Quant Lec.5: Experimental Error

Chapter 3

Absolute Uncertainty

An expression of the margin of uncertainty associated with a measurement. Also could refer to the difference between a measured value and the '“true” value.

Accuracy

A measure of how close a measured value is to the “true” value.

Antilogarithm

antilog of a is b : 10^a = b

Atomic Mass

Number of grams of an element containing Avogadro’s

number of atoms. For elements with multiple stable isotopes, the atomic

mass is a weighted average refl ecting the abundance of the different iso-

topes.

Certified Reference Material

Samples sold by national measurement

institutes and containing known quantities of analytes to test accuracy of

analytical procedures.

Characteristic

The part of a logarithm at the left of the decimal point.

Determinate (Systematic) Error

Flaw in equipment or design of an experiment

Indeterminate (Random) Error

Uncontrolled or uncontrollable variables in the measurement

Logarithm

log n = a

ln(x) = a

Mantissa

The part of a logarithm to the right of the decimal point.

Natural Logarithm

ln(a) = b; if e^b = a

Precision

How well replicate measurements agree with one another.

Random Error

A type of error, which can be either positive or negative

and cannot be eliminated, based on the ultimate limitations on a physical

measurement. Also called indeterminate error.

Relative Uncertainty

Uncertainty of a quantity divided by the value of the

quantity. It is usually expressed as a percentage of the measured quantity.

Significant Figure

The number of signifi cant digits in a quantity is the

minimum number of digits needed to express the quantity in scientifi c

notation without loss of precision. In experimental data, the fi rst uncertain

fi gure is the last signifi cant fi gure.

Systematic Error

Error due to procedural or instrumental factors that cause

a measurement to be consistently too large or too small. The error can, in

principle, be discovered and corrected. Also called determinate error.