Chem1 General Chemistry Virtual Textbook

The Measure of Matter
all about units, measurements, and error

> The instruments provide the numbers,
> but the user must judge their meaning

1 Units and dimensions

Scales and units • the SI base units • SI decimal prefixes
units outside the SI • derived units • dimensional analysis
unit conversions • units and their ranges in Chemistry

2 The meaning of measure

Uncertainty is certain! • random and systematic error
absolute and relative uncertainty • dealing with scatter: the mean
accuracy and precision

3 Significant figures and rounding off

Digits: significant and otherwise • implied uncertainty of a number
rules for rounding off • rounding results of calculations
roundoff error

4 Reliability of a measurement

Attributes of a measurement • more than one answer:
dispersion of the mean • systematic error
can you trust the results? • the standard deviation

5 Drawing conclusions from data

The bell-shaped curve • confidence intervals and levels
using statistical tests to make decisions
how to lie with statistics: some dangerous pitfalls