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Chem 31 > exam 2 > Flashcards

exam 2 Flashcards

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1
Q

What is wavelength

A

it is the linear distance between successive maxima or minima

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2
Q

what is frequency

A

it is the number of oscillations of the field that occur per second

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3
Q

what is the product of frequency and wavelength

A

the speed of light

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4
Q

What happens to the energy of a molecule when light is absorbed

A

it increases

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5
Q

What is the irradiance

A

it is P it is the energy per second per unit area of the light beam

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6
Q

what happens to the irradiance when light is absorbed by the analyte

A

P decreases

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7
Q

What is P0 and it’s relationship to P

A

P0 is the irradiance before it passes through the sample, it is greater than P which is the irradiance after it passes through the sample

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8
Q

What is transmittance

A

it is T (P/P0) it is the quantity of light that passes through the sample

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9
Q

what is absorbance and how is it connected to concentration?

A

the absorbance is how much of the light is absorbed, it can be used to tell us how much concentration is there

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10
Q

In a spectroscopic experiment with beers law, what is the y-axis and what is the x-axis? What is the slope?

A

the y-axis is the absorption, it is dependent on the concentration

the x-axis is the concentration, it is independent

the slope is the molar absorptivity x the wavelength

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11
Q

what is b in beers law

A

the pathlength

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12
Q

what is QA and QC

A

it is a sample that we can analyze to represent the precision and accuracy of our method

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13
Q

what are calibration checks

A

they are repeated analyses of a calibration standard that checks the precision

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14
Q

what are blanks

A

they are samples containing no analyte, they check for contamination which could affect accuracy and precision

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15
Q

what are lab, method spikes

A

they are samples with a known amount of analyte and analyzed as a sample

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16
Q

when are lab method spikes analyzing accuracy

A

when it is a single analysis

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17
Q

when are lab method spikes analyzing precision

A

when it has multiple analyses

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18
Q

what is a detection limit

A

it is the lowest amount of analyte in a sample that gives a signal that we can say is significantly different from the blank signal

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19
Q

what is the signal detection limit

A

=y blank + 3s

where y blank is the signal in blank and s is the standard deviation in the replicates

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20
Q

what is the relationship between y blank + 3s = mx+b

A

y blank is equal to b (the y-intercept)

the concentration detection limit is x= (3s)/m

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21
Q

what is the purpose of signal detection limits

A

they allow us to differentiate between error, lab contamination, and the presence of analyte in a sample

22
Q

does the best method have a high or low limit of detection?

A

the method is better with a low LOD

23
Q

if the detection is less than the limit how do we describe it?

A

it is not zero. we say it is between 0- and the line of detection(ex. 0.1 ug/L)

24
Q

is absorption constant with respect to the wavelength

A

no, it varies. We need to make our standards the same wavelength

25
Q

what is molar absorbtivity

A

he molar absorptivity is a measure of how well the species absorbs the particular wavelength of radiation that is being shined on it.

26
Q

what type of transition gives a high molar absorbtivity

A

ones that are more efficient

27
Q

if you have a higher molar absorbtivity, what is true of the absorbance

A

it is higher, the absorptivity is directly proportional to the absorbance

28
Q

what is the absorbance directly proportional to

A

tha absorbance is propportional to the concentration of the absorbing material, the constant pathlength, and the molar absorptivity

29
Q

does wavelength factor in absorbance

A

yes but in a different way, the absorbance is a constant that various depending on the wavelength of the light

30
Q

is absorption directly proportional to the wavelength

A

no, the absorbance is not directly proportional to the wavelength.

Each substance absorbs light at different wavelengths

31
Q

whats the difference between molecular and atomic spectroscopy

A

in molecular spec, we can see various bond vibrations and molecular transitions

in an atomic spec, we only see the single transition from the ground state so there is only one absorption frequency

32
Q

what is internal screening

A

when the concentration is too high and a shadow effect occurs that causes the calibration curve to flatten out

33
Q

what happens if our concentrations are too low

A

the P0 and P are basically the same and we can’t see a significant difference between the two

34
Q

what is a chemical deviation in beers law

A

when an analyte changes in the presence of the solvent to form compounds that have a different light absorptivity than the parent species, this can be controlled with a buffer which resists a PH change

35
Q

what is an instrumental deviation

A

occurs from the instrument being ass

36
Q

if there are two absorbing species in a mxture

A

the absorbance at a given wavelength will be the result of the absorbance of both species

37
Q

why do we want a low detection limit

A

it gives us more room to capture our concentration

38
Q

what is the purpose of recovery% it tells us how accurate a method is

A
39
Q

what is chromatography

A

it allows us to separate, identify, and purify the components of a mixture for qualitative and quantitative analysis

40
Q

what is an LLE

A

it is a liquid liquid extraction which is a classical form of separation

it allows us to transfer the analyte of interest from one phase into another

41
Q

what are the two phases of an LLE

A

the aqueous phase (S1) and the Organic phase (S1)

42
Q

what is the organic phase usually?

A

the second phase, it is usually on top since it is less dense

43
Q

does the K change with the concentration of S

A

no, it is constant at equilibrium

44
Q

When talking about LLE’s, what does it mean when K>1

A

it means we have more organic concentration in phase 2

45
Q

when talking about LLEs, what does it mean when K<1

A

it means we have less organic concentration in phase 2

46
Q

What type of material would we see in the organic layer of an LLE?

A

molecules with a lack of polar character, not charged

47
Q

what type of material would we see in the aqueous layer of an LLE

A

molecules that have polar character and are charged

48
Q

what is the mobile phase

A

the phase of an LLE that is moving; solvent is moving through a column

49
Q

what is the stationary phase

A

the phase of an LLE that is solid; solvent is fixed in a column

50
Q

molecules that like the mobile phase move through the system in what fashion?

A

they move through it quickly

51
Q

molecules that like the stationary phase move through the system in what fashion?

A

they move through it slowly

Chem 31 (14 decks)

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