Today…
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Turn in:
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Nothing
Our Plan:
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Daily Challenge
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Scientific Notation, Accuracy, Precision, Error Notes
Worksheet #1
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Wrap Up – Rally Robin
Homework (Write in Planner):
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Complete WS #1 by next class

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The number
602200000000000000000000 is used so frequently in chemistry that it has its own name;
Avogadro’s number. What would be a better way of writing it?

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To write a number in scientific notation:
1.
2.
3.
Move the decimal so that the number is between 1 and 10.
The exponent is the number of tens places you moved the decimal
Moving the decimal right = - exponent
Moving the decimal left = + exponent

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65000 m =
6.5 x 10 4 m
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0.0000156 s =
1.56 x 10 -5 s
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0.24 m/s =
2.4 x 10 -1 m/s
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6.7 mm =
6.7 x 10 0 mm

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Change it from scientific notation to a standard number by moving the decimal.
Example
1.4 x 10 6 = 1,400,000
2.6 x 10 -4 = 0.00026

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Change the numbers to the same exponent.
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Add or subtract the numbers
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Example: 4.1 x 10 6 + 8.5 x 10 7
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0.41 x 10 7 + 8.5 x 10 7 = 8.91 x 10 7

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Multiply the numbers
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Add the exponents
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Example: (4 x 10 6 )(2 x 10 8 )
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8 x 10 14

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Divide the numbers
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Subtract the exponents
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Example: (9 x 10 7 )/(3 x 10 4 )
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3 x 10 3

1.
2.
3.
4
5
8
6
6
3

1.
2.
3.
5.45 x 10 5
1.995 x 10 15
1.53 x 10 3

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Use your scientific calculator.
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The EE button means x10 ^
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Do the Try it Out problems again using your calculator and see if you get the correct answers!

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Accuracy – compare to the
CORRECT value
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Precision – compare to the values of two or more
REPEATED MEASUREMENTS

Accurate, Precise, Both, Neither?
Accurate

Accurate, Precise, Both, Neither?
Precise

Accurate, Precise, Both, Neither?
Neither

Accurate, Precise, Both, Neither?
Precise

Accurate, Precise, Both, Neither?
Both

Accurate, Precise, Both, Neither?
Accurate

Percent Error = |experimental - actual| actual value
X 100
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The absolute value is present so that percent error is always POSITIVE!

Example
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Working in the laboratory, a student finds the density of a piece of pure aluminum to be 2.85 g/cm 3 . The accepted value for the density of aluminum is 2.699 g/cm 3 . What is the student's percent error?
Percent Error = |2.85 – 2.699|
2.699
X 100 =
5.59%

Try It Out
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A student takes an object with an accepted mass of 200.00 grams and masses it on his own balance. He records the mass of the object as
196.5 g. What is his percent error?
Percent Error = |196.5 – 200.00|
200.00
1.75%
X 100 =

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Complete Worksheet #1 by next class
Worksheets are…
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A completion grade (i.e. You do not get a grade until it is 100% finished)
10 points on time
-2.5 points each day it’s late

Wrap Up
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Rally Robin
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Pair up with your shoulder partner.
Divide a deck of cards in half. Take turns asking each other the questions on the cards.
Be sure to cover the answer with your finger.

Today…
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Turn in:
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Get out WS#1 to Check
Our Plan:
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Scientific Notation Clicker Review
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Scientific Notation Quiz
Notes – Significant Figures/Units of Measurement
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WS #2
Bluff
Homework (Write in Planner):
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Complete WS #2 by next class (9/12)
QUIZ OVER SIG FIGS NEXT TIME!

Units in Chemistry
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When you add or subtract two numbers, they must have the same units.
The answer then has those units as well.
Example: 4 m + 12 m = 16 m
When you multiply, you also multiply the units.
Examples:
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4 m x 5 m = 20 m 2
2 g x 3 s = 6g·s
When you divide, you also divide the units.
Examples:
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4 m / 2 s = 2 m/s
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8 g / 2 mL = 4g/mL

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***All nonzero numbers are significant***
125, 689 has 6 significant figures (sig figs)
156 has 3 sig figs
1.
Zeros between nonzero numbers are significant.

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2.
Zeros in front of nonzero numbers are not significant

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3.
Zeros at the end of a number and to the right of a decimal are significant

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4.
Zeros at the end of a number are NOT significant. If there is a decimal at the end, they
ARE.

Decimal
Start at the first nonzero number on the left and count every number right
No
Decimal
Start at the first nonzero number on the right and count every number left

Unlimited Significant Figures
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Counting – There are 23 students in the classroom
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Could also be expressed as 23.0 or
23.00000000000000 etc.
Conversion Factors – 60 min = 1 hour
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Exact quantities do not affect the process of rounding

4.
5.
6.
2.
3.
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1.
How many sig figs?
0.00125
3
1.12598000
3,000 1
0.0100103
6
9
5,500.
4
1.23 x 10 5 3

2.
3.
4.
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1.
Round the following numbers so that they have 3 significant figures:
1.36579 = 1.37
120 = 1.20 x 10 2 OR 120.
145,256,987 = 145,000,000
0.0001489651 = 0.000149

To Multiply & Divide
Sig Figs…
1.
2.
Count the number of sig figs in each number
Round the answer so that it has the same number of sig figs as the number in the problem with the fewest.

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16.19 g / 4.2 mL
= 3.8547619 g/mL
16.19 has 4 sig figs
4.2 has 2 sig figs, so the answer should have 2 sig figs
3.9 g/mL

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9.3 m x 0.00167 m
= 0.015531m
2
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9.3 m has 2 sig figs, 0.00167 has 3 sig figs
Therefore, the answer must have only 2 sig figs.
0.016 m 2

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0.014
0.1
(1.23 x 10 6 )(3.5 x 10 4 ) = 4.3 x 10 10
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6.988 x 10 -4

Stop
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1A. How many sig figs are in 0.001023?
1B. Solve 456 x 3.2
2A. How many sig figs would the answer have if you calculated 2.1 x 0.01?
2B. How many sig figs are in 123,000?
3A. Solve 2.7 x 3
3B. How many sig figs would the answer have if you calculated 1.4/3.789?

4A. What is 235,489 rounded to 2 sig figs?
4B. Solve 1/236
5A. Solve 3.7914/9.2
5B. What is 1,926,560 rounded to 1 sig fig?
6A. How could you write 230 with 3 sig figs?
6B. What is 0.00056798 rounded to 4 sig figs?

Today…
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Turn in:
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Get out WS#2 to Check
Our Plan:
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Sig Fig Race
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Sig Fig Quiz
Notes – Significant Figures in Measurement
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Practical Lab - Measurement
Wrap Up – Measure Up
Homework (Write in Planner):
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Fill out p. 9 – top of 11 using your text by next class!

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When doing any measurements in chemistry, it is important that you use the correct precision.
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All measurements should be made by writing all units you know and estimating the last unit.

10
10
20
30
20
30
40
50
40
50
60
60
70
54
38
70
13.9
2 4 6 8 10 12 14

2 4 6
3.4
1.16
0.5
1 1.5
72
20 40 60

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5.3
2 4 5 6
1.58
0.5
1 1.5
43
20 40 60

Today
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Before Class:
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Get out Note Booklet, Calculator, & Pencil
Our Plan:
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Mix/Group Review (#1-11)
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Challenge
Notes - Conversions
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WS #3
Wrap Up – Practice Problem from the Worksheet
Homework (Write in Planner):
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Try out some of the problems on the worksheet

Review Time
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Open up your notebooklet to p. 11.
Answer questions 1 – 6.
Get up and move around the classroom.
When the instructor says “group by the answer to #___” you have to form a group of students that is the same as the answer to the problem!

Review Time
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Now answer questions 7 – 11 on your own.
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When you are finished pair up with your face partner and share your answers.

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How many sig figs:
1.
2.
102.32500
560.
3.
0.0012501
What is the exponent?:
4.
5.
6.
420=
36,000,000
60 =

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Round these numbers so that they have 3 sig figs:
7.
8.
103,250
567.9
103,000 or 1.03 x 10
568 or 5.68 x 10 2
5
9.
10.
11.
0.0012561
0.00126 or 1.26 x 10 -3
100 100. or 1.00 x 10 2
Read the measurement below correctly.
43
20 40 60

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How old are you, in minutes?

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Definition: a ratio of equivalent units
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It is always equal to 1
When multiplying by a conversion factor, the numerical value is changed, but the actual size of the quantity remains the same

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When working with conversion factors, we use the Factor-Label
Method (dimensional analysis)
The factor is the number that explains the relationship between two things
The labels are its’ units

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4 quarters = 1
1 dollar
OR
Factor
1 dollar = 1
4 quarters
Label

12 months = 1
1 year
1 foot = 1
12 inches

Rules for using Conversion
Factors
1.
2.
3.
Always start by writing what you know from the problem.
Multiply by a conversion factor so that the units cancel out (same unit in numerator and denominator)
Continue converting until your answer is in the desired units .

Example 1 – your age in minutes
Checklist:
 I started by writing what I knew
 All units cancel
 My answer is in minutes

Mrs. C’s top 4 reasons for NOT using the Factor-Label Method
1.
2.
You’re super-intelligent and enjoy solving relatively simple problems in the most complex manner.
You're tired of always getting the correct answers.

Mrs. C’s top 4 reasons for NOT using the Factor-Label Method
3.
You’re artistic, and rather than using Mrs. C’s concretesequential method of solving problems you want to use your own random method such that you create abstract patterns and designs on paper that you might be able to sell as artwork.

Mrs. C’s top 4 reasons for NOT using the Factor-Label Method
4.
Let's say that you have no interest in going to the prom or making the soccer team, and you don't mind being unpopular, unattractive, ignorant, insecure, uninformed, and unpleasant.
Otherwise,
You Need the Factor-Label Method!

Testimonials
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"I was a South High School student who dozed off while Mrs. C taught us the Factor-Label method in chemistry. I never quite got the hang of it. It irritated me... all of those fractions. I never really liked fractions. Although my grades had been pretty high, I got a D in chemistry and subsequently did not take any more high school science classes. It was not long before I started on drugs, and then used crime to support my drug habit. I have recently learned the factor-label method and realize how simply it could have solved all of my problems. Alas, it is too late. I won't get out of prison until 2022 and even then, my self image is permanently damaged. I attribute all of my problems to my unwillingness to learn the factorlabel method ." -Jane

Testimonials
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"I thought I knew everything and that sports was the only thing that mattered in high school. When Mrs. C taught our class the factor-label method, I didn't care about it at all. I was making plans for the weekend with my girlfriend who loved me because I was a running back and not because of chemistry. While other kids were home solving conversion problems, I was practicing making end sweeps. Then one day I was hit hard. Splat. My knee was gone. I was a total loser. My girl friend deserted me. My parents, who used to brag about my football stats, stopped loving me and started getting on my case about grades. I decided to throw myself into my school work. But I couldn't understand anything. I would get wrong answers all of the time. I now realize that my failure in school came from never having learned the factor-label method . I thought everyone else was smarter than me. After the constant humiliation of failing I finally gave up. I am worthless. I have no friends, no skills, no interests. I have now learned
is too late." -Bill the factor-label method , but it

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How many dollars do you have if you have 38 quarters?
9.5 dollars

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How many nanoseconds are in one week?
600,000,000,000,000 nanoseconds

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How many milligrams are in 12 g?
12,000 mg

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Now try the next three problems in your notes on your own.
Checklist:
 I started by writing what I knew
 All units cancel
 My answer is in desired units

1.
2.
3.
790,000,000 seconds
6.71 x 10 3 grams
5.3 x 10 3 mL

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Today…
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Turn in:
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Get WS #3 out
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On Mrs. C’s birthday she will be 1.041 x 10 9 seconds old. How many years old will she be?
Our Plan:
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Pass the Paper
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Work on Worksheet #3
Notes - Density
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WS #4
Wrap Up – Density Problem
Homework (Write in Planner):
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Complete WS #3 &#4 by next class
QUIZ OVER BOTH WORKSHEETS NEXT TIME!

Review
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Pass the Problem
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Each student has a problem to solve. The first student will do step 1 (write what you know) and pass the paper to the next student who will complete the second step.
Continue passing the paper until you get the answer.
Example: How many days are in 60 seconds?

Pass the Paper Answers
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Density = Mass/Volume
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Volume of liquids is measured in liters or milliliters
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Volume of solids is length x width x height

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A bar of silver has a mass of 68.0 g and a volume of 6.48 cm 3 .
What is the density of silver?
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10.5 g/cm 3

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A copper penny has a mass of 3.1 g and the density of copper is
8.8571 g/cm 3 . What is the volume of the penny?

0.35 cm 3

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What is the mass of a pure silver coin that has a volume of 1.3 cm 3 ? The density of silver is 10.5 g/cm 3 .

14 g

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Wrap Up - Density Review (p. 15 Notes)
• Four graduated cylinders each contain a different liquid: A, B, C, and D.
• Liquid A: mass = 18.5 g; volume = 15.0 mL
• Liquid B: mass = 16.5 g; volume = 8.0 mL
• Liquid C: mass = 12.8 g; volume = 10.0 mL
• Liquid D: mass = 20.5 g; volume = 12.0 mL
• Examine the information given for each liquid, calculate the density, and predict the layering of the liquids if they were carefully poured into a larger graduated cylinder.

A – 1.23 g/mL
Density = Mass/Volume
C – 1.28 g/mL
D – 1.71 g/mL
B – 2.1 g/mL

Today…
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Turn in:

Get WS #3 & #4 out to be graded
Our Plan:
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Which Word Am I?
Conversions/Density Quiz
Lab
Wrap Up – High Five
Homework (Write in Planner):
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Missing Work

Review – Which Word Am I
(p. 15 Notes)
1.
2.
4.
5.
6.
3.
Mass divided by volume
The numbers that are known in a measurement plus one estimated digit
How close your measurements are to the true value
How close your measurements are to each other
Convert 3.69 meters into inches.
What is the volume of a cube that has a mass of
7.9 g and a density of 9.45 g/cm 3 ?

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Today…
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
Turn in:

Get Lab Packet Out, Calculator, Pencil
Our Plan:
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LAB – DUE TODAY
Work Day
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Missing Work
Test Review
Homework (Write in Planner):
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
Test Review due next class
TEST NEXT TIME!

Today…
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
Turn in:

Get out Test Review to check

Turn in Measurement Lab if you haven’t yet!
Our Plan:

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
Worksheet Race
Go over Test Review, then turn it in
Unit 3 Test

Periodic Table Basics Activity
Homework (Write in Planner):

PT BASICS DUE NEXT MONDAY!

After the Test

PT BASICS HELP