Ch 6 Random Errors in Chemical Analysis Flashcards
A bell-shaped curved
Gaussian curve
The difference between the highest and lowest result
Spread
What are the 4 sources of random uncertainties in the calibration of pipet
- Visual judgements
- Variation in the drainage time and angle of the pipet
- temperature fluctuations
- vibrations and drafts
Is the collection of all measurements of interest to the experimenter
Population
A subset of measurement selected from the population
sample
Refers to the quantities such as m and o that define a population or distribution
Parameter
The arithmetic average of a limited sample drawn from a population of data
Sample mean
The true value for the measured quantity
Population mean
A measure of the precision of the population
Population standard deviation
Formula for population standard deviation
o =
Represents the
deviation of a result from the
population mean relative to
the standard deviation.
Quantity z
The square of the
standard deviation
Variance
A normal error curve has several general properties:
(a) The mean occurs at the
central point of maximum frequency,
(b) there is a symmetrical distribution of positive
and negative deviations about the maximum, and
(c) there is an exponential
decrease in frequency as the magnitude of the deviations increases.
Formula for sample standard deviation
s =
The N-1
The number of degrees of freedom
is the standard deviation of a
set of data divided by the square
root of the number of data points
in the set.
Standard error of the mean
Formula of Standard error of the mean
sm = s/ square root of N
If we have several subsets of data, a better estimate of the population standard
deviation can be obtained by ______ the data instead of using only
one data set.
Pooling/ std pool
Equation of SD pool?
S pooled =
is an estimate of the population variance s2
sample variance
is
a curve that shows the symmetrical distribution
of data around the mean of
an infinite set of data
A Gaussian, or normal error curve
is the percent relative standard deviation.
coefficient of variation, CV,
recommends that the symbol
sr be used for relative sample
standard deviation and o’r for
relative population standard
deviation.
International Union of
Pure and Applied Chemistry, IUPAC
is another term that is sometimes used to describe the precision
of a set of replicate results. It is the difference between the largest value in the set and
the smallest.
Spread or range
For a sum or a difference, the standard
deviation of the answer is the square
root of the sum of the squares of the
standard deviations of the numbers
used in the calculation
True
If we have several subsets of data, a better estimate of the population standard
deviation can be obtained by ______ the data instead of using only
one data set. Again
Pooling/ SD pooled
Formula for S pooled
==
is equal to the square
of the standard deviation.
Variance
is
an estimate of the population variance s2
Sample variance
is
the percent relative standard deviation.
coefficient of variation, CV,
Can be obtain by dividing the standard deviation by the mean value
of the data set.
RSD
is another term that is sometimes used to describe the precision
of a set of replicate results. It is the difference between the largest value in the set and
the smallest.
Spread or range
For multiplication or division, the
relative standard deviation of the
answer is the square root of the sum
of the squares of the relative standard
deviations of the numbers that are
multiplied or divided.
True
A much less satisfactory but more common
indicator of the quality of data
Significant figure convention
The __________ in a number
are all of the certain digits plus the first
uncertain digit.
Significant figure
Rules for determining the
number of significant figures:
- Disregard all initial zeros.
- Disregard all final zeros unless
they follow a decimal point. - All remaining digits including
zeros between nonzero digits
are significant.
It is especially important to postpone rounding until the calculation is completed.
True
What do you call that one extra digit beyond the significant digits, which should be carried through all of the computations in order to avoid a rounding error
Guard digit
