Chapter 2: Measurement and Problem Solving
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Transcript of Chapter 2: Measurement and Problem Solving
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CHAPTER 2: MEASUREMENT AND PROBLEM SOLVING
16 days
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First day of school Lab safety
Day One
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Syllabus HIGHLIGHTS!!!
Expectations Be Prepared NO FOOD OR DRINK IN THIS
CLASSROOM EVER!!! How do I get a good grade? Hall Passes Absences
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MISCELLANEOUS BOOKS: Put name in front cover and please
cover the book!
Three ring binder
Calculator
Lab Safety Contract
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Lab Notebook
Labs Spiral bound notebookLab procedure: found online and in the room Must be written in your lab notebook before you
begin lab as well as any data tables you may need
Completed with a partner but must be a collaborative effort
Each partner is responsible to have the data before they leave the room
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Lab Safety Video
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Location of Safety Equipment Goggles Aprons Sand Eyewash station Safety Shower MSDS Sheets
Fire Blanket Fire extinguisher Emergency Stop
Button Fire Alarm Fume hood Broken Glass
Container Assignment: Draw a diagram of the room and label the safety equipment listed above.
Explain what each of the above is used for and when they are used.
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WebsitesMeasurements & Scientific
Notation
Day Two
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Two websites you will be using all year!!! www.nordoniahonorschemistry.wikispac
es.com Class website Lab manual Calendar Lecture Notes Answer Keys to Homework
www.masteringchemistry.comAdditional Reviews and assignments
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What Is a Measurement?
Quantitative observation
Comparison to an agreed upon standard
Every measurement has a number and a unit
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A Measurement
The unit tells you to what standard you are comparing your object.
The number tells you:1.What multiple of the standard the object
measures.
2. The uncertainty in the measurement.
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Scientists have measured the average global temperature rise over the past century to be 0.6 °C
°C tells you that the temperature is being compared to the Celsius temperature scale.
0.6 tells you that:1. The average temperature rise is 0.6
times the standard unit of 1 degree Celsius.
2. The confidence in the measurement is such that we are certain the measurement is between 0.5 and 0.7 °C.
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Scientific Notation
We should all be familiar with this but I just want to remind you of a few things!!!
S.N. is an easy way to express VERY large or VERY small numbers
Chemistry most of the time deals with extremely small number considering we talk about atoms!
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3 parts to S.N.
1.2 X 10-9
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How to Express a number in Scientific Notation
1. Move the decimal point to obtain a number between 1 and 10.
2. Write the result from Step 1 multiplied by 10 raised to the number of places you moved the decimal
** The exponent is POSITIVE if you moved the decimal to the LEFT
** The exponent if NEGATIVE if you moved the decimal to the RIGHT
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Practice—Write the Following in Scientific Notation
123.4
145000
25.25
1.45
8.0012
0.00234
0.0123
0.000 008706
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Practice—Write the Following in Standard Form2.1 x 103
9.66 x 10-4
6.04 x 10-2
4.02 x 100
3.3 x 101
1.2 x 100
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Metric and Factor Label
Day Three
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Metric System
Group of units used to make any kind of measurements
Best known for its simpleness Why is it so simple?
Used all around the world with scientists
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The Standard Units Scientists generally report results in an
agreed upon International System. The SI System
Aka Système International
Quantity Unit SymbolLength meter mMass kilogram kgTime second sTemperature kelvin K
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Some Standard Units in the Metric System
Quantity Measured
Name of Unit Abbreviation
Mass gram g
Length meter m
Volume liter L
Time seconds s
Temperature Kelvin K
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King Henry Died By Drinking Chocolate Milk
K H D B d c m
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Tro's "Introductory Chemistry", Chapter 2 23
Common Prefixes in the SI System
Prefix SymbolDecimal
EquivalentPower of 10
mega- M 1,000,000 Base x 106
kilo- k 1,000 Base x 103
deci- d 0.1 Base x 10-1
centi- c 0.01 Base x 10-2
milli- m 0.001 Base x 10-3
micro- m or mc 0.000 001 Base x 10-6
nano- n 0.000 000 001 Base x 10-9
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Let’s Try A Few
125 cm = ____________ mm
0.2568 L = _________ mL
2.56 kg = ________ g
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Factor LabelDimensional Analysis EASY way to convert from one unit to
another unit!!
WE will be doing this ALL YEAR long! So you better pay attention now!
UNITS ARE EXTREMELY IMPORTANT
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Units Always write every number with its
associated unit. Always include units in your calculations.
You can do the same kind of operations on units as you can with numbers.○ cm × cm = cm2
○ cm + cm = cm○ cm ÷ cm = 1
Using units as a guide to problem solving is called dimensional analysis.
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Problem Solving and Dimensional Analysis
Many problems in chemistry involve using relationships to convert one unit of measurement to another.
Conversion factors are relationships between two units.May be exact or measured.
Conversion factors generated from equivalence statements.e.g., 1 inch = 2.54 cm can give or in1
cm54.2cm54.2
in1
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Problem Solving and Dimensional Analysis, Continued
Arrange conversion factors so the starting unit cancels.Arrange conversion factor so the starting unit is on
the bottom of the conversion factor. May string conversion factors.
So we do not need to know every relationship, as long as we can find something else the starting and desired units are related to :
unit desired unit related
unit desired
unitstart
unit relatedunitstart
unit desired unitstart
unit desiredunitstart
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Systematic Approach
1. Write down the given amount and unit.
2. Write down what you want to find and unit.
3. Write down needed conversion factors or equations.
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Common Units and Their EquivalentsLength
1 kilometer (km) = 0.6214 mile (mi)1 meter (m) = 39.37 inches (in.)1 meter (m) = 1.094 yards (yd)
1 foot (ft) = 30.48 centimeters (cm)1 inch (in.) = 2.54 centimeters (cm) exactly
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Common Units and Their Equivalents, Continued
Volume1 liter (L) = 1000 milliliters (mL)1 liter (L) = 1000 cubic centimeters (cm3)1 liter (L) = 1.057 quarts (qt)
1 U.S. gallon (gal) = 3.785 liters (L)
Mass1 kilogram (km) = 2.205 pounds (lb)
1 pound (lb) = 453.59 grams (g)1 ounce (oz) = 28.35 (g)
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Lets take a look at one!
I drive 20 miles to school every day. I want to know how many kilometers I drive.
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Lets Try a Few
125 lb = ________ kg
2.5 gallons = ________ L
3.1 km = _________ miles
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Significant Figures and Factor label
Day Four
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Exact Numbers vs. Measurements
Sometimes you can determine an exact value for a quality of an object.Often by counting.
○ Pennies in a pile.
Sometimes by definition○ 1 ounce is exactly 1/16th of 1 pound.
Whenever you use an instrument to compare a quality of an object to a standard, there is uncertainty in the comparison.
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Reporting Measurements Measurements are written to indicate the
uncertainty in the measurement. The system of writing measurements we
use is called significant figures. When writing measurements, all the digits
written are known with certainty except the last one, which is an estimate.
45.872
CertainEstimated
45.872
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Skillbuilder 2.3—Reporting the Right Number of Digits
A thermometer used to measure the temperature of a backyard hot tub is shown to the right. What is the temperature reading to the correct number of digits?
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Reporting Numbers with Sig. Figs When we report numbers in this class
we need to make sure that we do not report them more specific than they really are. WHAT???
Volume of a box
Length = 7.12 cm
Width = 2.15 cm
Height = 2.15 cm
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How do I know if a number is significant?
1. All NONZERO digits are significant
2. Zeros between two nonzero numbers are significant
3. Trailing zeros are significant
4. Leading zeros are NOT significant, they are only place holders
5. Zeros at the end of a number but before a decimal are NOT significant
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Lets try a few
0.0035 1.080 2371 2.97 x 105
100000 0.500 58.31
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Factor Label (Multi-step)
I went to the Yukon last summer and the speed limit sign said 105 km/hr. What was the speed limit in mi/hr?
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If I drive a total of 50 miles a day and my car gets 49 miles/gallon. How much does it cost me a week to drive to work? Assuming price for gas is $2.50/gallon.
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A circle has an area of 2,659 cm2. what is its area in square meters?
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Significant Figures and Factor Label
Day Five
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Significant Figures in CalculationsADDITION AND SUBTRACTION
The difference and sum carries the same number of decimal places as the quantity carrying the FEWEST decimal places.
3.449 cm – 0.76 cm =
2.5 cm + 2 cm =
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Significant Figures in Calculations(MULTIPLICATION AND DIVISION)
The results carries the same number of significant figures as the factor with the FEWEST figures.
5.892 cm X 6.10 cm =
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Lets take a look back at our Volume of a Box!!
Volume of a box
Length = 7.12 cm
Width = 2.15 cm
Height = 2.15 cm
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Lets Try a Few!
1.01mm x 0.12 cm x 53.51 cm =
56.55 cm x 0.920 cm =
345.0 ml / 120 ml =
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Significant Figures Lab
Day Six
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Mastering Chemistry Website
Day Seven
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Density Day Eight
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Density
Ratio of its mass to volume
“How much stuff is in a given space”
Differs from one substance to another
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How do I calculate DENSITY?
What about the units?
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I have a sample of platinum that has a mass of 5.84g and it displaces 0.556 cm3 of water. What is the density?
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Lets Try a Few!
The gasoline in an automobile gas tank has a mass of 60.0 kg and a density of 0.752g /cm3. What is its volume in ml?
A steel cylinder has a volume of 246 cm3 and a density of 7.93 g/cm3. What is its mass in kg?
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Density Day 2 Day Nine
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Measurement and Density Lab
(Sig. Figs. Lab)
Day Ten and Eleven
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Practice TestDay Twelve
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reviewDay Thirteen
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Test
Day Fourteen