UV Vis

Question 1

What does UV Vis spectroscopy help with?

Answer 1

It helps us figure out the concentration of the solution

Question 2

Describe a UV Vis Spectrophotometer.

Answer 2

Source of light (UV or Vis light), Entrance Slit, Dispersion Device (monochrometer), Exit Slit, Sample (Qvet could be made of plastic or quartz), Detector

Question 3

What range of wavelength of light is a UV Vis done?

Answer 3

200-800 nm

Question 4

What is the name of the molecule put in the sample?

Answer 4

Analyte

Question 5

Percent Transmittance Equation

Answer 5

%T = (Idetector/ Isource) x100

Question 6

Absorbance Equation

Answer 6

A = -log(Idetector/Isource)

2 - log(%T)

Question 7

Explain Beer-Lamber Law? (Beer’s Law)

Answer 7

A = epsilon x length x concentration

concentration - affects how much light is absorbed

length - path length (how much length light travels)

Molar absorptivity, epsilon - the probability that the sample will absorb light

Question 8

What is the wavelength that absorbs the most light called?

Answer 8

lambda max

Question 9

What are the effects of structure on Lambda Max?

Answer 9

Molecules that contain only sigma bonds do NOT absorb UV or Visible light regions, their Lambda Max is too short

Molecules that contain at least 1 pi bond have a lambda max greater than about 160 nm

As the amount of conjugation increases, the lambda max gets larger

Question 10

Why does conjugation cause a higher wavelength?

Answer 10

as you increase the amount of conjugation, the HOMO LUMO gap decreases

wavelength decreases
frequency increases
energy of a photon increases