Units and Dimensions
Almost all measurable physical quantities have units.
Errors in units are the most common student mistakes.
In practice they can also be disastrous (even fatal).
This topic introduces a reliable method for dealing with and changing units.

A quantity should be thought of as a product of 2 parts: a pure number x a unit
For example the mass of a man is 63 kg, i.e. 63 x 1 kg.

When doing calculations the units are as much a part of the calculation as the numbers. Never just calculate with numbers and hope that the units will work out. Often they will, but when they don't the results can be disastrous.

Many different unit systems are available and chemists often use non-standard units for convenience.