spectrophotometry
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Beer-Lamber law
The fraction of light absorbed by the sample is directly proportional to the number of molecules in the path length
Outline method of determination of pKa
• determine λ max of substance in its ionised & unionised form. • use these as λ1 and λ2. • determine the absorption coefficient for each of these at λmax. • treat the solution of the unknown substance as a mixture of ionised and unionied material • Measure the absorption at λ1 and λ2 • Determine the conc of ionised & unionised material present using the method of simultaneous equation. • Use these values and the pH to solve the Henderson-Hasselbach equation to calculate the pKa.
what happen when molecules are excited by microwave?
they rotate
what happen when molecules are excited by infrared?
they rotate and vibrate
what happen when molecules are excited by visible light?
they rotate, vibrate and undergo electron transition
what happen when molecules are excited by UV light
they rotate, vibrate and undergo electron transition
Infra red spectroscopy
• range 4000-625cm-1 • aka vibration spectroscopy • measures rotation and vibration of molecule • tells s about individual bonds ie functional group
types of absorption
• rotation • vibration • electron transition
Uv spectroscopy
• range 200-750nm • causes excitation in the bond • also changes in vibrational and rotational energies • used to determine concentration in solution