Ph Buffer Using Cabbage Indicator

981 Words4 Pages
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
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Acids were varying shades of red or pink and the bases were varying shades of green. The only unexpected result was the variability of color change in the pH 12 buffer solution, though this was attributed to the text, Table 2, stating the pigments are not stable at pH 12 (Pearson, 37). A weakness of using red cabbage indicator to check the pH of an unknown solution or buffer is the subjectivity of determining color. What one individual sees as pink. another person would see as light purple. Color blind individuals would be at a significant disadvantage. Accuracy of pH is another consideration, since in addition to the variability in shades of color the pH shown by the red cabbage indicator is more of a ballpark estimate and limited to whole numbers. Using a pH meter, we can get a significantly more accurate reading that is objective and not dependent on an individual's interpretation of color or visible hue. In addition to the subjectivity of color, one would need to ensure a consistent ration of indicator solution to test solution in order to not affect the shade of the color change. Based on the data received and background information given, it is my opinion that although red cabbage indicator solution can be used to determine pH levels, it is best used as a more general indicator of whether a solution is an acid, base or neutral.

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