Atomic Spectroscopy

Question 1

What spectrum does visible light belong too?

Answer 1

Electromagnetic radiation

Question 2

What is an oscillation?

Answer 2

An oscillation is a wave like property that occurs in regular variations.

Question 3

What is frequency?

Answer 3

Frequency is how many times the wave crests per second.

Question 4

What is frequency measured in?

Answer 4

Hertz (Hz) with a unit of reciprocal seconds

Question 5

What is a wavelength?

Answer 5

A wavelength is the distance between two crests of a oscillation. Wavelength is denoted by Lambda λ and is measured in meters.

Question 6

What does the product of wavelength and frequency produce?

Answer 6

The speed of light (C (ms-1)).

Question 7

If speed of light is constant in a vacuum, what does that imply about the relationship between wavelength and frequency?

Answer 7

That they are inversely proportional.

Question 8

What is amplitude?

Answer 8

Amplitude is the displacement of the wave from the central point, therefor it is half of the total movement.

Question 9

What property is amplitude responsible for in light?

Answer 9

It is responsible for the intensity of a light, not to be confused with energy of light. Higher amplitude = brighter light.

Question 10

How do we calculate the energy of a wavelength?

Answer 10

To get the energy of a wavelength with multiply Planck’s constant (h) by the frequency of the wave (v) . E = h v

Question 11

What is Planck’s constant and its unit?

Answer 11

Planck’s constant is 6.626 x 10-(34) and it is measured in Joules per second.

Question 12

How do we get the unit of energy using E = h v?

Answer 12

If h is joules per second and frequency is measured in reciprocal seconds then we get E = Joules.

Question 13

How does an increase of frequency appear on the electromagnetic spectrum?

Answer 13

An increase in frequency will correspond to a shorter wavelength and a higher energy. Higher frequency will move towards gamma rays, whilst lower frequency will move towards radio waves.

Question 14

What is a broadband?

Answer 14

It is the collection of a range of frequencies. An example would be white light which is a collection of all visible light spectra.

Question 15

What are the two possible effects that the absorption of energy can have on electrons?

Answer 15

Ionisation and Transition.
Ionisation is when a large enough energy can completely dissociate an electron from a nucleus. Transition is where a smaller energy is absorbed by the electron and it is transitioned into a higher state.

Question 16

What is common in excited electrons?

Answer 16

These electrons will readily give up their excess energy so that they can fall back down to ground state.

Question 17

How can an electron lose its excess energy?

Answer 17

It can either emit light (Fluorescence) or it can lose it in collisions to other molecules/atoms (Heat).

Question 18

What is a fluorescent material?

Answer 18

It is a material that can absorb higher energy UV light and then re emit at a lower frequency which is the visible light.

Question 19

How do we get an absorption spectrum?

Answer 19

We get it by subjecting a gas substance of interest with a full visible light broadband. The resulting black marks on a spectroscope determines the frequencies absorbed.

Question 20

what is an emission spectrum?

Answer 20

It is when a gas discharge tube excites a gas of interest in a visible light absent environment. by passing the emitted light discharge through a prism we can determine the frequencies released.

Question 21

Why is absorption and emission spectra useful?

Answer 21

Because each element has its own unique frequency characteristics which can then help with identification.

Question 22

Why is the emission and absorption spectra of atoms quantised?

Answer 22

As the spectra can only have absolute specific values. This is because the electrons are restricted to specific energy states.

Question 23

How many electrons can an orbital accomodate?

Answer 23

An orbital can either contain 0 , 1 or 2 Orbitals.

Question 24

What does orbitals have to do with absorption and emission spectra?

Answer 24

Orbitals are the quantised energy levels that predefined how electrons get excited or emit. When an electron is excited it gets promoted to a higher orbital and vice versa.

Question 25

What is a limitation of Atomic Absorption/Emission Spectroscopy?

Answer 25

It is fairly limited to atoms, as molecules are too complex. It is generally reserved for trace elements.

Question 26

In terms of data, does AAS or AES provide more data points?

Answer 26

Atomic emission spectroscopy provides more data as the emission pathway between orbitals has a greater variation the the absorption spectroscopy. More Data lines is AES.

Question 27

How do we using atomic spectroscopy on elements that have combined with others?

Answer 27

We use atomisation to destroy any molecules and leave nothing but elements to be used in spectroscopy.

Question 28

What are the steps of flame AAS?

Answer 28

1) Prepare a solution using a solvent. (Typically Water)
2) Nebulise the solution into tiny droplets
3) Desolvation to evaporate the solvent
4) vaporisation of the compound to produce a gas
5) atomisation of the gas to product a neutrally charged atom.
6) the excitation of the analyte

Question 29

How do we interpret data from flame AAS?

Answer 29

Flame AAS measures the quantity of analyte present by investigating the decrease of intensity of light. This is measured by passing light through the analyte flame.

Question 30

How do we ensure that we are measuring the correct element?

Answer 30

We only use wavelengths specific to the elements absorption band as a light source.

Question 31

how do we ensure that a specific light wavelength is used as the incident light on the flame in flame AAS?

Answer 31

We use a monochromator to filter out unwanted wavelengths.

Question 32

What does beer-lamberts law suggest in regards to flame AAS?

Answer 32

That the comparison of incident light to the absorbed light can determine the quantity of analyte.

Question 33

What is beer lamberts law?

Answer 33

Absorbance = Log( Incident Light / After Incident Light) = Molar absorbity x Path length of flame x concentration of analyte

A = Log( Io / I ) = abc

Question 34

What is electrothermal AAS?

Answer 34

Electrothermal AAS is the same as flame AAS, however instead of using flame, heat is generated electrically in increasing stages. These increase until the element analyte is released into a gas form.

Question 35

What is the advantage of electrothermal AAS?

Answer 35

It allows form any state of analyte to be tested (Solid, liquid, Gas)

Question 36

what is the disadvantage of electrothermal AAS?

Answer 36

Higher costs and lower throughputs.

Question 37

In order to confirm the accuracy of aborbance measures what do we need to do?

Answer 37

We need to create a calibration curve that allows us to compare where Beer-lambert law remains linear. By using the calibration curve we can dilute our analyte if necessary to ensure we are getting an accurate reading.

Question 38

What maximum value of absorbance should we take as accurate?

Answer 38

An absorbance value of 1.5

Question 39

What is ICP-OES

Answer 39

This is Ion coupled plasma spectroscopy.
By using a argon based plasma as a excitation source we can near completely atomise the analyte which will give a more accurate result.

Question 40

What are some practical considerations of spectroscopy?

Answer 40

AS we are measuring for trace elements it is essential that we use analytical grade chemicals and reagent blanks in our research.
As there is many factors that can affect the analysis from atomisation, nebulisation, flame, etc. we need to run frequent standards.