Exam 1 Flashcards
weighing by mass used for…
hygroscopic reagents
TC
to contain
TD
to deliver
sample
a representative portion of the material of interest
matrix
everything in the sample
analyte
component of interest in the sample
trace amount
ppb or <0.01%
minor component amount
ppt or 0.01-1%
major component amount
pph or >1%
defining replicates
dividing into aliquots
classical wet methods
gravimetric
titration
instrumental methods
separation techniques
spectroscopy
electrochemical
classical methods based on…
requires…
mass & volume, chemical properties
well-defined rxn stoichiometry
instrumental methods based on…
signals generated by the analyte with an instrument
relationship between signal and concentration in instrumental methods
s = kC
k is a constant
screening assay
determines what exists in a sample
information provided by analytical chemistry
qualitative
quantitative
chemical identification
structural analysis
property characterization
spatial analysis
time-dependent analysis
formal concentration (F)
molarity of a strong electrolyte
molality
moles of solute / kg of solvent
advantage of molality vs molarity
molality does not depent on temperature
ppm =
(mass substance / mass sample)10^6
mg/L (density @1 g/mL)
mg/kg
μg/g
ng/mg
ppb =
(mass substance / mass sample)10^9
μg/L (density @ 1 g/mL)
μg/kg
if K > 1….
forward rxn is favored
define significant figures
total number of digits required to write a number in scientific notation without a loss in accuracy
sig fig rules for addition and subtraction
retain same number of decimal places of the number with the fewest
sig fig rules for multiplication and division
number with the greatest uncertainty determines sig figs of the product/quotient
sig fig rules for logarithm-generated numbers
only mantissa is significant, and includes 0 directly after decimal point
the number of sig figs in the number you are taking the log of determines the sig figs in the mantissa
analytical concentration
does not consider what happens to solute after dissolution
species concentration
considers chemical changes to solutes
specific gravity
Dsoln / 1 g/mL = SG (no units)
ratio of denisty of soln to density of H2O @ 4° C
purity grades in order from least to greatest purity
technical/lab grade
certified ACS & USP, BP, EP, NF, FCC grade
biotech grade
HPLC grade
trace metal grade
advantage of using stock soln
allows use of larger solute masses - less relative uncertainty
define p function
pX = -log(X)
2 types of error
systematic (determinate)
random (indeterminate)
detection of systematic error
multiple checks with multiple analysts
test a known/blank standard
unusual trends
use of different analytical methods
accuracy
difference between experimental value and true value
precision
variation in experimental results
absolute error (e) =
e = x - μ
x = experimental result
μ = true value
relative error (eR) =
eR = e/μ
e = absolute error
μ = true value
standard deviation describes…
precision
variance =
s^2
relative standard deviation (ppt) =
RSD = s/x(1000)
good, mediocre, bad RSD for classical wet methods
good: <4
mediocre: 4-10
bad: >10
good RSD for instrumental methods
<10
__% of measurements lie within +/-1 s of x
68
___% of measurements lie within +/-2 s of x
95
why does increasing n make x more accurate?
the more values there are, the more likely it is that (+) and (-) random errors cancel one another out
relative error =
sy / y
CI =
x ± (ts) / √n
CI represents…
range around the mean, for a certain confidence level, within which the true value actually lies
criteria for suspicion of data points
lies >±2 s of x
lies outside CI
seems suspicious based on experience
2 tests for outliers
Dixon (Q)
Grubbs (Tn)
Q =
|xo - xn| / xhigh - xlow
xn = nearest value to outlier
Tn =
|xo - x| / s
steps to make a solution
- transfer measured solute to flask
- dissolve in less than desired volume solvent and mix
- add more solvent, less than desired volume, and mix
- dilute to volume mark
- cap, mix and invert many times
null hypothesis
that there is no difference between your result and the reference value
purpose of student’s t test
tests accuracy of method with a known standard
t = |x - μ| / (s / √n)
μ = reference value
student’s t test
purpose of F test
comparison of precisions between 2 data sets
purpose of s pool test
comparing the means of two data sets with similar precisions (via the F test)
purpose of tcalc test
comparing the means of two data sets with dissimilar precisions (via the F test)
coefficient correlation (r) describes…
how well the data points fit a linear regression
if r = 1…
if r is high…
if r is low…
r = 1; line fit is perfect
high r; more confidence
low r; more scattering of data points
used to determine if a data set is linear
residual plot
in a residual plot, true linear plots have data…
scattered around 0
purpose of calibration curve
use linear equation of a best-fit line to extrapolate x from y of an experimental value (or vice versa)
