Discussion The hypothesis that red cabbage indicator solution can be used as an indicator of