1. Chapter 3 Scientific Measurement
Full screen view – click screen in lower right corner (Internet Explorer 4.0 & higher)

2. Measurements 2 types: Qualitative measurements (words)
Heavy, hot, or long
Quantitative measurements (#’s) & depend on:
Reliability of measuring instrument
Care w/ which it’s read – determined by YOU!
Scientific Notation
Coefficient raised to power 10
(ex. 1.3 x 107)
Review: Textbook pages R56 & R57

3. Accuracy, Precision, and Error
Necessary for reliable lab measurements
Accuracy –
Precision –
Reproducible
For #’s w/ decimal pt……… decimal place right-most digit is in
134.90
0.0157
how close measurement is to true value
how close measurements to each other

4. Accuracy, Precision, and Error
For #’s w/o decimal pt…...right- most non-zero #
34200
120390

5. Precision and Accuracy

6. Accuracy, Precision, and Error
Accepted value – based on reliable references (Density Table page 90)
Experimental value - measured in lab

7. Accuracy, Precision, and Error
NFL Flyovers 4:53
Error = accepted value – experimental value
can be + or -
Percent error = absolute value of error divided by accepted value, & multiplied by 100%
| error |
accepted value
x 100%
% error =

8. Significant Figures in Measurements
Significant figures all known digits + one estimated digit
Measurements must be recorded to correct # sig figs

9. Figure 3.5 Significant Figures - Page 67
Which measurement is the best?
What is the measured value?
What is the measured value?
What is the measured value?

10. Rules for Counting Sig Figs
Non-zeros always count as sig figs:
3456 has
4 sig figs

11. Rules for Counting Sig Figs
Zeros
Leading zeroes do not count as sig figs:
has
3 sig figs

12. Rules for Counting Sig Figs
Zeros
Captive zeroes always count as sig figs:
16.07 has
4 sig figs

13. Rules for Counting Sig Figs
Zeros
Trailing zeros significant only w/ written decimal point:
9.300 has
4 sig figs

14. Rules for Counting Sig Figs
Two special situations have unlimited # sig figs:
1. Counted items
23 people, or 425 thumbtacks
2. Exactly defined quantities
60 minutes = 1 hour
Big Sig Fig Gig (2:27) – Mark Rosengarten

15. Sig Fig Practice #1 How many significant figures in the following?
5 sig figs
17.10 kg 
4 sig figs
100,890 L 
5 sig figs
These all come from some measurements
3.29 x 103 s 
3 sig figs
cm 
2 sig figs
3,200,000 mL 
2 sig figs
This is a counted value
5 dogs 
unlimited

16. Sig Figs in Calculations
answer cannot be more precise than least precise measurement.
Sometimes, calculated values need rounded off

17. Rounding Calculated Answers
Decide how many sig figs needed
Round to that many digits, counting from the left
Is next digit less than 5? Drop it.
Is next digit 5+? Add 1

18. - Page 69
Be sure to answer the question completely!

19. Rounding Calculated Answers
Addition and Subtraction
answer rounded to same # decimal places as least # decimal places in problem

20. - Page 70

21. Rounding Calculated Answers
Multiplication and Division
answer rounded to same # of sig figs as least # of sig figs in problem

22. - Page 71

23. Rules for Sig Figs in Mathematical Operations
Multiplication and Division: # sig figs in result = # in least precise measurement used in calculation.
6.38 x 2.0 =
12.76  13 (2 sig figs)

24. Sig Fig Practice #2 Calculation Calculator says: Answer 3.24 m x 7.0 m
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 x 2.87 mL
g/mL
2.96 g/mL

25. Rules for Sig Figs in Mathematical Operations
Addition and Subtraction: # decimal places in result = # decimal places in least precise measurement. =
 (3 sig figs)

26. Sig Fig Practice #3 Calculation Calculator says: Answer 3.24 m + 7.0 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
*Note the zero that has been added.

27. International System of Units p. 73
Measurements depend on units
The standards of measurement of science is Metric System
Why science uses the metrics 2:30

28. International System of Units
Metric system now revised & named International System of Units (SI), (1960)
multiples of 10
5 common base units in chemistry
meter, kilogram, kelvin, second & mole

29. Nature of Measurements
Measurement - quantitative observation -2 parts:
Part 1 – number
Part 2 - unit
Examples:
22 grams
3.55 x 103 moles

30. International System of Units
Sometimes, non-SI units used
Liter, Celsius, calorie
Derived units
joining units
Speed = kilometers/hour (distance/time)
Density = grams/mL (mass/volume)

31. SI basic unit - meter (m) distance btwn 2 objects
Length
SI basic unit - meter (m)
distance btwn 2 objects
use prefixes for larger/smaller units

32. SI Prefixes – Page 74 - Common to Chemistry
Abbreviation
Meaning
Exponent
Mega- M
Million
106
Kilo- k
thousand
103
Deci- d
tenth
10-1
Centi- c
hundredth
10-2
Milli- m
thousandth
10-3
Micro- 
millionth
10-6
Nano- n
billionth
10-9
Pico- P
trillionth
10-12

33. Volume Space occupied by matter
Calculated for solid…length x width x height
derived from units of length
SI unit = cubic meter (m3)
Everyday unit = Liter (L), non-SI
(Note: 1mL = 1cm3)

34. Devices for Measuring Liquid Volume
Graduated cylinders
Pipets
Burets
Volumetric Flasks
Syringes

35. Volume Changes!
Volumes of a solid, liquid, or gas generally increases w/ temp
More prominent for GASES
Therefore, measuring instruments calibrated for specific temp
usually 20 oC, which is about room temp
Ex. Volumetric flask

36. Mass - quantity of matter present
Units of Mass
Mass - quantity of matter present
Mass constant, regardless of location
Weight - force of “g”- changes w/ location

37. SI unit - kilogram (kg) Working with Mass everyday unit is gram (g)
measuring instrument: triple beam balance

38. Units of Temperature Temp - measures how hot/cold object is.
Heat moves from hi - low temp
2 temp scales:
Celsius – named after Anders Celsius
Kelvin – named after Lord Kelvin
(Measured with a thermometer.)

39. Units of Temperature Celsius scale Water Freezing point = 0 oC
Water Boiling point = 100 oC
Kelvin scale does not use degree sign, just K
absolute zero = 0 K (no negative values)
formula to convert: K = oC + 273

40. - Page 78

41. Energy - ability to do work, or produce heat energy can be measured
Units of Energy
Energy - ability to do work, or produce heat
energy can be measured
2 common units:
Joule (J) = SI unit of energy, named after James Prescott Joule
calorie (cal) = heat needed to raise 1g of water 1 oC

42. Units of Energy
Conversions btwn joules & calories carried out by using following relationship:
1 cal = J

43. Sec 3.3 Conversion factors
A “ratio” of equivalent measurements
Start with two things that are the same:
one meter is one hundred centimeters
write it as an equation
1 m = 100 cm
Divide on each side of equation to come up with 2 ways of writing the number “1”

44. Conversion factors
100 cm
1 m =
100 cm

45. Conversion factors
1 m = 1
100 cm

46. Conversion factors
1 m = 1
100 cm
100 cm =
1 m
1 m

47. Conversion factors
1 m = 1
100 cm 1 =
100 cm
1 m

48. big # small unit = small # big unit
Conversion factors
unique way of writing the # 1
In same system they are defined quantities so unlimited number of sig figs
big # small unit = small # big unit
100 cm = 1 m

49. Practice writing two possible conversion factors for the following:
Between kilograms and grams
between feet and inches
using qt. = 1.00 L

50. What are they good for?
We can multiply by # “one” creatively to change units
Question: 13 inches is how many yards?
We know that 36 inches = 1 yard
1 yard = inches
13 inches x yard = inches

51. What are they good for?
We can multiply by a conversion factor to change the units .
Problem: 13 inches is how many yards?
Known: 36 inches = 1 yard.
1 yard = inches
13 inches x yard = 0.36 yards inches

52. Dimensional Analysis
Method of analyzing & solving problems, by using units (dimensions) of measurement
Dimension = unit (g, L, cm)
Analyze = solve
Using units to solve problems
If units of answer correct, you probably did math correctly!

53. Dimensional Analysis
provides alternative approach to problem solving, instead of with equation or algebra.
ruler is 12.0 inches long. How long is it in cm? ( 1 inch = 2.54 cm)
How long is this in meters?
A race is 10.0 km long. How far is this in miles, if:
1 mile = 1760 yards
1 meter = yards

54. p. 82 practice problem #28
How many minutes are there in exactly one week?

55. p. 83 practice problem # 30
An experiment requires that each student use an 8.5-cm length of magnesium ribbon. How many students can do the experiment if there is a 570- cm length of magnesium ribbon available?

56. Converting Between Units
measurements with one unit converted to equivalent measurement with another unit easily solved using dimensional analysis
Sample: Express 750 dg in grams.
Many complex problems are best solved by breaking the problem into manageable parts.

57. p. 84 practice problem #32
Using tables from this chapter, convert these: a km to meters b. 4.6 mg to grams c g to centigrams

58. Converting Between Units
Let’s say you need to clean your car:
Start by vacuuming the interior
Next, wash the exterior
Dry the exterior
Finally, put on a coat of wax
What problem-solving methods can help you solve complex word problems?
Break the solution down into steps, and use more than one conversion factor if necessary

59. p. 85 practice problem # 34 (p. 30 in workbook)
The radius of a potassium atom is nm. Express this radius in the unit centimeters.

60. Converting Complex Units?
Complex units are those that are expressed as a ratio of two units:
Speed might be meters/hour
Sample: Change 15 meters/hour to units of centimeters/second
How do we work with units that are squared or cubed? (cm3 to m3, etc.)
BONUS: Crash of Flight 143 – see my webpage

61. - Page 86

62. Section 3.4 Density
Which is heavier- a pound of steel or a pound of styrofoam?
Most people answer “steel”, but the weight is exactly the same
They are normally thinking about equal volumes of the two
The relationship here between mass and volume is called Density

63. Density The formula for density is: mass volume
Common units are: g/mL, or g/cm3, (or g/L for gas)
Density is a physical property, and does not depend upon sample size
A gold nugget has the same density as a gold bar
Density =

64. Note temperature and density units
- Page 90

65. Density and Temperature
What happens to the density as the temperature of an object increases?
Mass remains the same
Most substances increase in volume as temperature increases
Thus, density generally decreases as the temperature increases

66. Density and Water
Water is an important exception to the previous statement.
Over certain temperatures, the volume of water increases as the temperature decreases (You don’t want your water pipes to freeze in the winter, right?)
Why does ice float in liquid water?

67. - Page 91

68. - Page 92