Math Skills Review
Dimensional Analysis (also called Factor-Label Method or the Unit Factor Method) is a problem-solving method that uses the fact that any number or expression can be multiplied by one without changing its value. It is a useful technique. The only danger is that you may end up thinking that chemistry is simply a math problem - which it definitely is not.
Unit factors may be made from any two terms that describe the same or equivalent "amounts" of what we are interested in. For example, we know that
1 inch = 2.54 centimeters Note: Unlike most English-Metric conversions, this one is exact. There are exactly 2.540000000. centimeters in 1 inch.
We can make
two unit factors from this information:
Now, we can solve some problems. Set up each problem by writing down what you need to find with a question mark. Then set it equal to the information that you are given. The problem is solved by multiplying the given data and its units by the appropriate unit factors so that only the desired units are present at the end.
(1) How many centimeters are in 6.00 inches?
(2) Express 24.0 cm in inches.
You can also string many unit factors together.
(3) How many seconds are in 2.0 years?
Scientists generally work in metric units. Common prefixes used are the following: