Mass Spectroscopy

Question 1

what is spectroscopy?

Answer 1

spectroscopy is a non-destructive analysis technique where electromagnetic radiation is passed through a substance to analyze it

Question 2

what is electromagnetic radiation?

Answer 2

EMR is energy that travels in wave motion and can pass through a vacuum. It includes gamma rays, X-rays, UV light, visible light, infrared, microwaves, and radio waves.

Question 3

what is the relationship between wavelength, frequency and velocity of EMR?

Answer 3

Velocity of a wave is the product of its wavelength and frequency : . For EMR, (speed of light).

Question 4

what are the types of spectrums in spectroscopy?

Answer 4

1. Emission Spectrum: Energy emitted by excited molecules analyzed by a spectrometer.
2. Absorption Spectrum: Energy absorbed, reflected, and transmitted analyzed by a spectrometer.

Question 5

what are the types of spectrums in spectroscopy?

Answer 5

1. Emission Spectrum: Energy emitted by excited molecules analyzed by a spectrometer.
2. Absorption Spectrum: Energy absorbed, reflected, and transmitted analyzed by a spectrometer.

Question 6

what is ultraviolet spectroscopy?

Answer 6

It involves the absorption of UV light by molecules, causing electron transitions between bonding and anti-bonding orbitals.

Question 7

what are chromophores?

Answer 7

Chromophores are structural features of a compound that absorb UV energy at specific wavelengths, helping in identification.

Question 8

state Beer-Lambert’s law

Answer 8

The extent of UV light absorption is proportional to the concentration and path length of the sample: , where is the molar absorptivity constant.

Question 9

what is conjugation in spectroscopy?

Answer 9

Conjugation refers to delocalization in alternating single and double bonds, reducing the energy needed for transitions, leading to absorption in the visible spectrum.

Question 10

what are the major uses ofUV spectroscopy

Answer 10

1. Detecting chromophores.
2. Measuring concentrations of substances (e.g., glucose in blood).
3. Analyzing pollutants or substances in water.

Question 11

what are the two types of molecular variations in IR spectroscopy?

Answer 11

1. Stretching vibrations: Rhythmic changes in bond lengths.
2. Bending vibrations: Changes in bond angles.

Question 12

what is the significance of the fingerprint region in IR spectroscopy?

Answer 12

the fingerprint region is unique to each compound, aiding in its identifiation

Question 13

what is the significance of the fingerprint region in IR spectroscopy?

Answer 13

the fingerprint region is unique to each compound, aiding in its identifiation

Question 14

what materials are used in IR sample preparation and why?

Answer 14

NaCl or KBr is used since they do not absorb IR radiation, ensuring 100% transmission through the sample.

Question 15

list some uses of IR spectroscopy

Answer 15

1. Identifying functional groups.
2. Forensic analysis.
3. Monitoring atmospheric pollutants.
4. Breathalyzer tests.

Question 16

how do you prepare a solid sample

Answer 16

1. Add a few drops of the oily liquid (nujol) and make into a mull.
2. The mull is then placed between a pair of discs made of KBr or NaCl.
3. The discs are then placed in the IR spectrometer and absorbance is measured

Question 17

how to prepare a liquid sample?

Answer 17

Place a few drops of the liquid between a pair of discs made from NaCl or KBr

Question 18

how to prepare a gas sample?

Answer 18

Place the gas in a cell 10cm wide. The walls of the cell are made from NaCl or KBr

Question 19

describe the bond spotting region

Answer 19

(4000 cm-1- 1200 cm-1)- in this region, there are few peaks and isused to identify the bonds and the functional group in a compound.

Question 20

describe the bond spotting region

Answer 20

(4000 cm-1- 1200 cm-1)- in this region, there are few peaks and isused to identify the bonds and the functional group in a compound.

Question 21

condition for IR to be absorbed

Answer 21

the molecule must possess a dipole or the vibration mustcause a change in the dipole moment.Symmetrical diatomic molecules will not absorb IR radiation.

Question 22

role of a complexing agent

Answer 22

If a substance does not absorb light in the UV visible part of the spectrum, it can be made to absorb by adding a complexing agent.
The complexing agent reacts with the substance to produce a particle which absorbs (ex. Add potassium thiocyanate to make Fe2+ absorb).

Question 23

uses of a complexing agent

Answer 23

To detect the presence of chromophores in the substance

To obtain the concentrations of dilute solutions by measuring absorbance

Question 24

what is a calibation curve?

Answer 24

A calibration curve is a plot of absorbance against concentration for a sample. This curve is veryuseful to determine the concentration of a solution by measuring its absorbance.

Question 25

assumptions of Beer Lambert’s Law

Answer 25

1. The light passing through the substance must be monochromatic ie. UV light of a singlewavelength.
2. The absorption process must take place in a volume over a uniform area.
3. The substance which is absorbing must behave independent of the solvent used.
4. This law is generally obeyed by dilute solutions.

Question 26

Beer Lambert equation

Answer 26

A= molar absorptivity constant x concentration x wavelength

Question 27

transitions from ultraviolet light

Answer 27

π → π#
n → π#
n → σ#

Question 28

orbitals formed during overlapping of two orbitals

Answer 28

bonding molecular orbital
anti-bonding molecular orbital

Question 29

equation for energy using Planck’s constant

Answer 29

𝐸 = ℎ𝑓
𝐸 = ℎ𝑐 / λ