1. Significant Digits and Rounding (A review)
Chemistry 11
Ms. McGrath

2. Significant Digits Measurements have uncertainty due to:
measuring device
a person’s inability to perceive and interpret a reading
The last (farthest right) digit is always an estimate.

3. Rules for determining significant digits
All non-zeros are significant
7886 has _____ s.d.
19.4 has _____ s.d.
_____ s.d.

4. Rules for determining significant digits
All zeros that are located between two non-zero numbers are significant
408 has _____ s.d.
25074 has _____ s.d.
10203 has _____ s.d.

5. Rules for determining significant digits
Zeros that are located to the left of a measurement are not significant
has _____ s.d.
has _____ s.d.
0303 has _____ s.d.

6. Rules for determining significant digits
Zeros located to the right of a measurement may or may not be significant
22700 has _____ s.d.
has _____ s.d. (because of decimal)

7. Significant Digits and Calculations
Final answers must not imply more certainty than measured quantities

8. Significant Digits and Calculations
Rule 1 – Multiplying and Dividing
The value with the fewest number of significant digits, going into a calculation, determines the number of significant digits that you should report in your answer.

9. Significant Digits and Calculations
Rule 2 – Adding and Subtracting
The value with the fewer number of decimal places, going into a calculation, determines the number of decimal places that you should report in your answer.

10. Significant Digits and Calculations
Rule 3 – Rounding
To get the appropriate number of significant digits (Rule 1) or decimal places (Rule 2), you may need to round your answer.
1. if your answer ends in a number that is greater than 5, increase the preceding digit by 1.
ex is rounded to 2.35
2. if your answer ends with a number that is less than 5, leave the preceding number unchanged.
ex is rounded to 5.7

11. Significant Digits and Calculations
3. if your answer ends with 5, increase the preceding number by 1 if it is odd. Leave the preceding number unchanged if it is even.
ex can be rounded to 18.4
ex can be rounded to 18.2