# Phenolphathalein 2019.04.10

Kinetic of degradation of phenolphthalein in basic media works well as shown in the previous experiment.

## Goal

We want to measure the order of the reaction. In the literature, it is told that you are expected to use constant ionic force. But is this necessary ?

Let's check if we replace NaCl 0.3M by water to see if it yields to the same result.

## Solutions

- solution A: NaOH 0.3M in water
- solution B: water
- solution C: phenolphthalein 3.02 g/L in MeOH / EtOH

Experiment | A | B | C |
---|---|---|---|

1 | 4 mL | 0 mL | 40 µL |

2 | 3 mL | 1 mL | 20 µL |

3 | 2 mL | 2 mL | 20 µL |

4 | 1 mL | 3 mL | 20 µL |

## Results

Raw data for the 4 kinetics are attached in the corresponding documents:

The data were processed online on the following page.

An exponential regression has been applied for the 4 experiments for all the points having an absorbance over 0.3 and the following results are observed:

Experiment | [NaOH] | k | r^{2} |
---|---|---|---|

1 | 0.300 M | 0.2878 | 0.99997 |

2 | 0.225 M | 0.1984 | 0.99998 |

3 | 0.150 M | 0.1217 | 0.99997 |

4 | 0.075 M | 0.0460 | 0.99959 |

## What is r^{2} ???

## NaOH regression

- y = −0.03705 + 1.069 x
- r
^{2}= 0.9983

Even without constant ionic strength the results are still quite good. The slope is close to 1 despite the fact that it is far from passing through 0,0.