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Instrumental Analysis > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

What is the wave model of light?

A

Electromagnetic waves propagate with an electric field perpendicular to the magnetic field where both oscillate perpendicular to the direction of propagation

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2
Q

What is the equation for frequency?

A

1/T

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3
Q

What is the equation for speed of light in terms of wavelength and frequency?

A

lambda*mu = c

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4
Q

the frequency of the light is invariant and is dependent on the source

A

wave model of light

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5
Q

the speed of light depends on the medium through which is travels

A

wave model of light

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6
Q

what is the index of refraction?

A

The index of refraction of the medium is the ratio of the speed of light in vacuum to the speed of light in the medium

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7
Q

orientation of the electric field determines the polarization of the electromagnetic wave

A

linear polarization/plane polarization

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8
Q

only allows one plane of polarization to pass through

A

polarizer

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9
Q

What is the double-slit experiment?

A

When light passes through two closely spaced slits, an interference pattern is produced.

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10
Q

a result of adding waves that are in phase

A

constructive interference

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11
Q

a result of adding waves that are out of phase

A

destructive waves

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12
Q

how do you describe the interaction of matter with light?

A

interaction of irradiation with matter. refer to the light as photons

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13
Q

what is the energy of one quanta of light?

A

E=hv

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14
Q

molecules may exist in discrete energy states called…

A

steady states

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15
Q

do atoms have vibrational and rotational energy?

A

no, only molecules

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16
Q

lowest energy state

A

ground state

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17
Q

__________ produced in the UV and visible region of the spectrum when the radiating species are individual atomic particles that are well separated in the gas phase

A

line spectra

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18
Q

_____ determines the distribution of molecules populating an excited state over a ground state

A

boltzmann distribution

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19
Q

as the fraction of molecules populating the excited state increases…

A

absorbance intensity decreases

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20
Q

the frequencies absorbed by atoms and molecules are characteristic of…

A

the molecule and its interaction with the solvent

21
Q

The many discrete peaks in the
absorption spectrum come from excitation from the ground vibrational state to excited vibrational states in the excited electronic state.

A

vibrational fine structure

22
Q

uncertainty principle: the shorter the lifetime…

A

the broader the band. things that shorten the lifetime include collisions with solvent or solute

23
Q

how is transmittance defined?

A

power incident divided by transmitted power

24
Q

how is absorbance defined?

A

-logT

25
Q

Beer-Lambert law

A

absorbance is proportional to the thickness of the sample, the concentration and a property inherent to the sample, the molar absorptivity

26
Q

how close our instrument comes to measuring a “true value”

A

accuracy

27
Q

how do you calibrate an instrument?

A

take the mean of several measurements

28
Q

For addition and subtraction the final error is just the square
root of the sum of errors squared, while for multiplication and
division the relative error of the final calculation is the square root of the sum of relative errors squared. The relative error is just the error divided by the mean.

A

propagation of error

29
Q

What is a null hypothesis

A

there is no difference between the two samples

30
Q

determines if the standard deviations of the two distributions differ significantly from one another

A

F test

31
Q

determines if the means of samples are different

A

t test (two means), ANOVA (multiple means)

32
Q

what are the typical spectroscopic instrument components?

A
  1. Source lamp/heated solid
  2. sample holder
  3. wavelength selector
    4.photoelectric transducer
  4. signal processor and readout
33
Q

______ emits radiation over a broad range of wavelengths, with a relatively smooth variation in intensity

A

continuum source

34
Q

_______ emits radiation at discrete wavelengths, with broad regions showing no emission lines

A

line source

35
Q

What are examples of continuum sources?

A

Deuterium lamp - UV range
tungsten lamps - UV to Near IR
argon lamp - VAC
nernst glower - UV- Far IR
nichrome wire - Near IR - far IR
globar Near IR- Far IR

36
Q

What are examples of line sources?

A

hollow cathode lamps - UV - Visible
lasers - VAC - IR

37
Q

what does a narrow bandwidth do for measurements?

A

enhances sensitivity of absorbance and provides selectivity for absorption and emission spectra

38
Q

narrow continuous group of wavelengths

A

band

39
Q

the width of a band at half-height

A

effective bandwitdth

40
Q

what are the two basic ways to select wavelengths?

A

Filters and Monochromators

41
Q

What are the components of a monochromator?

A
  1. Entrance slit
  2. Collimating lens or mirror
  3. prism or grating
  4. focusing element
  5. exit slit
42
Q

what does a collimating lens do to the light?

A

makes it parallel

43
Q

why are monochromators better than prisms?

A

Nearly all commercial monochromators are based on gratings because they are cheaper to make, provide better wavelength separation for the same size element and disperse radiation linearly on the focal plane

44
Q

what are examples of continuum wavelength selectors?

A

fluorite prism - VAC
fused silica or quartz - UV to near IR
glass prism - Visible - Near IR
NaCl - Near IR - far IR
KBr prism - IR - Far IR

45
Q

what are examples of discontinuous wavelength selectors?

A

interference wedge - visible to far IR
interference filter - UV to Far IR
glass filters - visible to near IR

46
Q

____ is the variation in wavelength along the line AB in the focal plane

A

the reciprocal of linear dispersion (nm/mm)

47
Q

_______ is the ability to separate two wavelengths of bandwidth delta lamba

A

resolving power
(smaller distances between gratings increase resolving power)

48
Q

what do most modern monochromators use?

A

echelle grating

Instrumental Analysis (1 decks)

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