Uncertainty in measurements Flashcards
Precision
the closeness of a set of results/data that have been obtained in exactly the same way
Accuracy
the closeness of data to the true value
Absolute error
the magnitude of difference between the true value and measured value
Relative error
absolute error divide by the true value
Absolute error formula
E = Xm - Xt
relative error formula
E = (Xm - Xt)/ Xt
Percentage error formula
E = (Xm - Xt)/Xt x 100
Random error
existing fluctuations of any measuring apparatus
Systematic error
a consistent difference between a measurement and its true value
Standard deviation
a measure of precision of a small sample of data
When the values are tightly bunched together and the bell shape curve is steep the SD is _____ and the uncertainty of measurement is _____
small/low
small
Examples of instrument errors and how they can be eliminated
caused by faulty calibrations, instruments being used under different conditions from which they were calibrated or unstable power supply. These errors can be eliminated by calibration or checking the instrument against a standard.
example of personal errors and how can it be eliminated
result from personal judgement ie. colour of a solution at the end point in a titration or estimating measurements between 2 scale markings. These errors can be minimised by care and self discipline
apparatus used to measure mass
top loading balance, analytical balance
Examples of method errors
behaviour of reagents and reactions such as incompletedness of reaction or occurrence of side reactions which interfere with the measuring process.
