Transcript Chapter 2 Measurements Guided PPT notes

What is Chemistry?
Chemistry is:
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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
Mass
Length
Time
Amount of
Substance
Temperature
Electric
current
Luminous
intensity
Symbol
kilogram
meter
second
mole
kg
m
s
mol
Kelvin
Ampere
K
A
candela
cd
What’s missing?
Note:
This is the SI
standard
unit but the
BASE unit is
the GRAM
Derived Units
•Combinations of base units
•Volume: amount of space taken up by an
object
• Most common unit: ________________
•Density: ratio of mass to volume
• Common units: ________________________
• Does not change for a given substance
Prefix
Symbol
Meaning
Numerical Value
Giga-
G
109
1,000,000,000
Mega-
M
106
1,000,000
Kilo-
k
103
1,000
Hecto-
h
102
100
Deka
da
101
10
BASE
g, l, m
100
1
Deci-
d
10-1
.1
Centi-
c
10-2
.01
Milli-
m
10-3
.001
Micro-
m
10-6
.000001
Nano-
n
10-9
.000000001
Practice Problems
1. 5.6 cm to m
2. 56 mg to g
3. 340 mm to cm
4. 1.2 ML to L
Factor-Label Method
(Dimensional Analysis)
Solve the following mathematical equation:
1
2
x
𝑚𝑖𝑙
ℎ𝑟
2
3
3
4
x
x
ℎ𝑟
𝑚𝑖𝑛
x
4
5
x
𝑚𝑖𝑛
𝑠𝑒𝑐
x
5
6
x
x
6
7
𝑘𝑚
𝑚𝑖𝑙
x
x
7
8
x
𝑚
𝑘𝑚
8
=
9
=
Using Factor-Label Method
•Sample Problems:
Converting 9.8 g to kg
Hint:
Converting 9.8 kg to g
Scientific Notation
Some numbers are very large or very small, so a short
hand notation is needed!
Too large:
602,000,000,000,000,000,000,000
Too small:
0.0000000000000000000000199
General Notation:
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
Practice
3.69 x 10-4
0.00000568
4.382 x 10-2
0.00436
8.37 x 10-7
0.00000000002
1.245 x 105
2460000000
8.7900 x 108
3456965
2.6091 x 102
3400450
Density Practice
•Density Formula
•Example Problem:
A piece of platinum metal with a density of
21.5 g/cm3 has a volume of 4.49 cm3. What is
its mass?
Measuring always involves some
estimation
__________________: A digit that
represents a mark on a scale or a nonblinking number on a display.
_______________________: A digit that
represents the space between the marks
on a scale or a blinking number on a
display.
24.62
what is certain?
what is uncertain?
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
• 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.
• Examples:
a) 1234 = ________ sig figs
b) 1204 = ________ sig figs
c) 0.00234 = _______ sig figs
d) 1230 = ______ sig figs
e) 1234.0 = ______ sig figs
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
Accuracy & Precision in Measurements
•Accuracy:
•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
•Is this accurate or precise?
Percentage Error
•Accuracy of an individual value (or average)
can be compared to the correct/accepted
value
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?
SCIENTIFIC METHOD
logical approach to solving problems
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Types of Observations
•Qualitative :
Example:
•Quantitative :
Example:
Physical Properties and Changes
physical property: characteristic that can be
observed or measured without changing the
identity of the substance.
• Ex:
physical change: change in a substance that
does not involve a change in the identity of
the substance.
• Ex:
Chemical Properties and Changes
chemical property: a substance’s ability to undergo
changes that transform it into different substances
• Ex:
chemical change: change in which one or more
substances are converted into different substance
• Ex:
Evidence of a Chemical
Change
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4.
5.
NOTE:
In an experiment…
System: specific portion of the experiment that has
been selected for study
Constant: experimental conditions that do not
change
Control: experimental condition that is used as a
standard for comparison
Variable: experimental condition that does change
SpongeBob loves to garden and wants to grow lots of pink
flowers for his pal Sandy. He bought a special Flower Power
fertilizer to see if it will help plants produce more flowers. He
plants two plants of the same size in separate containers with
the same amount of potting soil. He places one plant in a
sunny window and waters it every day with fertilized water. He
places the other plant on a shelf in a closet and waters it with
plain water every other day.
1. What are Spongebob’s constants in his experiment?
2. What are Spongebob’s variables in his experiment?
3. What did Spongebob do wrong?
4. What should SpongeBob do to test the effectiveness of
Flower Power fertilizer? Describe an experiment.
Amount of Fertilizer (g)
Plant Growth (cm)
6
5
9
9
15
17
23
22
 Title
 Appropriate scale
 Axis labeled
“Best fit” line
Direct
Relationships
• When 2 quantities
______________by each
other gives a constant value
• K (constant value) = Y/X
• Ex: Density
Inverse
Relationships
• When 2 quantities
_____________by each
other gives a constant
value
•K=XY
• Ex: Boyle’s Law
K = PV