Chapter 10: Summary Flashcards
all measurements contain __ and __
- errors
- uncertainties
what is always provided
- estimate of quality
- reliability of collected data
what is prepared to improve the reliability of results
two to five replicate samples
what is used as a measure of central value of data
- mean or
- median
what is measured to demonstrate reproducibility of data
precision
why is it often more difficult to determine the accuracy of results than the precision
because true value is seldom known
precise measurements are not __ all of the time
accurate
arise from experimental variables that cannot be controlled or determined
Random or indeterminate errors
Random error affect __
precision
occur when instruments or measuring devices are uncalibrated or are calibrated improperly
Systematic or determinate errors
caused by nonideal instrument behavior, by faulty calibrations, or by use under inappropriate conditions
instrumental errors
arise from nonideal chemical or physical behavior of analytical systems
method errors
result from carelessness, inattention, or personal limitations of the experimenter
personal errors
are independent of the size of the sample being analyzed
constant errors
decrease or increase in proportion to the size of the sample
proportional errors
most personal errors can be minimized by what
- careful, disciplined laboratory work
- careful choice of methods and instruments
what is best way to estimate the bias of an anlytical method
analyzing standard reference materials (SRMs)
contains the solvent and all the reagents in an analysis
blank
blank that contain added constituents to simulate the __ __
sample matrix
refers to the collection of all the constituents in the sample
matrix
Random, or indeterminate, errors affect measuremetn __
precision
where do random errors arise from
experimental variables that cannot be controlled or determined
Example of random errors
- random fluctuations in electrical noise
- random inconsistencies in measurement readings
- random changes in laboratory temperature
systematic, or determinate, errors affect the __ of results
accuracy
systematic errors often occur when?
instruments or measuring devices are uncalibrated or calibrated improperly
systematic errors can be very __ and __ to detect
- subtle
- difficult
substance being determined
analyte
occur infrequently and often result from an experimental blunder such as misreading a scale or interpreting a number incorrectly
gross errors
occasional result in replicate measurements that differs significantly from the other results
outlier
- measures the systematic error associated with an analysis
- has negative sign if it causes the results to be low and positive sign otherwise
bias
sign of bias if it causes results to be low
negative sign
sign of bias if it causes results to be high
positive sign
- determines the relationship between a measured quantity and the analyte concentration
- very important part of any analytical procedure
calibration
Of the three types of systematic errors encountered in a chemical analysis, what is usually the most difficult to identify and correct
method errors
independent of the size of the sample being analyzed
constant errors
decrease or increase in proportion to the size of the sample
proportional errors
Equation for Mean
x̄ = sum of all measurements / no. of measurements
Equation for Absolute Error
E = xi - xt
Equation for Deviation from the mean
di = |xi - x̄ |
Equation for Relative Error
Er = (xi - xt/ xt) x 100%
