How do you determine pk of indicator by spectrophotometry

Answer 1

To determine the pK of an indicator by spectrophotometry, you can follow these steps:

1. Prepare a series of buffer solutions with different pH values covering the range of interest (usually around the expected pK of the indicator).

2. Add the indicator to each buffer solution and measure the absorbance of the solution at the indicator's absorption maximum using a spectrophotometer.

3. Plot a graph of absorbance versus pH for each buffer solution.

4. From the graph, identify the point at which the absorbance of the solution is equal to 50% of the maximum absorbance (corresponding to a ratio of protonated and deprotonated indicator species of 1:1). This pH value corresponds to the pK of the indicator.

5. Repeat the experiment to ensure accuracy and obtain an average pK value.

By following these steps, you can determine the pK of an indicator using spectrophotometry.