EMR/UV-Vis

Question 1

Light waves are electromagnetic. True or false?

Answer 1

True

Question 2

How is the speed of light calculated?

Answer 2

Wavelength x frequency

Question 3

On absorption of radiation, electrons are promoted from a low energy state to a higher energy (excited state). True or false?

Answer 3

True

Question 4

EMR is produced when excited particles return to lower-energy levels or the ground state. True or false?

Answer 4

True

Question 5

Excitation of a molecule can be electronic, rotational or vibrational. True or false?

Answer 5

True

Question 6

What is on the y and x axis of UV-Vis spectrums?

Answer 6

y - absorbance

x - wavelength

Question 7

Most drugs, with the exception of _______ ones absorb UV light

Answer 7

coloured

Question 8

Why is the UV-vis spectrum broad rather than sharp?

Answer 8

Because photons with slight difference in energy can still cause electronic transitions from exciting electrons from the many vibrational states

Question 9

What are the three types of orbitals?

Answer 9

sigma
pi
n - non-bonding

Question 10

When a bonding orbital is created, there is also an anti-bonding orbital created that is normally unoccupied but lies at a higher or lower state?

Answer 10

Higher (less stable) state

Question 11

On energy level diagram, jumps from which two states are in low enough energy for pharmaceutical analysis?

Answer 11

pi to pi*

and n to pi*

Question 12

> 200nm absorption is most common for pharmaceutical analysis. True or false?

Answer 12

True

Question 13

What are the 3 uses of UV absorption?

Answer 13

Identification of drugs - by comparing spectra
Measuring reactions, ionisation
Quantification of drugs - most useful

Question 14

UV absorption is mostly restricted to drug molecules with conjugated bonds. True or false?

Answer 14

True

Question 15

What is meant by a conjugated structure?

Answer 15

Double bonds alternating with single bonds

Question 16

Conjugated structures tend to shift absorption to a shorter wavelength. True or false?

Answer 16

False - longer wavelength

Question 17

What is meant by a bathochromic shift?

Answer 17

shift to a longer wavelength

Question 18

The longer the conjugated system, the less separation in energy levels and therefore the longer the wavelength. True or false?

Answer 18

True

Question 19

Bathochromic is a red shift. True or false?

Answer 19

True

Question 20

What colour is associated with a hypsochromic shift?

Answer 20

Blue

Question 21

Why does conjugation shift the wavelength to red?

Answer 21

Because in conjugated systems, electrons are easily delocalised, making energy gaps between orbitals smaller, therefore lowering the energy needed to excite them

Question 22

What is an auxochrome?

Answer 22

A functional group containing lone pair(s) of electrons that do not absorb appreciable amounts of UV on its own but shifts peaks to longer wavelength and makes the peak higher intensity

Question 23

What is a chromophore?

Answer 23

Part of the molecule that absorbs UV or visible light

Question 24

The amount of light absorbed is dependent on the concentration of a sample. True or false?

Answer 24

True

Question 25

What is the equation for the Beer lambert law?

Answer 25

A = Ebc 
E = molar absorptivity (absorbance of 1M solution)
b = path length of cell in cm
c = conc in mol/l

Question 26

What does the beer lambert law apply?

Answer 26

A linear relationshop between absorbance and concentration. However, in reality, this is only true if A > 1.5

Question 27

In the beer lambert law, what assumptions apply for absorbance to be directly proportional to concentration?

Answer 27

Incidence radiation must be monochromatic
absorbance checks can be made against standards such as potassium dichromate
each molecule in solution acts as an independent absorbing species
absorption takes place in a homogenous solution