Measurment Flashcards
(17 cards)
Measurement
The process of determining the amount, concentration, or physical properties of a substance using standard units and scientific instruments.
Precison
It describes the reproductivity of measurements
Accuracy
Indicates the closeness of a measure to the true or accepted value
Error
The difference between a measured value and the “true” or “known” value
or
The estimated uncertainty in a measurement or experiment
Absolute Error
The absolute error is the difference between the measure value and the true value
-High measurement (+)
-Low measurement (-)
Relative Error
The absolute error divided by the true value
Systematic (Determinate) Error
Cause the mean of a data set to differ from the accepted value
Systematic: Instrumental Errors
Caused by non-ideal instrument behavior, faulty calibrations, or the use of inappropriate conditions
-Usually detectable and correctable
Systematic: Method Error
The non-ideal chemical or physical behavior of the reagents and reactions on which an analysis is based.
-Usually, the most difficult to identify and correct
What causes Instrumental Errors
Examples of Method Error
-Slowness of a reaction
-The incompleteness of a reaction
-The instability of some species
-The occurrence of side reactions
What causes method errors
Carelessness, inattention or personal limitations of the experimenter
Systematic: Personal Error
Errors caused by personal judgment during measurement
Examples of Personal Error
-The color of a solution at the endpoint in a titration
-Level of a liquid in a pipet or burette
Random (Indetermined) Error
Cause data to be scattered more or less symmetrically around a mean value
Gross Error
Occur only occasionally, are often large and may result, and may cause a result to be either high or low
-The product of human errors
-Lead to outliers in a data set
How many errors area actually chemical analysis affected by
At least two
