Unit
Analysis
In science, it is not uncommon to change from one system of
measurement to another. The best method to accomplish this
change is unit analysis.
In science calculations, the units are very important and
must be treated in the same way as constants and variables are
treated in algebra.
Notice in the example how the units multiply, divide and
cross cancel just like numbers and variables.
Conversions
Science calculations require close examination of the
units. Therefore, you must know the conversion factors that
allow you to make the desired calculations.
Common Conversion Factors
This Per That Problems
The typical type of chemistry problem is a "this per
that" or what is called a conversion problem. An
example of a this per that would be 12
inches per 1 foot.
The hardest part of a this per
that is knowing the conversion factor (this per that).
Once you know the conversion factor all you have to do is set
up the equation, verify your units, and plug&chug (put it
in the calculator).
Example
There are 500 monkeys and you can put 5
monkeys in a cage.
How many cages will you need?
500
monkeys 5 monkeys
per cage How many
cage?
Reasoning tells me that if I divide 500 by
5 I will need 100 cages.
The above example is a this per
that problem and similar in logic to the types of
problems you will do in chemistry. So, let's look at it set up
like a chemistry problem.
Note that monkeys cancel out and cages is
our new unit.
