Chapter 2 Standards of Measurement

1
Chapter 2Standards of Measurement

• Objectives
• Understand Mass and Weight (2.1)
• Identify the metric units of measurement (2.6)
• Explain what causes uncertainty in measurements
  (2.7, 2.8 2.12)
• Learn how to use significant digits and
  scientific notation (2.2 2.5)
• Dimensional Analysis (2.8)
• Density (2.12)

2
The Metric System (2.6)The International System
of Units

• Standards of measurement
• Base units (7) see Table 2.2 (pg 20)
• MASS
• LENGTH
• TIME
• COUNT, QUANTITY
• TEMPERATURE
• ELECTRIC CURRENT
• LUMINOUS INSTENSITY

3
The Metric System

• Derived Units
• AREA
• VOLUME
• ENERGY
• FORCE
• PRESSURE
• POWER
• VOLTAGE
• FREQUENCY
• ELECTRIC CHARGE

4
The Metric System

• Metric Prefixes make base unit larger or
  smaller
• Table 2.1 must know bolded prefixes
• Based on 10
• Math method vs. Stairs

5
Conversion Practice

• Convert a volume of 12 microliters into
  centiliters
• Express a distance of 15 meters in kilometers
• Which is the longer amount of time, 1351 ps or
  1.2 ns?

6
Uncertainty in Measurement

• Why are digits in measurements uncertain?
• Instruments never completely free of flaws
• Always involves estimation
• Choose the right instrument for the job
• May be estimated for you (electronic scales)
• Scale is marked but you estimate the in-between

7
Uncertainty in Measurement

• Precision
• Accuracy

8
Significant Digits

• All digits known with certainty plus one final
  digit which is uncertain (or estimated)
• All non-zeros are significant (143.34)
• A zero is significant when
• It is between nonzero digits (2004)
• A zero is not significant when

9
Significant Digits - PRACTICE

• How many significant digits?
• 54.23
• 23.00005
• 0.0004
• 35000
• 0.000504
• 45.623200
• 5,000,000
• 4,000,000.1

10
Significant Digits - Calculations

• Addition and Subtraction
• Round answer to have final digit in the SAME
  PLACE as the last digit in the LEAST ACCURATE
  MEASUREMENT
• 1.21 5.002 10.
• 34.5 12.45 23.0505
• 186.31 11.1
• 12.0231 3.86
• 0.100012 120.
• 1200 12 15 0.5

11
Significant Digits - Calculations

• Multiplication and Division
• The answer has as many sig figs as the number
  with the
• 14.8 x 3.1
• 18.2 x 3.0
• 52/1.5
• 321.868783 x 1
• 2400 x 2.123
• 15000/12.354

12
Scientific Notation

• Convenient way of writing very large or very
  small numbers and showing only significant
  figures
• Number between
• 5120 becomes
• Move decimal point in original number to make
  number
• Move left move right

13
Scientific Notation Practice

• 123,000
• 0.000045
• 23.45
• 0.0000000003
• 1,000,000

14
Scientific Notation

• Adding and subtracting
• Numbers must be the SAME POWER
• 1.4 x 104 2.1 x 105 (must change to 21.0 x 104)
  and then
• 3.2 x 103 1.8 x 102

15
Scientific Notation

• Multiplying
• (2.0 x 103) x (3.0 x 104)
• Dividing
• (8.2 x 108) / (4.1 x 104)

16
Types of Measurements

• Mass amount of matter in a body
• Weight measure of earths gravitational
  attraction for that object

17
Types of Measurements

• Volume the amount of space occupied by matter
• Temperature measure of the intensity of heat
  (figure 2.6)

18
Conversion Factors

• Enable movement between metric system and
  English system
• See back cover of book and Appendix III
• Common conversions you should memorize

19
Dimensional Analysis(Problem Solving)

• Remember
• A technique of converting between units

20
Dimensional Analysis(Problem Solving)

• Conversion Factors ratio derived from the
  equality between 2 different units
• CF can be written either way

21
Dimensional Analysis(Problem Solving)

• The t method

Conversion Factor
22
Dimensional Analysis(Problem Solving)
Dimensional Analysis(Problem Solving)
How many seconds are in 4.15 hours?
If a student needs 1.5 mL of water, how many cups
does he need?
23
Density

• Common ratio used in chemistry
• Physical property of a substance
• Mass/volume
• D m
• v
• SI units kg/m3

• Solid
• g/cm3
• Liquid
• g/mL
• Gas
• g/L

Can change due to temperature and/or pressure
changes
24
Density

• Find the density of a piece of metal with a
  volume of 2.7 cm3 and a mass of 10.8 g.

2. Determine the mass of an object with a density
of 0.24 g/cm3 and a volume of 2 cm3.
!!!