Transcript Unit 2 - USD305.com

As You Come In
Get out your unit 1 goal sheet,
fill it out and turn it in.
 Grab Unit 2 notes booklet and
the worksheet packet.
 Review symbols cards with your
shoulder partner

9/3 & 9/4


What:
 You will determine the difference between
accuracy & precision; convert using scientific
notation & calculate % error
How:







Review chemical symbols
Take symbols quiz
Notes
WS #1
Chemical symbols Bingo!
Homework:
Complete WS #1 – worksheets are completion points
only!
Element Song
http://www.youtube.com/watch?v=GFIvXVMbII0
If they can learn the elements,
why can’t you?


http://www.youtube.com/watch?v=GcT
qTgBaMQM
http://www.youtube.com/watch?v=nUc
y9eb8cYU
Unit 2
Chapter 3
Scientific Measurement
Daily Challenge

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?
Scientific Notation

1.
2.
3.
To write a number in
scientific notation:
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
Examples
65000 m = 6.5 x 104 m
 0.0000156 s = 1.56 x 10-5 s
-1
 0.24 m/s = 2.4 x 10 m/s
 6.7 mm = 6.7 x 100 mm

To Write a number in
Standard Form
Change it from scientific notation
to a standard number by moving
the decimal. The exponent
becomes the number of spaces
you moved the decimal.
 Example
1.4 x 106 = 1,400,000
2.6 x 10-4 = 0.00026

Adding & Subtracting
1. Change the numbers to the same
exponent.
2. Add or subtract the numbers
Example: 4.1 x 106 + 8.5 x 107
 0.41 x 107 + 8.5 x 107 = 8.91 x 107

Multiplication
Multiply the numbers
 Add the exponents

Example: (4 x 106)(2 x 108)
 8 x 1014

Division
Divide the numbers
 Subtract the exponents

Example: (9 x 107)/(3 x 104)
 3 x 103

Try It Out!
1.
2.
3.
4
10
5
10
3.5 x
+ 5.1 x
(5.7 x 108)(3.5 x 106)
6
3
(6.9 x 10 )/(4.5 x 10 )
Answers
1.
2.
3.
5
10
5.45 x
15
1.995 x 10
3
1.53 x 10
Or…
Use your scientific calculator.
 The EE button means x10^
 Do the Try it Out problems
again using your calculator and
see if you get the correct
answers!

Accuracy & Precision
Accuracy – compare to the
CORRECT value
 Ex: You should have gotten
1 gram of each material in
the separation of mixtures
lab

Accuracy & Precision
Precision – compare to the
values of two or more
REPEATED MEASUREMENTS
 Ex: Multiple trials

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
Percent Error = |experimental - actual|
X 100
actual value

The absolute value is present so that percent
error is always POSITIVE!
Example

Working in the laboratory, a student finds the
density of a piece of pure aluminum to be 2.85
g/cm3. The accepted value for the density of
aluminum is 2.699 g/cm3. What is the student's
percent error?
Percent Error = |2.85 – 2.699|
X 100 =
2.699
5.59%
Try It Out

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|
X 100 =
200.00
1.75%
STOP!


Complete Worksheet #1 by next
class
Worksheets are…
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

As You Come In
Get out WS #1 to be
checked
 Get out U2 notes booklet
 Questions from Worksheet?

Agenda for 9/5 & 9/6

What:

You will identify and round significant
figures

How:

Symbols review
 Symbols quiz #2
 Scientific notation quiz
 Notes: Sig Figs and Measurement
 Worksheet #2
Homework: Complete WS #2

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:




4 m x 5 m = 20 m2
2 g x 3 s = 6g·s
When you divide, you also divide the units.
Examples:


4 m / 2 s = 2 m/s
8 g / 2 mL = 4g/mL
Think about it!

What does the word
“significant” mean?
Significant Figures

The numbers that are
known, plus a digit that
is estimated
RULES
***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.

3
40.7 mL has ______
sig figs

6 sig figs
870,009 g has _____
RULES
2.
Zeros in front of nonzero
numbers are not
significant

2 sig figs
0.00011 s has _____

3 sig figs
0.956 g/mL has _____
RULES

Zeros at the end of a number
and to the right of a decimal
are significant
6 sig figs
85.0000 kg has _____

9 sig figs
2.00000000 L has _____
3.
RULES
4.
Zeros at the end of a number
are NOT significant. If there
is a decimal at the end, they
ARE.

4 sig figs
2000. m/s has _____

1 sig figs
2000 m/s has _____
EASY RULE!
Decimal Start at the first nonzero
number on the left and
count every number right
No
Start at the first nonzero
Decimal number on the right and
count every number left
Look at these numbers again
2000. m/s has _____ sig figs
2000 m/s has _____ sig figs
Unlimited Significant Figures

Counting – There are 23 students in the
classroom


Could also be expressed as 23.0 or
23.00000000000000 etc.
Conversion Factors – 60 min = 1 hour

Exact quantities do not affect the process of
rounding
Try It Out

1.
2.
3.
4.
5.
6.
How many sig figs?
0.00125 3
1.12598000 9
3,000 1
0.0100103 6
5,500. 4
1.23 x 105 3
Rounding

1.
2.
3.
4.
Round the following numbers so
that they have 3 significant figures:
1.36579 = 1.37
120 = 1.20 x 102 OR 120.
145,256,987 = 145,000,000
0.0001489651 = 0.000149
Stop Here!

You have 10 minutes to
work on the front side of
WS #2
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.
Example 1



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
Example 2



9.3 m x 0.00167 m
= 0.015531m2
9.3 m has 2 sig figs, 0.00167 has 3 sig figs
Therefore, the answer must have only 2
sig figs.
0.016 m2
Try It Out!
(1.23)(0.011) = 0.014
 12.63000/100 = 0.1


(1.23 x 106)(3.5 x 104) = 4.3 x 1010

0.0045912/6.570 =
6.988 x 10-4
Stop

Complete Worksheet #2
Bluff
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?
Bluff
4A.
4B.
5A.
5B.
6A.
6B.
What is 235,489 rounded to 2 sig figs?
Solve 1/236
Solve 3.7914/9.2
What is 1,926,560 rounded to 1 sig fig?
How could you write 230 with 3 sig figs?
What is 0.00056798 rounded to 4 sig figs?
As You Come In

Get out WS #2 and
have checked for points
Agenda 9/9



What:
 You will apply using sig figs in measurement
to a practical lab
How:
 Sig Figs Race
 Sig Figs Quiz
 Notes- sig figs in measurement
 Practical Lab
Homework: Complete pages 10 & 11 in notes
from your book
Sig Figs in
Measurements
When doing any measurements in
chemistry, it is important that you
use the correct precision.
 All measurements should be
made by writing all units you
know and estimating the last unit.

Examples
10
20
30
40
54
50
70
60
38
10
30
20
50
40
70
60
13.9
2
4
6
8
10
12
14
More Examples!
2
4
6
0.5
1
1.5
20
40
60
3.4
1.16
72
Units of Measurement
Every measurement in
chemistry MUST HAVE A
UNIT!
 Without a unit, the number
means nothing!
 We will use SI units in class

Wrap Up – Clicker!
2
4
5
6
0.5
1
1.5
20
40
60
5.3
1.58
43
As You Come In
Get out your Unit 2 notes,
calculator and pencil.
 Music today will play during
review time

Agenda 9/10 & 9/11

What:


How:



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You will calculate conversion problems.
Mix/Group Review
Conversions Notes
Work on WS #3
Homework:

Try some of the problems on WS #3
Review Time


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!
Mix/Group


How many sig figs:
1. 102.32500
2. 560.
3. 0.0012501
What is the exponent?:
4. 420=
5. 36,000,000
6. 60 =
Review Time
Now answer questions 7 – 11
on your own.
 When you are finished, pair up
with your face partner and
share your answers.

Think-Pair-Share

Round these numbers so that they have 3 sig figs:
7.
8.
9.
10.
11.
103,250 103,000 or 1.03 x 105
567.9 568 or 5.68 x 102
0.0012561 0.00126 or 1.26 x 10-3
100
100. or 1.00 x 102
Read the measurement below correctly.
20
40
60
43
Challenge
Would you be breaking the
speed limit in a 40 mi/h zone
if you were traveling at 60
km/h?
 http://www.youtube.com/wat
ch?v=Qhm7-LEBznk

Challenge

How tall are you in
Cheetos?
Cheetos conversion
Conversion Factors
Definition: a ratio of equivalent
units
 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

Conversion Factors
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

Examples

4 quarters = 1 OR
1 dollar
Factor
1 dollar = 1
4 quarters
Label
Examples
12 months = 1
1 year
1 foot
12 inches
=1
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
Example 2

How many dollars do you have if you
have 38 quarters?
9.5 dollars
Example 3

How many nanoseconds are in one week?
600,000,000,000,000
nanoseconds
Example 4

How many milligrams are in 12 g?
12,000 mg
TRY IT OUT!

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
The Answers…
1.
2.
3.
790,000,000 seconds
3
6.71 x 10 grams
3
5.3 x 10 mL
Still don’t get it?

Watch this factor-label method video!
STOP!



Start Worksheet #3.
You must show work and you must
use the factor-label method!
Remember worksheets are
completion grades- no credit until
done completely!
As You Come In


Get out WS #3 and notes
Calculate the following problem on the
back of your notes:

On my last birthday Mrs. Hammond turned
1.23 x 109 seconds old. How many years old
am I?
Agenda 9/12 & 9/13



What:
 You will calculate density problems.
How:
 Pass the problem review
 Notes-Density
 WS #4
 Begin Density Lab
Homework: Complete WS 4
Review

Pass the Problem


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?
Conversion Problem Answers
569
96,400
8
1,000,000

Density Review
Density = Mass/Volume
 Volume of liquids is measured
in liters or milliliters
 Volume of solids is length x
width x height

Example


A bar of silver has a mass of 68.0
g and a volume of 6.48 cm3.
What is the density of silver?
10.5 g/cm3
Example


A copper penny has a mass of 3.1
g and the density of copper is
8.8571 g/cm3. What is the
volume of the penny?
0.35 cm3
Try It Out


What is the mass of a pure silver
coin that has a volume of 1.3
cm3? The density of silver is 10.5
g/cm3.
14 g
Using Density as a
Conversions Factor


What volume of ethanol (in liters)
would you have if you acquire 126.56g
of ethanol? The density of ethanol is
0.789 g/cm3.
0.16032 L
Try It Out in your notes!


The density of apples is 0.641 g/cm3. If
an apple has a mas of 0.089 kg, what is
its volume?
140 cm3
STOP!
You have 10
min. to work on
WS #4

As You Come In
Get out WS #4 to be checked
 Complete the Wrap Up on Density
on page 15 of your notes.
 Then list the letters in order of how
they would layer out if this were put
into a graduated cylinder.

Density Review
A – 1.23 g/mL
C – 1.28 g/mL
D – 1.71 g/mL
B – 2.1 g/mL
Density = Mass/Volume
Agenda 9/16

What:


How:



You will apply correct measurement
techniques and calculate density.
Conversions & Density Quiz
Measurement & Density Lab
Homework: Missing Assignments
Wrap Up

What questions do you
have on the lab?
As You Come In
Get out your Measurement &
Density Lab, a pencil and
your calculator and your U2
notes
 Pick up the U2 Test Review

Agenda 9/17 & 9/18

What:


You will solve density & conversion
problems
How:


Which word am I? Review
Complete Measurement & Density Lab
Homework: U3 Test Review
*U3 Test next block
*All missing assignments for when you
take your test!

Review – Which Word Am I
(p. 15 Notes)
1.
2.
3.
4.
5.
6.
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/cm3?
Answers






1.
2.
3.
4.
5.
6.
Density
Significant Figures
Accuracy
Precision
145 inches
.84 cm3
As You Come In
Get out your Unit 2 Test
Review to be checked
 Turn in your Measurement
Lab if you haven’t yet!

Agenda 9/19 & 9/20

WHAT:


How:



You will be assessed on Unit 2 material
WS Race
Take Unit 2 Test
Homework:

PT Basics Activity (Poster)
After the Test

PT BASICS HELP