Exam 1 Flashcards Preview

Instrumental Chemistry > Exam 1 > Flashcards

Flashcards in Exam 1 Deck (88):
1

Piezoelectric Effect

The ability of certain materials to generate an electric charge in response to an applied mechanical stress

2

Refractive Index

Ratio of velocity of light to its velocity traveling thru an object/medium

3

Lock-in Amplifier

Noise reduction; recombines reference beam and sample beam after a sample has been split

4

Transmission

Light traveling through an object

5

Velocity of light is lower when.....

Traveling thru something

6

Wave Propagation

Travel/movement of waves

7

Types of Interferences

1. Constructive: increases amplitude
2. Destructive: decreases amplitude; can eliminate a wave completely at its max

8

Magnetron

Vacuum tube generates microwaves using the interaction between a string of electrons and a magnetic field, moving past a series of open metal cavities

9

Know the structure of a wave

- crest
- trough
- wavelength
- wave height

10

Types of Waves

Shortest wavelength = gamma
Longest wavelength = radio

11

Wave Trends

A. As wavelength decreases, energy increases.
B. The shorter the wavelength, the more power within a wave packet.
C. The more power within a wave packet, the greater the interaction between light and matter.

12

Electromagnetic radiation can be viewed as.....

A. Wave
B. Particle

13

Spectroscopy

The study of the interaction between electromagnetic radiation and matter.

14

Fourier transformation

Noise reduction; converts a time domain to a frequency domain

15

Calibration

Determines relationship between analytical response and analyte concentration

16

Ensemble Averaging

Data sets are averaged point by point with similar data

17

Direct Comparison

Sample that is directly compared to a primary standard; ex. Titration

18

Multivariate Calibration

Using multiple instrument responses to analyze an analyte

19

Matrix Affects

Interactions within a sample that can cause extra species in the mixture that are not found in the blank; can cause blanks to become worthless

20

Difference between a singlet and a triplet state:

A. In an excited singlet state; the electron has the same spin orientation as it had in the ground state (one arrow down, one arrow up)
B. In an excited triplet state; the promoted electron has the same spin orientation as the other electron (both arrows up)

21

When are singlet and triplet state formed?

When an electron is excited to a higher energy level.

22

Forbidden State

Spectral line associated with absorption or emission of light by an atom, which undergoes a transition that is not allowed by a transition rule.

23

The Stokes Shift

Difference between positions of the absorption and emission spectra of the same electron transition; occurs when relaxation to a lower energy excited state takes place prior to emission.

24

Advantages and Disadvantages of Inductively Coupled Plasma

Advantages:
- high limit of detection
- low chemical interference
- stable, reproducible signal

Disadvantages:
- high maintenance and operating costs
- samples must be dissolved in solution

25

Advantages and Disadvantages of Flame

Advantages:
- fast, easy to use
- inexpensive
- high precision

Disadvantages:
- large sample quantities needed
- limited to alkali and some earth metals
- issues with refractory elements

26

Electrical Domains

A. Analog
B. Time
C. Digital

27

Instrument

Converts characteristic of an analyte into information that can be interpreted

28

Basic Instrument Design

Stimulus (energy source) —> System under study —> Response

29

Transducer

Converts data from one domain to an electrical domain

30

Types of Blanks:

*used to calibrate instruments*
A. Ideal - identical to sample but withOUT analyte.
B. Solvent - contains the same solvent as the sample.
C. Reagent - contains solvent AND all reagents used in the sample preparation.

31

External Standard

Chemicals prepared separately from the standard

32

Internal Standard

Substance added in a constant amount to all samples, blanks, and calibration standards

33

What does the GC mass spec do?

detects mass to charge ratio; shows isotopes

34

About the atomic absorbable:

- linear plot obtain due to demonstration of beers law

35

If data obtained from the AA is NOT linear:

1. You could obtain more points.
2. You have maxed out the detector; dilute your samples

36

Where are vibrational states found?

Between energy levels

37

What does atomic X-ray do?

Sees what elements exist within a sample.

38

What is the most widely used technique?

AA; atomic absorbance

39

What is the AA used for?

- when looking for a metal and trying to determine concentration
- used in pharmaceutical manufacturing
- it is cheap, fast, and reliable

40

What is the atomic fluorescence used for?

Environmental applications
- lower detection limit than AA

41

What is X-ray fluorescence used for?

Rocks and minerals, steel/cement industry

42

Steps in Flame Atomization:

1. Nebulization
2. Desolvation
3. Volatilization
4. Dissociation
5. Ionization

43

Desolvation

Removal of a solvent

44

Nebulization

bulk liquid divided into drops

45

Doppler Effect

- an increase or decrease in the frequency of sound/light/etc. as the source and observer move towards or away from each other
- if it’s pointing towards you, you see the blue shift (wavelengths are at a higher energy)
- if it’s pointing away from you, you see red shift (wavelengths are at a lower energy)

46

Photomultiplier

Changes photon to electron; converting it allows it to be able to be detected by computer.

47

Band gap

Difference in energy required to move an electron between bands; difference between HOMO and LUMO

48

HOMO

highest occupied molecular orbital

49

LUMO

Lowest unoccupied molecular orbital

50

Factors of band gaps:

A. Size
B. Shape
C. Make-up (content)

51

Conductor

Electrons flow thru conduction band with out an issue

52

Semiconductor

Band gap distance can be jumped; but requires some form of energy

53

Elergy across a band gap can.....

Absorb or emit radiation (color)

54

LOOK AT QUANTUM NUMBERS

DO IT BITCH

55

Quantum Numbers:

- n
- l
- ml
- ms

56

n

gives the shell
- ex) Na = 3, Cl=3, He =1

57

l

subshells (s,p,d,f)
- values of zero to one
- s (l=0)
- p (l=1)
- d (l=2)
- f (l=3)

58

When selecting an instrument consider.....

A. Bias
B. Precision
C. Sensitivity
D. Detection Limit
E. Dynamic Range
F. Selectivity

59

Boxcar Averaging

Method of noise reduction; assumes signal varies slowly with time; average of a small number of points

60

Precision

Degree of mutual agreement of data obtained

61

Bias

Measure of systematic error

62

Sensitivity

Instruments ability to discriminate between small difference in analyte concentration.

63

Detection Limit

Minimum concentration of analyte that can be detected
*signal to noise ratio = 3:1*

64

Signal to Noise Ratio

3 to 1

65

Dynamic Range

Range of concentrations at which quantitative measurements can be obtained; distance between LOQ and LOL

66

LOQ

Limit of quantitative measurement

67

LOL

Limit of linear response

68

Selectivity

Degree to which method is free from interference by other species contained in the sample

69

Noise

Background picked up by an instrument
*always present; can be reduced.

70

Types of Noise:

A. Instrumental
B. Chemical

71

Chemical Noise

Caused by uncontrollable variables that affect the chemistry of the system being analyzed; ex. Fluctuations in temperature, pressure, humidity, light, lab fumes, etc.

72

Types of Instrumental Noise:

A. Flicker Noise
B. Shot Noise
C. Thermal (Johnson) Noise
D. Environmental Noise

73

Thermal (Johnson) Noise

Caused by thermal agitation of electrons

74

Shot Noise

Found whenever an electron crosses a junction

75

Flicker Noise

Sources not totally understood; inversely proportional to frequency (1/f)

76

Environmental Noise

Observed in different forms that originate from your surroundings; ex. Elevator, ratio, can be anything

77

Noise Reduction

A. Instrumental design
B. Grounding & shielding
C. Amplifiers
D. Analog filtering
E. Modulation
F. Synchronous demodulation
G. Lock-in amplifier
H. Software methods (ensemble averaging, boxcar averaging, Fourier transformation)

78

Raman Scatterings

Scattering of light where wavelength is changed

79

Mie Scatterings

- Scattering of molecules that are larger than the wavelength
- ex. Why the clouds are white

80

Rayleigh Scattering

- Scattering of molecules that are smaller than the wavelength of radiation
- ex. Why the sky is blue

81

Scattering

Change in the direction of a vector; small portion of incident light hits destructive interfaces and light is transmitted at all angles from original path.

82

Reflection

Occurs when light cross an interface between media that differ in refraction index.
Ex. Puddle in middle of road; mirage

83

Spectroscopy

Study of interaction of electromagnetic radiation (light) and matter.

84

Volatilization

Process where a dissolved sample is vaporized

85

Dissociation

The splitting of a molecules into smaller molecules or atoms

86

Ionization

Process by which an atom or molecules obtains a positive/negative charge due to the loss/gain of electrons

87

Quant Number ml

Indicates the energy shift; position in sub shell where electron resides.
S (1 spot)
P (3 spots)
D (5 spots)
F (7 spots)
Negative to positive

88

Quantum Number ms

Spin on electron