exam 2

Question 1

What is wavelength

Answer 1

it is the linear distance between successive maxima or minima

Question 2

what is frequency

Answer 2

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

Question 3

what is the product of frequency and wavelength

Answer 3

the speed of light

Question 4

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

Answer 4

it increases

Question 5

What is the irradiance

Answer 5

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

Question 6

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

Answer 6

P decreases

Question 7

What is P0 and it’s relationship to P

Answer 7

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

Question 8

What is transmittance

Answer 8

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

Question 9

what is absorbance and how is it connected to concentration?

Answer 9

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

Question 10

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

Answer 10

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

Question 11

what is b in beers law

Answer 11

the pathlength

Question 12

what is QA and QC

Answer 12

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

Question 13

what are calibration checks

Answer 13

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

Question 14

what are blanks

Answer 14

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

Question 15

what are lab, method spikes

Answer 15

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

Question 16

when are lab method spikes analyzing accuracy

Answer 16

when it is a single analysis

Question 17

when are lab method spikes analyzing precision

Answer 17

when it has multiple analyses

Question 18

what is a detection limit

Answer 18

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

Question 19

what is the signal detection limit

Answer 19

=y blank + 3s

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

Question 20

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

Answer 20

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

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

Question 21

what is the purpose of signal detection limits

Answer 21

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

Question 22

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

Answer 22

the method is better with a low LOD

Question 23

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

Answer 23

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

Question 24

is absorption constant with respect to the wavelength

Answer 24

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

Question 25

what is molar absorbtivity

Answer 25

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

Question 26

what type of transition gives a high molar absorbtivity

Answer 26

ones that are more efficient

Question 27

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

Answer 27

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

Question 28

what is the absorbance directly proportional to

Answer 28

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

Question 29

does wavelength factor in absorbance

Answer 29

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

Question 30

is absorption directly proportional to the wavelength

Answer 30

no, the absorbance is not directly proportional to the wavelength. Each substance absorbs light at different wavelengths

Question 31

whats the difference between molecular and atomic spectroscopy

Answer 31

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

Question 32

what is internal screening

Answer 32

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

Question 33

what happens if our concentrations are too low

Answer 33

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

Question 34

what is a chemical deviation in beers law

Answer 34

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

Question 35

what is an instrumental deviation

Answer 35

occurs from the instrument being ass

Question 36

if there are two absorbing species in a mxture

Answer 36

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

Question 37

why do we want a low detection limit

Answer 37

it gives us more room to capture our concentration

Question 38

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

Question 39

what is chromatography

Answer 39

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

Question 40

what is an LLE

Answer 40

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

Question 41

what are the two phases of an LLE

Answer 41

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

Question 42

what is the organic phase usually?

Answer 42

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

Question 43

does the K change with the concentration of S

Answer 43

no, it is constant at equilibrium

Question 44

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

Answer 44

it means we have more organic concentration in phase 2

Question 45

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

Answer 45

it means we have less organic concentration in phase 2

Question 46

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

Answer 46

molecules with a lack of polar character, not charged

Question 47

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

Answer 47

molecules that have polar character and are charged

Question 48

what is the mobile phase

Answer 48

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

Question 49

what is the stationary phase

Answer 49

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

Question 50

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

Answer 50

they move through it quickly

Question 51

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

Answer 51

they move through it slowly