Scientific Measurement
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David Chan
Northwestern University
Today (Day Eight)
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(0-15) Discuss Test (0-15)
(15-20) Discuss Test Resubmittal Process (15-20)
Chapters 2+3 Syllabus
(20-35) Qualitative vs. Quantitative (20-35)
Accuracy vs. Precision
(35-43) Class Jobs
(0-15) Website intro, online grades
(15-30) Scientific Notation (35-43)
(30-43) Popsicle sticks match game
Scientific Measurement
• Questions to Ponder:
– Why is measurement important?
– What are the different types of
measurement?
– What is the history of measurement?
– What do you know already?
– What do you think we will focus on when
studying measurement?
Types of Measurements
Types of Measurements
3
140
6
350
868
Types of Measurements
Types of Measurement
Types of Measurements
• Qualitative Measurements
– Descriptive, nonnumerical form
• Quantitative Measurements
– Definite form, numbers and units
• Examples:
– Basketball is brown
– Diameter of basketball is 31 cm
– Air pressure in the basketball is 12 psi.
– Surface of basketball has indented seams.
Accuracy, Precision, and Error
• Accuracy – how close to actual or true value
• Precision – how close measurements are to one
another
• Dartboard analogy
• Examples
– Precision or accuracy?
• Multiple measurements
• Correct
• Repeatable
• Reproducible
Converting Measurements to Scientific Notation
• Useful for large and small numbers
• 2 numbers: Coefficient + 10 raised to power
• Addition and Subtraction
– Exponents must be same to add coefficients
• Multiplication
– Multiply coefficients and add the exponents
• Division
– Divide coefficients and subtract exponents
• EE button on calculator
• Practice Problems #4
Examples:
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91.4m
0.000000000154 m
6378000 m
0.000008 m
149600000000 m
Today (Day Nine)
• (0-15) Cat’s Meow – qualitative observations
• (15-25) Significant Figures
– Paper rulers
• (25-35) SI Units – Length, Volume, Mass
• (35-43) Discuss HW – clock buddies
Significant Figures
• Important when making measurements in
experiments
• All digits known with certainty plus one estimated
or uncertain digit
Rules/Examples
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1) 24.7m (3)
2) 7003 m (4)
3) 0.0071 m (2)
4) 25.0 (3)
5) 27,210 m (4)
Rules Explained
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1) Nonzero digits are always significant (24.7m)
2) Zeroes in between are significant (7003m)
3) Left zeroes are not significant (0.0071 m)
4) Right zeroes are significant (25.0 m)
5) Right zeroes left of understood decimal are not
sig.(27,210m)
• 6) Unlimited sigfigs
– Counting, exact quantities (60min=1hr)
• Practice Problems #5,6
More Rules
• Rounding: answers cannot be more precise than
least precise measurement from which it was
calculated
• Rounding: greater than 5, less than 5
• Add/Subtract: round to least significant place
• Mult/Divide: round to same # as least number of
sigfigs
• Practice Problems #11,12
SI units and Prefixes
• International System of Units (SI)
• SI Base Units (table 2.1)
– Length, Mass, Temp, Time
• SI Unit Prefixes
– Table 3.3
• Derived Units
– Density, volume
Length
• Basic SI unit = meter
• Common: millimeters, centimeters, kilometers
• Running races: 5K, 10K
Volume
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Derived unit: cubic _____meters
CC’s = cubic centimeters
1 CC = 1ml
1 cubic decimeter = 1L
Volumetric flasks, graduated cylinders
Mass vs. Weight
• Mass – amount of matter (1 kg)
• Weight – force on mass by gravity (Physics)
Today (Day 10)
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(0-5) Opener – sci notation
(5-15) Density
(15-20) Density Demo: How Sweet It is!
(20-25) Temperature
– Making thermometers?
• (25-30) Percent Error
– Activity
• (30-35) Discuss HW – clock buddy
Calculating Density
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Density = Mass/Volume
Characteristic of substance
Water displacement technique
Temperature increases, V increases, Density
decreases
• Density of Common substances (table 2.8)
• Practice Problems #23,24
• Examples:
– Volume = 245 cm3 and mass of 612 g. Is it
aluminum?
– density of gold = 19.3 g/cm3. What is volume
Specific Gravity
• Comparison of density of substance with density
of reference, usually at same temp.
• Specific Gravity = density of substance/density of
water
Converting Celsius and Kelvin
• Temperature
– Determines direction of heat transfer
• Thermal expansion
– Generally expand as temp increases
– Generally contracts as temp decreases
• Celsius – history
• Kelvin = -273.15 C = 0 K
– Accounts for absolute zero (-273.15C)
• Examples
– 170 Celsius to Kelvin
Percent Error, Experimental Error
• Accepted value – correct value established by
references
• Experimental Value – measured in lab
• Error: accepted – experimental
• Percent Error: error/accepted x 100%
• Example
– Estimated volume = 200 mL
– Accepted volume = 208 mL Calc Percent error
Today (Day 11)
• (0-10) Discuss HW – jigsaw (0-10)
• (10-15) Class Jobs (10-15)
• (15-20) How to Write Lab Reports, Sample
Reports (15-20)
• (20-30) PreLab: Observing Chemical Changes
– 4 more safety rules
• (30-43, 0-20) Lab: Observing Chemical Changes
• (20-43) Prep Debate (20-43)
Today (Day 12)
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(0-5) discuss HW answers
(5-10) Review Debate
Reading Volumes Demo
(10-40) Debate
(40-43) Review for Quiz
Today (Day 13)
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(0-10) Opener – sigfig/equipment activity
(10-15) Review Debate/Labs – Peer review
(15-20) Demo – Can You Pour a Gas?
(20-35) Quiz
(35-43) PreLab
(0-43) Lab – Density
POURING CARBON DIOXIDE.
• Construct a series of three 5-cm steps that will fit
into a wide mouth jar. Set a lighted candle on each
step. Slowly pour carbon dioxide gas from an
open container into the jar. Carbon dioxide is
heavier than air. As it settles it extinguishes the
candles one by one starting with the candle at the
lowest level. There are many ways to generate
carbon dioxide. Try mixing some vinegar with
bicarbonate of soda. [HG]
Today (Day 14)
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(0-10) discuss quiz
(10-20) Discuss lab
(20-35) Problem Solving
Conversion Factors - list
(35-43) Powers of Ten Website/Video
Converting between units
Dimensional Analysis – Converting Units
• Write starting quantity
• Write conversion factors
– Numerator: What are you trying to convert
into?
– Denominator: What are you converting from?
– Which one is bigger? = 1
– How many does it equal?
• 1 m = 100 cm
• 1000 m = 1 km
List of Unit Prefixes
• Powers of ten Java
– http://micro.magnet.fsu.edu/primer/java/sci
enceopticsu/powersof10/
• List of 20:
– http://physics.nist.gov/cuu/Units/prefixes.ht
ml
• Common ones:
– http://lamar.colostate.edu/~hillger/common.
htm
• Prefixes revisited
– http://www.wordwizz.com/pages/10exp0.ht
Practice
– 0.044 km to meters
– 860 mg to grams
– 6.7 s to milliseconds
Today (Day 15)
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(0-5) Opener
(5-10) Discuss HW
(10-15) Multistep, Complex Units
(15-43) Stations Activity – Converting Units
Multistep Problems
• Use more than one conversion factor
• Examples:
– 261 nm to millimeters
– 642 cg to kilograms
Complex Units
• Areas, Volumes, Speeds
• Examples:
– 55 mph to m/s
– 1.54 kg/L to grams per cubic centimeter
Today (Day 16)
• Peer Review – Density Labs (20 min)
• Review for Test (30-40 min)
Today (Day 17)
• Test (40-60 min)
Intro to Labs
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Lab Report Format
Lab Safety
Lab Notebooks
Lab Preps
Lab #1: Chemical and Physical Changes
• Objectives:
– Chemical and physical properties
– Chemical and physical changes
– Become acquainted with lab facilities
• Lab Techniques:
– Filtration/Evaporation
– Bunsen Burners
– General Lab Procedures:
• Supplies/Cleaning
• Contamination of materials
• Dissolving small quantities
Exit Slips
• On a separate sheet of paper labeled “Exit Slip”,
please include the following:
• 1 thing you learned today
• 1 thing that still confuses you
• Any other comments about the pace, methods, etc.
• Thank you!