exam 2 official woo

Question 1

when is there not an assumed linear relationship in a calibration curve

Answer 1

when we get data points that are outside of our highest and lowest made standards, where can cannot assume linearity

Question 2

what are the assumptions for LLs Analysis

Answer 2

1.) we assume a linear relationship between the response (y-axis) and the concentration (x-axis)

2. all uncertainty is in the y-axis
3. the uncertainty in the y-axis is constant

Question 3

what is the minimum number of points to make a good calibration curve

Answer 3

3 but 4 is the best for a good and accurate linear equation

Question 4

if we have less than 3 points on a calibration curve what happens?

Answer 4

we have lower accuracy and undefined precision

Question 5

what should we do if our concentration is too high to plot on a calibration curve?

Answer 5

we can dilute it

Question 6

what is a calibration check and what does it measure

Answer 6

it is repeated analysis of a calibration standard

this checks precision

Question 7

what is a blank

Answer 7

it is a sample with no analyte that is ran to check for contamination

this affects accuracy and precision

Question 8

what is a lab method spike

Answer 8

it is where we run a sample with a known concentration

if we run one analysis, its a measure of accuracy
if we run multiple analysis, it is a measure of precision

Question 9

what does recovery % tell us?

Answer 9

it allows us to measure the accuracy (or precision if multiple) of our method

we generally want a recovery% close to 100%

Question 10

what is a detection limit?

Answer 10

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

Question 11

what is the assumption with y blank +3*s= mx+b

Answer 11

that y-blank and b are the same

Question 12

do we want low or high limits of detection

Answer 12

low limits of detection

Question 13

what happens to the irradiance (P) as a molecule absorbs light

Answer 13

it decreases

Question 14

what does the absorption tell us

Answer 14

it is directly proportional to the concentration, so the higher the absorption, the higher the concentration

Question 15

what is transmittance

Answer 15

it is the fraction of original light that passes through

Question 16

if we increase the concentration, what happens to the transmittance?

Answer 16

the absorption increases so the transmittance decreases

Question 17

what is the assumption of Ebc

Answer 17

that the slope is equal to Eb

Question 18

are the wavelength and absorption proportional

Answer 18

no, a chemical species may be better or worse at absorbing light at different wavelengths (described by molar absorptivity)

Question 19

when we have too high of a concentration, how is beers law affected and what part of the curve is affected

Answer 19

there is internal screening and the upper end of the curve is affected

Question 20

if we have too low of a concentration, how is beers law affected and what part of the curve is affected

Answer 20

we have a low absorbance and a high transmittance that makes it hard to tell P0 and P from eachothert

Question 21

how do chemical deviations affect beers law

Answer 21

if the chemical environment changes (ex. PH in a titration) the absorption might be different

Question 22

what is true about the phases for liquid chromatography

Answer 22

the mobile phase is liquid and the stationary phase is solid

Question 23

as analytes spend more time in the column, what happens to the curve?

Answer 23

the concentration may become more diluted and result in a wider and lower peak

Question 24

where does separation occur in an HPLC

Answer 24

in the column

Question 25

what is the retention time

Answer 25

the time between the injection and peak

Question 26

what is the retention factor

Answer 26

stationary/mobile time, it gives us a measure of the analytes retention

Question 27

what does it mean if we have a larger retention factor

Answer 27

it means there is more time spent in the stationary phase which may lead to better separation or resolution

Question 28

what does the separation factor describe

Answer 28

it tells us the relative retention of the two solutes and the difference in the partition coefficients

Question 29

if we have a good separation factor, does that mean the separation is good

Answer 29

no, it just describes the differences in the stationary phases

Question 30

what does resolution tell us

Answer 30

it tells us how well things are separated

Question 31

whats the difference between LC and HPLC

Answer 31

in LC, we have lower resolution and larger particles

in HPLC, we have smaller particles in the column that allow for more interactions with the stationary phase, this results in a better resolution but it requires a higher pressure

Question 32

what elutes first in normal phase separation

Answer 32

nonpolar analytes, the mobile phase is nonpolar while the stationary phase is polar

Question 33

what elutes first in reverse phase separation

Answer 33

polar analytes, the mobile phase is polar while the stationary phase is nonpolar

Question 34

what mode of separation do we use to separate nonpolar compounds

Answer 34

reverse phase (np stationary)

Question 35

what mode of separation do we use to separate polar compounds

Answer 35

normal phase (p stationary)

Question 36

when we make the stationary phase and mobile phase more similar, what happens to the retention

Answer 36

the retention times are reduced

Question 37

when we make the stationary phase and mobile phase less similar, what happens to the retention

Answer 37

the retention times are increased

Question 38

what is the mboile phase in gas chromatography

Answer 38

inert gases carry the molecules through a heated column

Question 39

how is gas chromatography related to temperature

Answer 39

when heated, the analyte spends more time in the gaseous mobile phase