NAME  _____________________                       DATE  ____________________

 

CHEM 121 Practice with Significant Figures

 

Read sections A.3, A.4, and A.5 of Appendix A of your text (pages A.6 – A.12).  Apply what you read by completing the following problems.  The answers are given below.  (Not all answers are given in both scientific notation and floating decimal format, but either format is acceptable.)

 

For credit, you must show and explain each step in which you make a decision regarding significant figures.  Your answers should look like the solution shown in the example below.

 

As you complete the problems, remember there are two separate rules to consider for reporting significant figures after calculations.  One rule applies to multiplication and division.  The other applies to addition and subtraction.  If more than one mathematical step is incorporated in a calculation, you must consider the correct number of significant figures after each mathematical step.  This has been done to achieve the answers given here; however, these answers have not been rounded until the final step (see the bottom of page A.8 and the example below). 

 

After you have the read the Appendix, if you are uncertain how to complete these problems correctly, please see your lecture or laboratory instructor or attend a chemistry help session for assistance.

 

Example problem:   (25.7 +  32.15)/12

 

Solution:

 

Step 1:  Add:  25.7 + 32.15 = 57.85

            Apply sig fig rule for addition:  First number has 1 sig fig after the decimal

                                    Second number has 2 sig figs after the decimal

                                    Least number of decimal places is 1 sig fig after the decimal

                                    Thus, we keep 1 sig fig after the decimal à  57.85

(I have underlined where the last sig fig should be, but I have not rounded yet because I have not completed all math steps.)

 

Step 2:  Divide result of Step 1 by 12

            57.85/12 = 4.820833333

Apply sig fig rule for division:  First number has 3 total sig figs (For 57.85, remember, the sig figs in this number really stop at the underlined 8)

                                    Second number has 2 total sig figs

                                    Least total number of sig figs is 2

                                    Thus, we keep 2 total sig figs in our answer à 4.8

 

            Final Answer:  4.8

                                                           

 

PROBLEMS:

1.  6.512  + 5.29                                           

 

 

 

 

 

Final Answer:  __________

2.  (6.78 x 10-4)  x (1.4 x 102)

 

 

 

 

 

Final Answer:  __________

3.  12.5 x 75                                                  

 

 

 

 

 

Final Answer:  __________

4.  9.651 x 102 + 8

 

 

 

 

 

 

 

Final Answer:  __________

5.  14.3 + (12.2 x 2.0)                                              

 

 

 

 

 

 

 

 

Final Answer:  __________

6.  25.6789 - 2.57

 

 

 

 

Final Answer:  __________

7.  (6.432 x 102  +  8.342 x 101)/2.143                   

 

 

 

 

 

 

 

 

 

Final Answer:  __________

8. (6.432 x 102  +  8.342 x 101)/2.14

 

 

 

 

 

 

 

 

 

 

 

Final Answer:  __________

9.  12.785 - 9.43                                           

 

 

 

 

 

 

 

Final Answer:  __________

10.  0.243 - 0.24

 

 

 

 

 

 

 

 

Final Answer:  __________

 

 

Answers

1.  11.80                       2.  9.5 x 10-2                  3.  940 or 9.4 x 102         4.  973              5.  39

6.  23.11                       7.  339.1                       8.  340 or 3.40 x 102       9.  3.36             10.  0.00