Measurement Errors, Sig Figs and Dimensional Analysis

Question 1

Arise from experimental variables that cannot be controlled or determined and affect precision.

Answer 1

Random or indeterminate errors

Question 2

Occur when instruments or measuring devices are uncalibrated or are calibrated improperly. They have the same effect on all samples. Affects accuracy of results.

Answer 2

Systematic or determinate errors

Question 3

Caused by nonideal instrument behavior, by faulty calibrations, or by use under inappropriate conditions.

Answer 3

Instrumental Errors

Question 4

Arise from nonideal chemical or physical behavior of analytical systems.

Answer 4

Method Errors

Question 5

Result from carelessness, inattention, or personal limitations of the experimenter.

Answer 5

Personal Errors

Question 6

Independent of the size of the sample being analyzed.

Answer 6

Constant Errors

Question 7

Decrease or increase in proportion to the size of the sample.

Answer 7

Proportional Errors

Question 8

Solution contains the solvent and all the reagents in an analysis.

Answer 8

Blank solution

Question 9

Solution contains the sample, solvent and all the reagents in an analysis.

Answer 9

Analyte

Question 10

Refers to the collection of all the constituents in the sample.

Answer 10

Matrix

Question 11

The mean value of a dataset is also called

Answer 11

Average

Question 12

A sample of about the same size that is carried through an analysis in exactly the same way.

Answer 12

Replicate

Question 13

The middle value in a set of data that has been arranged in numerical order.

Answer 13

Median

Question 14

The closeness of results to others obtained in exactly the same way.

Answer 14

Precision

Question 15

The closeness of a measured value to the true or accepted value and is expressed by the error.

Answer 15

Accuracy

Question 16

The difference between the measured value and the true value.

Answer 16

Absolute Error

Question 17

The absolute error divided by the true value.

Answer 17

Relative Error

Question 18

Occur infrequently and often result from an experimental blunder such as misreading a scale or interpreting a number incorrectly.

Answer 18

Gross Error

Question 19

An occasional result in replicate measurements that differs significantly from the other results.

Answer 19

Outlier

Question 20

Measures the systematic error associated with an analysis.

Answer 20

Bias

Question 21

Systematic errors lead to bias.

Question 22

Bias caused by rounding

Answer 22

Number Bias

Question 23

Can be caused by prejudice or bias.

Answer 23

Personal Bias

Question 24

Aids in the detection of systematic instrument errors.

Answer 24

Calibration

Question 25

Substances sold by the National Institute of Standards and Technology (NIST) and certified to contain specified concentrations of one or more analytes.

Answer 25

Standard Reference Material (SRM)

Question 26

As the size of a measurement increases, the effect of a constant
error decreases.

Question 27

The number of digits in a value, often a measurement, that contribute to the degree of accuracy of the value.

Answer 27

Significant Figures

Question 28

Rules for Significant Figures

Answer 28

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

Question 29

Used to convert from one unit of measurement to another unit.

Answer 29

Factor-label Method / Dimensional Analysis / Unit Conversions