spectrophotometry Flashcards
1
Q
Beer-Lamber law
A
The fraction of light absorbed by the sample is directly proportional to the number of molecules in the path length
2
Q
Outline method of determination of pKa
A
- 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.
3
Q
what happen when molecules are excited by microwave?
A
they rotate
4
Q
what happen when molecules are excited by infrared?
A
they rotate and vibrate
5
Q
what happen when molecules are excited by visible light?
A
they rotate, vibrate and undergo electron transition
6
Q
what happen when molecules are excited by UV light
A
they rotate, vibrate and undergo electron transition
7
Q
Infra red spectroscopy
A
- range 4000-625cm-1
- aka vibration spectroscopy
- measures rotation and vibration of molecule
- tells s about individual bonds ie functional group
8
Q
types of absorption
A
- rotation
- vibration
- electron transition
9
Q
Uv spectroscopy
A
- range 200-750nm
- causes excitation in the bond
- also changes in vibrational and rotational energies
- used to determine concentration in solution
