Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CHEM 211 > unit one > Flashcards

unit one Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

what is the scientific method?

A

an empirical method of acquiring knowledge through tests and experimentation to come up with results

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the 6 steps in the scientific method?

A
  1. formulate question
  2. sampling
  3. sample prep
  4. analysis
  5. interpretation stats and results
  6. draw conclusions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is an analyte?

A

the chemical substance being measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is an assay?

A

the process of determining the amount of analyte in a sample

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is qualitative analysis?

A

concerned with the identification of the elements, ions, compounds present in an unknown sample

what is in the sample?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is quantitative analysis?

A

concerned with the determination of the quantity of one or more components of the sample

how much is in the sample?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is a signal?

A

a measured quantity that is correlated to the amount of analyte

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are the two ways to observe a signal?

A

visual detection and electrical detection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what happens in visual detection of a signal?

A

colour change, formation or disappearance of a solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

when is visual detection used?

A

in volumetric methods of analysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are the advantages of visual detection?

A

simple, low-cost, no maintenance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the disadvantages of visual detection?

A

subjectivity affects accuracy and precision

may not be very sensitive

may require large samples volumes

often time-consuming

low throughput

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is through put?

A

can you get through a lot of samples really quickly?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is electrical detection?

A

measurement of voltage or current

we first measure then we transduce

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is voltage?

A

electrical potential energy (per unit charge)

measured as the electric potential difference between two points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is current?

A

the rate of flow of charge past a point in a circuit (typically electrons moving in a conductor, but not always)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is a transducer?

A

a device that converts an input stimulus (light, heat, pressure) into an electrical output

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the advantages of electrical detection?

A

objective

often more sensitive

often faster

automation

analyze smaller sample volumes

can be portable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the disadvantages of electrical detection?

A

more costly

maintenance and repairs

calibration required

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is noise?

A

unwanted variation in a measured quantity

random fluctuations in the background

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the signal-to-noise ratio?

A

the magnitude of the signal divided by the magnitude of the noise

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how can you increase S/N?

A

multiple scans can be acquired and averaged

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is S/N proportional to?

A

S/N is proportional to the root of the number of measurements (n)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is a sample matrix?

A

all the components of a sample except the analyte

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what is a blank?

A

a man made sample that lacks the analyte, but otherwise contains the solvent, reagents, etc., used in the analysis

tries to approximate the sample matrix

commonly used in analytical experiments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is the limit of detection (LOD)?

A

a method’s detection limit as the smallest concentration or absolute amount of analyte that has a signal significantly larger than the signal from a suitable blank

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what is the formula of the limit of detection?

A

(SA)DL = Smb + 3sigmamb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what is the limit of quantitation (LOQ)?

A

the ability to detect an analyte is not the same as being able to report the concentration with confidence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is the formula for LOQ?

A

(SA)loq = Smb + 10sigmamb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what is a positive control?

A

a standard sample that contains a known quantity of the analyte of interest. helps prevent false negative results

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what is a negative control?

A

a standard sample that does not contain any analyte. helps prevent false positive results

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

what are positive and negative controls used to assess?

A

test validity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

what are figures of merit?

A

analytical parameters used to characterize and validate an analytical method

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

what are the 7 types of figures of merit?

A
  1. LOD and LOQ
  2. accuracy
  3. precision
  4. selectivity
  5. sensitivity
  6. range
  7. robustness
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what is accuracy?

A

the closeness of an experimental value to the true value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

what is precision?

A

agreement among the results

usually it is expressed using the standard deviation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

what is absolute error?

A

the difference between the measured and true value

the value can be + or -

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

what is relative error?

A

the error in a measurement, expressed as a percentage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

what is the formula for absolute error?

A

e = x - u

x = measured

u = true

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

what is the formula for relative error?

A

(x-u)/u * 100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

what are replicates?

A

samples from the same source, run using the same method, under the same conditions, and expected to give the same result in the absence of error

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

what is reproducability?

A

other labs/ scientists reproducing results

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

what is repeatability?

A

repeating your own experiments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

what is selectivity?

A

the extent to which other substances interfere with the determination of an analyte (typically via reactivity/ molecular interactions)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

what is good selectivity?

A

analysis method has minimal interferences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

what is poor selectivity?

A

analysis method prone to certain interferences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

what is interference?

A

a specific chemical substance in a sample matrix that causes a systematic error in a measured quantity

they may act on analyte, reagent, be the source of large background signal, cause negative or positive bias, or cause absolute or proportional errors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

what is a masking agent?

A

a reagent that prevents one or more components in a sample matrix from interfering with an analysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

what is specificity?

A

a method that is 100% selective

extremely rare

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

what is the formula for selectivity?

A

S sample = S analyte + S Interference = KaCa + KiCi

Ka,i = Ki/Ka

> 1 = more selective for interference

< 1 = more selective for analyte

51
Q

what is sensitivity?

A

the ability of a method to measure small changes in concentration of an analyte

52
Q

what is sensitivity determined by?

A

the slope of the calibration curve

53
Q

what is range?

A

concentration range over which we have acceptable linearity, accuracy and precision

54
Q

what is linear range?

A

analyte concentration over which the response is proportional to concentration

55
Q

what is dynamic range?

A

the range an instrument can read (there is a measurable response, but it may not be linear)

56
Q

what is robustness?

A

ability of a method to withstand small, uncontrolled changes in the operation parameters

ex. ph, temp

57
Q

what does robustness tell us?

A

how reliable the method is

58
Q

what is the formula for sensitivity?

A

delta Sa = Ka * delta Ca

delta Ca and Ka have an inverse relationship

Ka affects the slope

59
Q

what does it mean in terms of sensitivity if there is a higher slope?

A

more sensitive

60
Q

what does linear & dynamic range look like on a graph?

A

look at graph

61
Q

what are the two types of error?

A

random/ indeterminate

systematic/ determinate

62
Q

what is random error?

A

introduce uncertainty

symmetric about the true value

treat with statistics

can’t change

63
Q

what is systematic error?

A

introduce bias

the measured value will always be higher or lower than its true value

can change

can be proportional or constant

64
Q

what are the types of systematic errors?

A

instrument errors

method errors

personal errors

65
Q

what are instrument errors (SE)?

A

minimize with careful, regular calibration

voltage drift

can usually be corrected

66
Q

what are method errors (SE)?

A

Chem does not behave as expected

most difficult to identify and correct

incomplete rxn

interference from non-analytes

false positive/ negative results

67
Q

what are personal errors (SE)?

A

Incorrect recording of data

deviations from an established method

68
Q

what is a proportional error (SE)?

A

Always measuring a voltage 10% higher than the true value

its effect is independent of the magnitude of the measurement

69
Q

what is a constant error (SE)?

A

Always measuring a voltage 1 mV lower than the true value

the constant error is small if measuring a 2V signal (0.1%) but large if measuring 20 mV signal (10%)

70
Q

what can the line of best fit be determined by?

A

minimize the sum of squares of the residuals

called sum of least squares

71
Q

what is the sum of least squares?

A

minimizes the residuals between the data points and the line of best fit

assumes there is only error in the y data

72
Q

what is the formula for sum of least squares?

A

di = yi - (mx + b)

73
Q

how can you tell selectivity through a calibration curve?

A

the selectivity of a method for compound one versus two is reflected by the ratio of their slopes m1/m2

74
Q

what is sampling?

A

the process by which a sample population is reduced to a size suitable for lab analysis

the composition of the sample must be representative of the population

75
Q

what is the sampling process?

A
  1. identify the population
  2. develop a sampling strategy
  3. collect and preserve a gross sample(s)
  4. reduce the gross sample(s) to a lab sample
  5. replicate analyses of the sample(s)
76
Q

how do we define the problem for sampling?

A

expected conc range of analyte?

accuracy and precision required?

where, when, how many samples to take, and what size?

77
Q

why and how must you store samples?

A

protect from light, control temp and pH

store most samples in glass but store metal solutions in plastic

78
Q

what does homogenization mean for sampling?

A

may require crushing & grinding, drying, digesting, decomposing

79
Q

what the overwhelming matrix effects?

A

requires extraction, precipitation, distillation, or other separations of analyte from interferences

80
Q

what happens if the analyte is too dilute for reliable analysis?

A

requires pre-conc steps such as extraction or evaporation

81
Q

what is a calibration curve?

A

a graph of the response of an instrument vs. the concentration of standard solutions

82
Q

what are standard solutions?

A

created using known and increasing amounts of the analyte

83
Q

what instrument is used for calibration curves?

A

spectrophotometre

responds to concentration changes using a signal

84
Q

what does a spectrophotometre measure?

A

absorbance

85
Q

what is absorbance?

A

the amount of light that is absorbed by a solution

86
Q

what is absorbance proportional to?

A

to the concentration

87
Q

what is beer’s law?

A

A = (molar absorptivity coefficient) b C

88
Q

how do we find the unknown?

A

use linear regression

take the equation of the line, equate y to the measured absorbance

solve for x

plug this x in for Cf in the formula (CiVi = CfVf)

89
Q

what is the matrix effect?

A

the combined effect of all non-analyte components in a sample on the quantitative measurement of the analyte

this terminology is used when a specific interference is not known

90
Q

describe standard addition

A

add known quantities of analyte to the unknown solution

extrapolate unknown from the calibration curve

means of accounting for matrix effects

91
Q

what are the advantages of standard addition?

A

accounts for matrix effect

92
Q

what are the disadvantages of standard addition?

A

requires lots of the sample

93
Q

describe external standards

A

create standard solutions with varying and known concentration of the analyte

interpolate unknown from the calibration curve (find x intercept from the y -intercept)

94
Q

what are the advantages of external standards?

A

simple, easy, and cost effective

95
Q

what are the disadvantages of external standards?

A

cannot account for inconsistencies in instrument or matrix

96
Q

what is internal standards?

A

an intentionally added substance of known quantity that is not expected to be found in the sample (different than the analyte) but is expected to behave similarly

the internal standard is analyzed with the analyte to account for losses during sample processing or fluctuations in instrument signals

use this when it is not possible to treat samples and standards the same

97
Q

what is single point calibration?

A

using 1 standard to determine the relationship between signal and concentration

98
Q

what are the advantages of multi-point calibration?

A

systematic error in one standard is minimized by the existence of other standards

calibration curve allows determination of relation between signal and concentration

99
Q

what are the advantages of internal standards?

A

accounts for losses throughout analysis

100
Q

what are the disadvantages of internal standards?

A

costly

extra-step

101
Q

what is a probability distribution?

A

a function that describes the probability of occurrence of a variable

102
Q

what is normal distribution?

A

the normal distribution is one type of distribution which is symmetric about the mean

bell curve

AKA gaussian distribution

the mean, median, and mode are equal

the total area under the curve is 1

width and height determined by the standard deviation

103
Q

how much area is covered with 1 std dev?

A

68.3%

104
Q

how much area is covered with 2 std dev?

A

95.4%

105
Q

how much area is covered with 3 std dev?

A

99.7%

106
Q

what is degree of freedom?

A

the number of independent measurements

107
Q

what are details about a population called?

A

parameters

108
Q

what are details about a sample called?

A

statistics

109
Q

what is mean?

A

average value

110
Q

what is standard deviation?

A

spread of all values measured (degree of spread)

111
Q

what are the 4 tests used?

A

1) case 1 t-test
2) case 2 t-test (w or wo f-test)
3) case 3 t-test
4) Grubbs test

112
Q

what is the null hypothesis?

A

often used to test experimental results

postulates that two observed quantities are the same

assume two results are the same, then apply a test to see if the null hypothesis can be statistically rejected

113
Q

what is the difference between a null hypothesis and an alternative hypothesis?

A

null = claims there is no effect

alternative = has an effect

114
Q

what are the two things we can do with a null hypothesis?

A

reject the null hypothesis (accept alternative)

fail to reject the null hypothesis (accept the null)

115
Q

what is a confidence level?

A

a probability that we will reject the null hypothesis when it is infact true

116
Q

what is a confidence interval?

A

defines a range of values, centred on the sample mean, that have a certain probability of including the true population mean

117
Q

what are the limits of a confidence interval called?

A

confidence limits

118
Q

what is the confidence level?

A

the likelihood that the true value falls within this range

aka the probability

119
Q

what is the t-test?

A

the t statistic permits use of sample data to test hypotheses about unknown population means without knowledge of the population standard deviation

accounts for limited sample size so as to better reflect the population values

120
Q

what is the case 1 t-test?

A

obtain a sample containing a known amount of analyte and then comparing the measured value on this sample to the actual value

if LHS < RHS, no diff

if LHS > RHS, diff

t exp > t crit, diff

t exp < t crit, no diff

121
Q

what is the case 2 t-test?

A

compare two means to see if they’re statistically different

results of two diff analyses of the same sample

samples are not connected

stdev must be pooled

LHS < RHS, no diff

LHS > RHS, diff

t exp > t crit, diff

t exp < t crit, no diff

122
Q

what is the F-test?

A

in order to compare two methods, it is imp to know whether the variabilities for both methods are the same.

we use the variance formula

f exp < f crit, no diff

perform f test, if no diff perform case 2, if diff there do the DOF formula

123
Q

what is a case 3 t-test?

A

aka paired t-test

uses paired/ matched measurement data

samples are connected

t calc < t crit, no diff

124
Q

what is the G test?

A

statistical test used to exclude outliers from a data set

G exp > G crit = outlier

CHEM 211 (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions