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5) Analytical Chemistry > UNIT4 Spectroscopy (edit!) > Flashcards

UNIT4 Spectroscopy (edit!) Flashcards

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1
Q

What is spectroscopy?

A

Interactions of readiation and matter

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2
Q

How is spectroscopic analysis measured?

A

Amount of radiatio produced or absorbed

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3
Q

What waves are used?

A

γ-ray, X-ray, ultraviolet (UV), visible, infrared (IR), microwave, and radio-frequency (RF)
ALSO acoustic, massm electron spectroscopy

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4
Q

What is the most widely used method?

A

elucidation of molecular structure and quantitative and qualitative determination

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5
Q

What is electromagnetic radiation?

A

Wave with properties of a wavelength, frequency, velocity and amplitude

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6
Q

What medium of transport does electromagnetic radiation use?

A

No medium

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7
Q

How can electromagnetic radiation be seen?

A

discrete packets of energy paticles —> photons or quanta

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8
Q

What is the energy of the photon?

A

Proportional to its frequency

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9
Q

How is electromagnetic radiation modeled?

A

Waves consisting of perpendicularly oscillating electric and magnetic feild

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10
Q

Amplitude

A

Strength at a maximum in a wave

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11
Q

Period (p)

A

time in seconds for successive maxima and minima to pass a point in space

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12
Q

Frequency v

A

number of oscillations that occur in one second –> 1/p

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13
Q

What is the unit of frequency?

A

Hertz (Hz)

One cycle per second

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14
Q

What is the wavelength?

A

Linear distance between sucessive maxima or minima

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15
Q

Velocity

A

speed that depends on the medium and frequency

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16
Q

Is the frequency or velocity constant?

A

Frequency

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17
Q

What is wave number

A

Way to describe electromagntic radiation –> number of waves per centimeter = 1/λ

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18
Q

What is a photon?

A

Particle of electromagnetic radiation having zero mass and an energy of hv

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19
Q

What is the equation for wavenumber?

A

E=hv=hc/λ=hcv~

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20
Q

What is plank’s constant?

A

6.63*10^-34J

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21
Q

What are the most important interactions in spectroscopy

A

transitions between different E levels

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22
Q

Visible light spectrum

A

380-780

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23
Q

What is visible spectrum

A

180-380nm

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24
Q

What is another word to spectrochemical methods?

A

OPtical methods, even when you cannot see some of them

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25
Q

How do you begin a spectroscopic method?

A

Sample is stimulated by applying energy (heat, electirc, light, particles

26
Q

What is the state of the analyte before the stimulus?

A

Lowest- energy / ground state

27
Q

Why is the analyte in the ground state?

A

In order to transition to a higher more excited state

28
Q

How do we acquire information about the analyte?

A

Measure the electromagnetic readiation emitted or the amount of electromagnetic readiation absorbed

29
Q

The results of spectroscopy is expressed by…

A

Graphically by a spectrum –> plot of emitted/absorbed radiation as a function of frequency, wavelength or wavenumber

30
Q

Emission spectroscopy?

A

Methods which the stimulus is heat or electrical

31
Q

Chemiluminescence spectroscopy?

A

Excitation of analyte by chemical reaction

32
Q

Absorption spectroscopy

A

light absorbed as a function of wavelength

33
Q

photoluminesence spectroscopy

A

emission of photon measured following absorption

34
Q

What are the most important forms of photoluminescence?

A

Fluorensence and phosphorescence

35
Q

Every molecule is able of absorbing….

A

its own characteristic frequencies of elec radiation

36
Q

What is the process of absorption of radiation?

A

Transfer energy to the molecule and results in a decrease in intensity of incident

37
Q

What happens to the beam in absorption of radiation?

A

Attenuates the beam in accordance to the Beer-Lambert Law

38
Q

What is Beer’s Law

A

Amount of attenuation depends on the concentration of absorbing moleules and the path length

39
Q

According to Beer’s Law, the longer the length of the medium?

A

The greater attenuation

40
Q

According to Beer’s Law, the higher the concentration of absorbers

A

The stronger the attenuation

41
Q

What is the transmittance

A

the fraction of incident radiation transmitted by the solution
T=P/P0

42
Q

Absorbance as a solution is denoted as

A

A=-logT=-log%T+log100=2-log%t

43
Q

What happens with radiation at the cell wall

A

Reflection and scattering losses

–> can be substantial

44
Q

How do we compensate for the scattering losses?

A

Reagent blank

45
Q

What is absorbance according to Beer’s Law?

A

Absorbance is directly proportional t the concentration of the absorbing species c and to the path length c
A=Ebc
E–> absorptivity in L mol^-1 cm^-1

46
Q

Why are high molar absorptivities good?

A

high analytical sensitivity

47
Q

The longer the path length, the _____ the attenuation

A

Greater

48
Q

As absorbance increases, transmittance ____

A

decreases

49
Q

The study of the interaction between electromagnetic radiation and matter is…

A

Spectroscopy

50
Q

Electromagnetic radiation is modeled as a ____ to explain different phenomena such as reflection, refraction, interference and diffraction

A

wave

51
Q

When an excited chemical molecule returns to its ground state it ___ energy

A

emits

52
Q

A plot of the emitted or absorbed radiation as a function of frequency, wavelength or wavenumber is ____

A

Spectrum

53
Q

Beer’s law relates the __ of the electromagnetic beam to the path length and the concentration of absorbing species

A

attenuation

54
Q

True or false: the attenuation of the electromagnetic beam results only from molecules absorbing electromagnetic energy

A

False

55
Q

Vibration of chemical bounds is induced by ___

A

Infrared light

56
Q

True or false: IR radiation causes transitions in the electronic, vibrational and rotational states.

A

False. Only in the rotational and vibrational states

57
Q

Total energy in atomic and molecular absorption is a sum of what energies?

A

electronic, vibrational and rotational

58
Q

What do the spectra of liquid, gas, nonpolar and polar states look like?

A

gas: many peaks resulting from transitions
liquid & non polar solvents: no fine structure, plus still peaks
polar solvents: band becomes blurred

59
Q

Why do polar solvent have a blurred spectrum?

A

Because collisions between particles tend to spread energies of quantum states and the spectrum appears as a single broad peak

60
Q

Beer’s law only applies to what type of solutions?

A

Dilute

61
Q

Name some instrumental deviations to Beer’s law?

A
  • Measurements must be made with monochromatic source radiation
  • Polychromatic sources must be used with a filter to isolate band
  • Stray radiation/light: result of scattering and reflection
  • mismatched cells (intercept k will appear in calibration curve)
62
Q

Name a chemical deviation to Beer’s Law

A

Absorbing species dissociates, associates or reacts with solvent to give a product that absorbs differently

5) Analytical Chemistry (11 decks)

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