Welcome to Chemistry!
with Mrs. Strain Rm. 403
 Do Now:.Find your seat & distribute papers on desk.
 HWK for all classes:
1.
Read “Welcome to Chem A” page on my website to understand
2.
3.
4.
procedures for this class. Complete hand out and return on
Tuesday, 9/8/14
Start “Intro to WebAssign”: due Monday
Supplies & Signature Sheet due ASAP but no later than Tuesday,
9/8/14
Check board for other HW assignments based on class period
 Safety Quiz – on lab day AFTER completing safety lab. Review safety
contract info
 Math Assessment on first non-lab day starting Monday(no need to
study )
What is Chemistry?
 Your Task: on a piece of paper answer this question...
What is Chemistry?
 Does your answer sound like any of these responses?
What is Chemistry?
 The definition we’ll work off of this year:
Chemistry is the study of matter & of
the changes it undergoes
 Composition
 Structure
 Properties
 Energy changes
A Quick Demo
 If we want to describe matter & its changes, there is
a certain language we need to become familiar
using.
 There are good observations & there are bad
observations.
 During the demo: Write down what you see
happening. Imagine you were trying to explain
this to someone who is not present in the room.
Two Types of Measurements
 In science we can take two different kinds of
observations:
 Qualitative
 Quantitative
 Qualitative (think “quality”):
observations using words
 Quantitative (think “quantity”):
observations using numbers and units.
Here’s what I am hoping to see…
 Qualitative observations:
 States of matter
 Color
 Texture
 Smell
 Viscosity
 Quantitative observations:
 Amount of substances present
 Step by step procedure!
Here’s what I don’t want to see…
 Opinionated language
 “I feel”
 “I like”
 Non-specific wording
 “sort of…”, “lots of…”, ”kinda”
 Descriptions that sound like a kindergartener wrote
them
 “It was all bouncy and …”
 describing something as “chunky”
Taking Measurements in
Chemistry
Ch. 2 The SI or Metric System
The SI System
 Around 1793, scientists all over the
world began to agree upon a single
measurement system called
 Le Systeme International d’
Unites or SI System
 7 base units
 The idea was to create a unifying
system of weights and
measurements
Quantity
Unit
Symbol
Length
Mass
Time
Temperature
Amount of a
substance
Electric
current
Luminous
intensity
Meter
Kilogram
Second
Kelvin
Mole
m
kg
s
K
mol
Ampere
A
Candela
cd
• Crash Course: Units
• Where’s volume??
Derived Units
 Combinations of base units
 Volume: amount of space taken up by an object
 Derived SI unit is cubic meter, m3
 More often we use cm3 = mL
D=m
V
 Density: ratio of mass to volume
 g/cm3 of g/mL or g/L
 Does not change for a given substance
m
D
V
Other Derived Units
Quantity
Area
Molar Mass
Energy
Unit
Symbol
Derivation
square meter
grams per
mole
joule
m2
g/mol
Length x width
Mass / amount
J
Force x length
Larger quantities
Metric
Prefix
Symbol
Meaning
Scientific
Notation
mega
M
Million / 1,000,000
1 x 106
kilo
k
Thousand / 1,000
1 x 103
hecta
h
Hundred / 100
1 x 102
deka
da
Ten / 10
1 x 101
Base Unit
deci
d
Tenth / .1
1 x 10-1
centi
c
Hundredth / .01
1 x 10-2
milli
m
Thousandth / .001
1 x 10-3
Millionth / .000 001
1 x 10-6
micro
nano
n
Billionth / .000 000 001
1 x 10-9
pico
p
Trillionth / .000 000 000 001
1 x 10-12
Using SI prefixes: Number Line Method
Conversions from one SI prefix to another (within 1 of the 7 base
units) can easily be preformed by moving the decimal place of a
quantity by 1 space or 3, left or right.
Practice Problems
1.
5.6 cm to m
2. 56 mg to g
3.
340 mm to cm
4. 1.2 ML to L
0.056 m
0.056 g
34 cm
1,200,000 L
Using SI prefixes: Factor-Label Method
(Dimensional Analysis)
 Method requires translating two equal quantities into a
ratio or conversion factor
 Ex: 16 oz = 1 lb can be written 16 oz
or
1 lb
1 lb
16 oz
 Notice: a conversion factor can be represented 2 ways!
 This can be done with any 2 equal quantities
 2 grand slams = 8 R.B.I.’s
 1 fortnight = 14 days
 100 cm = 1 m
Using SI prefixes: Factor Label Method
 Using the factor label method to solve problems
 Ex: How many dimes are in 14 dollars?
Write the given
2. Write conversion factor
3. Solve, crossing out units that have divided out
1.
14 dollars x
10 dimes
1 dollar
=
14o dimes
Using Factor-Label Method
 Sample Problems:
Converting 9.8 g to kg
9.8 g x 1 kg
= 0.0098 kg
1000. g
Converting 9.8 kg to g
9.8 kg x 1000. g
1 kg
= 9800 g
“1” goes in
front of larger
unit!
Practice Problems
 Try these practice problems, but now using the Factor-
Label Method
 (I realize this seems like more work than the number
line method…but there’s a reason why we have to
learn this)
0.056 m
1.
5.6 cm to m
2.
1.2 L to ML
1.2 x 10-6 ML
3.
100 mm to cm
4.
25 kg of water to mL
10 cm
2500 mL
Do Now: Test your Metric System “With-it-ness”
 For each of the measurements on your worksheet,
decide the appropriate quantity that should be
assigned to it.
Density Practice
 Density Formula
D=m
V
 Use Density Pyramid as a short cut
m
D
V
Taking Measurements in
Chemistry
Accuracy vs. Precision
Accuracy & Precision in Measurements
 Accuracy: closeness of measurements to correct
value
 Precision: closeness of a set of measurements to
each other (assuming they’re made in the same
way)
High accuracy
High precision
Low accuracy
High precision
Low accuracy
Low precision
Accuracy vs. Precision
 Example: A student measures the density of a
sample of nickel.
Density Result (g.mL -1)
Trial 1
7.8
Trial 2
7.7
Trial 3
7.8
 The density of nickel is 8.9 g.mL -1
 So the results were: Precise, but not accurate
Accuracy & Precision (continued)
 Some error always exists in measurements
 Skill of measurer
 Conditions of measurements
 Limitation of instruments
Percentage Error
 Accuracy of an individual value (or average) can be
compared to the correct/accepted value
% Error = Experimental – Accepted x 100
Accepted
Percentage Error
 What is the percentage error for a mass measurement
of 17.7 g, given that the correct value is 21.2 g?
 A volume is measured experimentally as 4.26 mL.
What is the percentage error, given that the accepted
value is 4.15 mL?
Taking Measurements in
Chemistry
Significant Figures
Exploring Uncertainty and Precision
The Paper Clip Activity
 Measuring always involves some degree of
estimation (i.e. uncertainty)
Significant Figures
 Certain digits: digits that represent a marking on a
scale or non-blinking number of a display
 Uncertain (estimated) digits: digits that represents
the space between the marks on a scale or the blinking
number on a display
 Sig Figs – all digits of certainty + 1 estimated
Sig Figs: Using the Pacific/Atlantic Rule
 Step 1: Ask yourself: is the decimal point present or absent?
 Step 2: Determine which way to start counting
P resent
A
C
I
F
I
C
Absent
T
L
A
N
T
I
C
 If the decimal point is present, start counting from the LEFT
 If the decimal point is absent, start counting from the RIGHT
Pacific/Atlantic Rule
 Step 3: Start counting on Pacific or Atlantic side
from the first NON-ZERO number. Count all
numbers after the first non-zero number including
zeros.
Pacific/Atlantic Rule
 Examples:
4 sig figs
a) 1234 = ________
4
b) 1204 = ________ sig figs
Absent 
Absent 
3 sig figs
c) 0.00234 = _______
Present 
d)
e)
3
1230 = ______ sig figs
5
1234.0 = ______ sig figs
Absent 
Present 
Pacific/Atlantic Rule
 Examples:
a)
b)
c)
4
4 sig figs
1204 = ________
3 sig figs
0.00234 = _______
1234 = ________ sig figs
3 certain digits – indicated by
lines on measuring device ;
1 estimated digit - in between
lines
3 certain ; 1 estimated
2 certain ; 1 estimated
(zero’s are place holders)
d)
3
1230 = ______ sig figs
2 certain ; 1 estimated
(zero is a place holder)
e)
5
1234.0 = ______ sig figs
4 certain ; 1 estimated
Using Sig. Figs. In Calculations
 Addition/Subtraction Rule
 Answer should contain least # of decimal places
 Multiplication/Division Rule
 Answer should contain least sig figs.
Do Now: Precision of Lab Instruments
1.
Record the following quantities to the correct number of
decimal places.
________ L
________ mL
_______ oC
2.
Convert your answer in A to milliliters: ________ mL
3.
Add your answer from A & B. Record using correct sig. figs.
________ mL
Scientific Notation
 Some numbers are very large or very small, so we
need a short hand notation.
Too large:
602,200,000,000,000,000,000,000
6.022 x 1023
Too small:
0.0000000000000000000000199
1.99 x 10-23
Scientific Notation
N x 10n
N is a number between 1 and 10
n is a positive or negative integer
if n is a negative number, the full number is a small decimal
if n is a positive number, the full number is a large number
3.69 x 10-4
1.245 x 105
________________
________________
Taking Measurements in
Chemistry
According to the Scientific Method
The Scientific Method
 Scientific Method: logical approach to solving
problems by…
a. Observing & collecting data
b. Formulating hypotheses
c. Testing hypotheses
d. Formulating theories
e. Publishing results
Two Types of Measurements
 Remember: observations about matter can be
categorized in two groups:
 Qualitative Data
 Quantitative Data
 Qualitative (think “quality”):
observations using words
 Quantitative (think “quantity”):
observations using numbers and units.
Studying a System
 System: specific portion of matter in a given region
of space that has been selected for study
 Microscopic or macroscopic level
 Variable: any condition that changes during an
experiment
 Independent: value being manipulated
 Dependent: result
Studying a System
 Experimental Control: conditions that remain constant
throughout (i.e. don’t change)
 Often many controlled portions of system
 Model: Explanation of how phenomena occur and how
data or events are related
 Visual
 Verbal
 Mathematical
 Ex: atomic model of matter
Studying a System
 Theory: broad generalization that explains a body of
facts or phenomena
 Used to predict results of new experiments
 Ex: kinetic molecular theory
Taking Measurements in
Chemistry
Graphing Measurements
Amount of
Fertilizer (g)
Plant Growth (cm)
6
5
9
9
15
17
23
22
Independent
Variable
Fertilizer
Dependent
Variable
Growth
Direct Relationship
 Title
 Appropriate scale
 Axis labeled
“Best fit” line
Direct
Relationships
• When 2 quantities divided
by each other gives a
constant value
• K (constant value) = Y/X
• Ex: Density
Inverse
Relationships
• When 2 quantities
multiplied by each other
gives a constant value
• K = XY
• Ex: Boyle’s Law
K = PV