Untitled - Kelly Walsh High School

6 CHEMISTRY FOR THE UTTERLY CONFUSED
Don’t Forget!
2. For multiplication and division problems, round off the answer to the same
number of significant figures in the measurement with the fewest significant
figures.
7.253 m 3.52 m 25.53056 m 2 25.5 m 2 (rounded to three
significant figures)
In this book, we will tend to be very strict in rounding off the final answer to the
correct number of significant figures. Your instructor will tell you just how strict
she or he wishes you to be.
Carry as many numbers as possible throughout the calculation and only round
off the final answer.
1-4 Utterly Confused About
Problem Solving
In this section, we will introduce one of the two common methods for solving
problems. (You will see the other method in Chapter 5.) This is the Unit
Conversion Method. It will be very important for you to take time to make sure
you fully understand this method. You may need to review this section from
time to time. The Unit Conversion Method, sometimes called the Factor-Label
Method or Dimensional Analysis, is a method for simplifying chemistry problems.
This method uses units to help you solve the problem. While slow initially,
with practice it will become much faster and second nature to you. If you use
this method correctly, it is nearly impossible to get the wrong answer. For practice,
you should apply this method as often as possible, even though there may
be alternatives.
Let’s use the question of “How many feet are in 3.5 mi?” to illustrate how to apply
the Unit Conversion Method. First, we will organize the information by writing
the given value (3.5 mi) and the unit for the answer, separated by an equals sign.
3.5 mi ? ft