Plant Pigments and Ph - Bio 251 Lab 1

Plant Pigments and pH

Table 1
Absorbance of red cabbage anthocyanin at various pH values , and unknowns 1 and 2. |
pH | color | 400 | 450 | 500 | 550 | 600 | 650 |
pH 2 | red | 0.096 | 0.115 | 0.359 | 0.195 | 0.006 | 0.002 |
pH 3 | pink | 0.06 | 0.05 | 0.117 | 0.091 | 0.023 | 0.007 |
pH 5 | fuchsia | 0.1 | 0.023 | 0.073 | 0.071 | 0.04 | 0.01 |
pH 7 | purple | 0.189 | 0.034 | 0.074 | 0.092 | 0.099 | 0.04 |
pH 8 |   aqua | 0.268 | 0.051 | 0.069 | 0.061 | 0.083 | 0.032 |
T1 |   aqua | 0.302 | 0.056 | 0.028 | 0.071 | 0.109 | 0.251 |
T2 |   pink | 0.039 | 0.034 | 0.163 | 0.127 | 0.002 | 0 |

Table 2
Transmittance (%) of red cabbage anthocyanin at various pH values, and unknowns 1 and 2 |
pH | 400 | 450 | 500 | 550 | 600 | 650 |
pH 2 | 80.4 | 76.8 | 43.8 | 63.8 | 98.6 | 99.6 |
pH 3 | 87 | 89.2 | 76.4 | 81 | 94.8 | 98.4 |
pH 5 | 79.4 | 95 | 84.6 | 84.8 | 91.2 | 97.6 |
pH 7 | 64.8 | 92.6 | 84.2 | 81 | 79.6 | 94.2 |
pH 8 | 54 | 89 | 85.2 | 86.8 | 82.6 | 93.8 |
T1 | 50 | 88 | 93.8 | 84.8 | 77.8 | 56 |
T2 | 91.4 | 92.2 | 68.6 | 74.6 | 99.6 | 100 |

Based on your results what are the approximate pH values for your Test solutions?
Test #1: | Test #2: |
pH= 8 | pH = 3 |

Give supporting data for the proposed pH values in the form of two graphs. Compare the data for the test solutions with the data for the known pH solutions. One graph should be for absorbance and the other should be for transmittance.


Lab write-up questions
  1. Write the equilibrium reaction for the ionization (dissociation) of water. What is the pH of pure water? What is the concentration of H+ in pure water?

The equilibrium reaction for the ionization of water is:
H2O↔H++HO-   or   H2OH2O+↔H3O++HO-
The pH of pure water is approximately 7. The concentration of H+ in pure water is approximately 10-7 M Hydrogen ions in solution.

  2. Which solution has a higher H+ concentration: one with pH 12 or one with pH 3? How do you know this?

The solution... [continues]

Read full essay