Measurement Errors, Sig Figs and Dimensional Analysis Flashcards
Arise from experimental variables that cannot be controlled or determined and affect precision.
Random or indeterminate errors
Occur when instruments or measuring devices are uncalibrated or are calibrated improperly. They have the same effect on all samples. Affects accuracy of results.
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
Independent of the size of the sample being analyzed.
Constant Errors
Decrease or increase in proportion to the size of the sample.
Proportional Errors
Solution contains the solvent and all the reagents in an analysis.
Blank solution
Solution contains the sample, solvent and all the reagents in an analysis.
Analyte
Refers to the collection of all the constituents in the sample.
Matrix
The mean value of a dataset is also called
Average
A sample of about the same size that is carried through an analysis in exactly the same way.
Replicate
The middle value in a set of data that has been arranged in numerical order.
Median
The closeness of results to others obtained in exactly the same way.
Precision
The closeness of a measured value to the true or accepted value and is expressed by the error.
Accuracy
The difference between the measured value and the true value.
Absolute Error
The absolute error divided by the true value.
Relative Error
Occur infrequently and often result from an experimental blunder such as misreading a scale or interpreting a number incorrectly.
Gross Error
An occasional result in replicate measurements that differs significantly from the other results.
Outlier
Measures the systematic error associated with an analysis.
Bias
Systematic errors lead to bias.
Bias caused by rounding
Number Bias
Can be caused by prejudice or bias.
Personal Bias
Aids in the detection of systematic instrument errors.
Calibration
Substances sold by the National Institute of Standards and Technology (NIST) and certified to contain specified concentrations of one or more analytes.
Standard Reference Material (SRM)
As the size of a measurement increases, the effect of a constant
error decreases.
The number of digits in a value, often a measurement, that contribute to the degree of accuracy of the value.
Significant Figures
Rules for Significant Figures
All non-zero digits are significant. For example, 198745 contains six
significant digits.
All zeros that occur between any two non-zero digits are significant. For example, 108.0097 contains seven significant digits.
All zeros that are on the right of a decimal point and to the left of a nonzero digit is never significant. For example, 0.00798 contained three significant digits.
If the number is greater than 1, all zeros that are on the right of a decimal point are significant, only if, a non-zero digit does not follow them. For example, 20.00 contains four significant digits.
If the number is less than 1, All the zeros that are on the right of the last non-zero digit, after the decimal point, are significant. For example, 0.0079800 contains five significant digits.
For numbers that do not contain decimal points, the trailing zeros (zeros after the last non-zero digits) are may or may not be significant. For example, 400 cm may contain 1 significant figure (4), 2 significant figures (40) or 3 significant figures (400). However, we can reduce this ambiguity on the numbers by using scientific notation. Thus, 4 𝑥 102 will have 1 significant figures, 4.0 𝑥 102 will have 2 significant figures and 4.00 𝑥 102 will have 3 significant figures.
- Addition and Subtraction rules for significant figures
➢The answer must not contain more digits to the right of the decimal point than the fewest of any of the figures being add or subtract. - Example: 89.332 + 1.1 = 90.432 = 90.4
- Multiplication and Division rules for significant figures
➢The product or quotient is determined by the original number that
has the smallest number of significant figure. - Example: 2.8 × 4.5039 = 12.61092 = 13
Used to convert from one unit of measurement to another unit.
Factor-label Method / Dimensional Analysis / Unit Conversions
