In chemistry, it is not uncommon to change from one system of measurement to another. The best method to
accomplish this change is unit analysis.
In chemistry 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.
Chemistry 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).
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.