1. Scientific Measurement
Chapter 3
Scientific
Measurement

2. Steps in the Scientific Method
Observations
- quantitative
- qualitative
Formulating Hypotheses
- possible explanation for the observation
Performing Experiments
- gathering new information to decide
whether the hypothesis is valid

3. Nature of Measurement Measurement - quantitative observation
consisting of 2 parts
Part 1 - number
Part 2 - scale (unit)
Examples:
20 grams
6.63 x Joule seconds

4. The Fundamental SI Units
(le Système International, SI)

5. SI Prefixes Common to Chemistry
Unit Abbr.
Exponent
Mega M
106
Kilo k
103
Deci d
10-1
Centi c
10-2
Milli m
10-3
Micro 
10-6
Nano n
10-9
Pico p
10-12

6. Uncertainty in Measurement
A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.
Measurements are performed with
instruments
No instrument can read to an infinite
number of decimal places

7. Precision and Accuracy
Accuracy refers to the agreement of a particular value with the true (known) value.
Precision refers to the degree of agreement among several measurements made in the same manner. (aka – reproducibility)
Neither accurate nor precise
Precise but not accurate
Precise AND accurate

8. Rules for Counting Significant Figures
If the number contains a decimal, count from right to left until only zeros or no digits remain.
Examples: grams
4 sig figs
meters
5 sig figs
grams
2 sig figs

9. 2. If the number does not contain a decimal, count from left to right until only zeros or no digits remain. Examples: 255 meters 3 sig figs 1,000 kilograms 1 sig fig

10. Exact numbers have an infinite number of significant figures.
1 inch = 2.54 cm, exactly

11. Sig Fig Practice #1 1.0070 m  5 sig figs 17.10 kg  4 sig figs
How many significant figures in each of the following?
m 
5 sig figs
17.10 kg 
4 sig figs
100,890 L 
5 sig figs
3.29 x 103 s 
3 sig figs
cm 
2 sig figs
3,200,000 
2 sig figs

12. Rules for Significnt Figures in Mathematical Operations
Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement. =
 18.7 (3 sig figs)

13. Sig Fig Practice #2 Sig Fig Practice #2 Calculation Calculator says:
Answer
3.24 m m
10.24 m
10.2 m
100.0 g g
76.27 g
76.3 g
0.02 cm cm
2.391 cm
2.39 cm
713.1 L L L
709.2 L
lb lb lb lb
2.030 mL mL
0.16 mL
0.160 mL

14. Rules for Significant Figures in Mathematical Operations
Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation.
6.38 x 2.0 =
12.76  13 (2 sig figs)

15. Sig Fig Practice #3 Sig Fig Practice #3 Calculation Calculator says:
Answer
3.24 m x 7.0 m
22.68 m2
23 m2
100.0 g ÷ 23.7 cm3
g/cm3
4.22 g/cm3
0.02 cm x cm
cm2
0.05 cm2
710 m ÷ 3.0 s
m/s
240 m/s
lb x 3.23 ft
lb·ft
5870 lb·ft
1.030 g ÷ 2.87 mL
g/mL
2.96 g/mL

16. Converting Celsius to Kelvin
Kelvin = C + 273
°C = Kelvin - 273

17. Dimensional Analysis aka: factor label fence-post
unit cancellation
fence-post
provides a systematic way of solving numerical
problems
Set-up: Given Desired Units___
Units to Eliminate

18. Dimensional Analysis Examples
115 lbs = ______ g
115 lbs g  x 104 g lb OR
115 lbs x g lb

19. Useful Conversions 1 mi = 1.6093 km 1 lb = 453.59 g 1 L = 1.0567 qt
1 in = 2.54 cm
0F = (9/5) 0C + 32
1 L = qt
1 mL = 1cm
1 kg = lb
0C = (5/9)( 0F – 32 ) 3