Chemistry 3.1 Notes (Accuracy, precision, error and sig figs).ppt

Chemistry 1

1. Chemistry 3.1
Uncertainty in
Measurements

2. I. Accuracy, Precision, & Error
A. Accuracy – how close a measurement
comes to the “true value”.
1. Ex: Throwing Darts
true value = bull's-eye

3. B. Precision – how close a series of
measurements are together.
1. Ex: Throwing Darts

4. C. Pg. 64 Explanation
Poor Accuracy
Good Precision
Good Accuracy
Good Precision
Poor Accuracy
Poor Precision

5. D. Error – the difference between the
accepted value and the experimental
value.
1. Formula –
2. Error = ex. value – accepted value
| error |
accepted value

6. E. Examples
1. In class you determine the melting
point of salt is 755 deg C. The actual
value is 805 deg C. What is your
percent error?
 [|755 - 805| / 805] x 100 =
 6.2% error

7. II. Significant Figures
A. Def – all digits known plus one
estimated one.
1. Measurements must be recorded with
significant figures.

8. 2. Rules (pg.66)
-All other numbers are significant
-zeros may or may not be significant
-leading zeros are not significant
 0.02 1 (sig fig)
-captive zeros are significant
 0.0203 3 (sig figs)
-trailing zeros following the decimal
point are significant
 0.02030 ? (sig figs)
 200 ? (sig figs)
 200.0 ? (sig figs)
4
1
4

9. 3. Rounding with Sig Figs
-Express the following #’s to 3 sig figs
 421798.076
= 422,000
 0.00099985
= .00100
 1
= 1.00
 8222
= 8,220
 0.42
= .420

10. 4. Scientific Notation + Sig figs
A. All #’s in scientific notation are
counted as significant figures.
B. Ex:
3.0200 x 10
3
= sig figs
2.77 x 10
6
= sig figs
5
3

11. 5. Adding and subtracted
A. The answer must not contain any sig
figs beyond the place value common to
all #’s
B. Ex: 4.8
+ 2.015
6.8
(not 6.815)

12. 6. Multiplication and Division
A. The answer must not contain more
sig figs than the least # of sig figs.
B. Ex: 3.1
x 4.01
12
(not 12.431)

13. In Class Problems
1. How many sig figs?
-123 meters -30.0 meters
-40,506 kg -6.455 x 10
3
kg
2. 3.45 + 9.001 and 4.22 - 9.0
3. 3.4 x 5.345 and 10.7 / 12.75
4. 6.33 x 10
3
+ 5.1 x 10
4