Principle
For weak acids HA, the position of the Ka and
pKa values that characterise the dissociation
equilibrium in the ground state can be determined from photometric
measurements in solutions having different pH values. Further to
this, the pKa* value for the excited state is accessible
from the spectrophotometric data.
Benefits
- Modern spectrophotometer with display
- Spectrophotometer can be used for many other applications
- Detailed operating instructions
Tasks
- Record near UV absorption spectra of p-methoxyphenol in dilute
HCl, NaOH and 5 different borate buffer solutions of known pH.
- Calculate the pKa and pKa* values for the
system.
What you can learn about
- Ground and excitation states of molecules
- Electron excitation spectroscopy (UV-VIS spectroscopy)
- Spectroscopical energy and adsorption measurement
- Jablonski diagram and Foerster cycle
- pKa and pKa* values
- Henderson-Hasselbalch equation
- Van't Hoff's reaction isotherms
- Gibbs-Helmholtz equation
- Lambert-Beer law
- Photometry