Transcript Chapter One - Midway ISD

Chapter One
INTRODUCTION TO
CHEMISTRY
Monday
 Scientific method foldable
 Variables foldable
 Variables worksheet for homework
Section 1.2
Chemistry and Matter
 Chemistry- Study of matter
and changes it undergoes
 Matter- anything that has
mass and takes up space
 What’s the difference
between mass and weight???
 Mass- the amount of matter in
an object
 Weight- measure of matter
and effect of gravity on an
object
 What do the prefixes macroand micro- mean???
 Macroscopic- do not need a
microscope to see it
 Submicroscopic- so tiny that
parts can’t even be seen with
microscope (ex: atom)
 Submicroscopic events are
explained by making models
(a visual, verbal, or
mathematical explanation of
how things occur)
Section 1.3
Scientific Methods
Scientific
Method- a
systematic
approach
used in all
scientific
study
Steps of Scientific Method
1. Observation- the
act of gathering
information; may
be qualitative data
(from 5 senses) or
quantitative data
(numerical
information)
2.
Formulate hypothesis
(testable statement or
prediction about what has
been observed)
3.
Conduct Experiment (set of
controlled observations that
test hypothesis)
Variables
Independent and Dependent
Variables:
What they mean and how to use
them
What is a variable?
 In the design of a scientific experiment, a
variable is any factor that changes from
data group to data group.
 Scientific experiments are designed so
that the tested variables are the only
things that are supposed to change from
group to group; all other factors are to
remain constant
A handy Mnemonic for
Variables
Remember this phrase:
DRY MIX
Dependent Variable
 Dependent Variable
 is the variable that Responds to the
experimental design
 and is graphed on the Y-axis
Independent Variable
 The variable Manipulated by the
scientist
 is called the Independent variable
 and is graphed on the X-axis
Constant – variable that does not
change during an experiment
Control- standard for comparison
For Example:
 John wants to test how outside temperature
effects pea plant growth. He sets up four
identical greenhouse boxes where the only
difference in the plant environments will be
ambient temperature. One plant will grow at
10 °C. Another will grow at 20 °C which is
room temperature. A third will grow at 30 °C.
Finally, a forth will grow at 50 °C. After 30
days, the pea plants were measured for
growth.
Data Table
Temperature (in °C)
10
20
30
50
Pea Plant Growth (in cm)
13
45
37
4
Graph
Pea Plant Growth
Plant Growth (cm)
50
40
30
20
Pea Plant Growth (in cm)
10
0
10
20
30
Temperature (°C)
50
4. Analyze the data (more to
come in chapter 2)
5. Form a conclusion (judgment
based on the information
obtained; comparison of
hypothesis with actual results)
Theory- explanation supported
by many, many experiments
Ex: Big Bang Theory
Scientific Law- when the
same conclusion is found
many times with no
exceptions
Ex: Newton’s Law of Motion
Scientific Method and Law
Discussion
 Which variable was the independent
variable?
 Which variable was the dependent
variable?
 Which plant represented the control
group?
Tuesday
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Correct variables worksheet
Scientific notation
Significant figures
Accuracy and precision
Chapter 2
Data Analysis
2.1 Units of Measurement
 In 1960 the metric system was
updated and is called the
Systeme Internationale d’Unites
or the SI unit of measurement.
 Standard units of measurement
for ALL scientists to use
worldwide.
 Base Unit - unit of
measurement based on
an object or event in the
physical world
The standard kilogram is stored in a vault at the International Bureau of Weights and
Standards near Paris. It is made of a platinum-iridium alloy, and is shown here next to
an inch-based ruler for scale.
 Base Units:
1. Time: second (s)
2. Length: meter (m)
3. Mass: gram (g)
4. Temperature: Kelvin
(K)
5. Amount of substance:
mole (mol) an international
standard to measure an "amount
of stuff" aka Mole! It refers to the
number of atoms in 12 grams of
carbon 12 (6.022 x 1023)
Avagadro’s Number
 Derived Unit - A unit that is
a combination of base
units.
 There are hundreds of units
needed for measuring
“everything,” but they are all
derived from those base units.
1. Volume = L x W x H for a regularly
shaped solid
cubic meter (m3),cubic centimeter
(cm3) or cubic decimeter (dm3)
 Unit for volume: liter (L) for a liquid
 1 dm3 = 1 L
1 cm3 = 1 mL
2. Density- ratio that compares
the mass of an object to its
volume
 Units are grams per cubic
centimeter (g/cm3)
 1 ml
=
1 cm3
density = mass
volume
Density is a
property that can
be used to identify
an unknown
sample of matter.
Temperature
 Kelvin – SI base
unit for
temperature
 ºC + 273 = K
 K – 273 = ºC
 There are no
negative
temperatures in
Kelvin
2.2 Scientific Notation
 Scientific Notation- expresses
numbers as a multiple of two factors:
1. A number between 1 and 9
2. Ten is raised to a power (exponent).
 2.0 x 103  3 is the exponent
 2.0 x 103 = 2000
 .20 or 20 would be WRONG because
they are NOT numbers between 1 and
10!!
Scientific Notation Example
Count the number of places the decimal point moved and the
direction
 Convert 436289 to scientific notation.
1. Place decimal at end of number 436289.
2. Move decimal to place it behind the first number 4.36289
3. You moved the decimal 5 places left. 
4. If decimal moves left, the exponent is positive
5. The # of times the decimal was moved becomes the
exponent.
4.36289 x 105
If decimal moves left,
exponent is positive
if decimal moves right,
exponent is negative
 Convert .000872 to scientific notation
1. Move the decimal behind first number that is
NOT a zero. 0008.72
2. 8.72 You moved the decimal 4 places right.

3. The # of times the decimal was moved
becomes the exponent.
4. If decimal moves right, exponent is
negative.
5. The # of times the decimal was moved
becomes the negative exponent
8.72 x 10 – 4
To convert Scientific Notation to
Standard Notation Reverse the
above steps:
 If the exponent is positive move the decimal
to the right the same number of places as the
exponent.
 2.5 x 104 = 25 000
 If the exponent is negative move the decimal
to the left the same number of places as the
exponent.
 2.5 x 10-4 = .00025
 Adding, subtracting,
multiplying, and dividing in
Scientific Notation by using
the calculator
 Use “EE” or “exp” key on your
calculator to replace “ x 10^”
 Ex: 8.72 x 10-4 would be
8.72”EE”-4
Sect. 2.3: How reliable
are measurements?
 Accuracy – how close a
measured value is to an
accepted or true value
 Precision – how close a series of
measurements are to each other
 Compare to throwing darts
bottom of pg 36.
ACCURACY VS. PRECISION:
THIS CLOCK is more precise than THIS CLOCK
HOWEVER, if the actual time is 3:00, then the second clock is
more accurate than the first one.
 ACCURACY = HOW CLOSE A MEASUREMENT IS TO
THE TRUE VALUE
 PRECISION = EXACTNESS
Percent error – the ratio of an error to an
accepted value.
% error = experimental – accepted x 100
accepted value
Example:
Density of lead is 11.3, you had 10.3 in
your experiment.
Difference is 1
So
1 x 100 = 8.8%
11.3
Significant Figures
 Accuracy is limited by the
available tools.
 Sig figs are based on
instrument precision (numbers
can only be as exact as the
instrument is)
 Instruments must be calibrated
to assure accuracy.
 The “best” number is the one with
the most decimal places.
 So 3.54 g is MORE precise
than 3.5 g.
Significant figures - include all
known digits plus ONE estimated
digit.
Having Trouble with Sig Figs?
Try this:
1. Determine if the decimal point is “present” or “absent”.
2. Picture a map of the U.S. with the Pacific Ocean on the left and the
Atlantic Ocean on the right.
PACIFIC
Decimal present

ATLANTIC
Decimal absent

3. If the decimal point is “present”, imagine an arrow LEFT from the
Pacific Ocean pointing to the number. (Think “P” for “present” and
“Pacific”). 
4. If the decimal point is “absent”, imagine an arrow RIGHT from the
Atlantic Ocean pointing to the number (“A” for “absent” and
“Atlantic”). 
5. Start counting digits when the arrow hits a non-zero digit. Each digit
after that is significant.
EXAMPLES:
 .009120 has 4 sig figs (9 is the first nonzero digit counting from Pacific)
 1.050 has 4 sig figs (1 is the first nonzero digit counting from Pacific)
34005  has 5 sig figs (5 is the first nonzero digit counting from Atlantic)
1200  has 2 sig figs (2 is the first nonzero digit counting from Atlantic)
Rounding Numbers
 If last number is five or
greater, round up. 12.6 13
 If last number is less than
five, leave alone.
 12.2 12
Rounding Examples
12.27845
 Round to 3 significant figures
12.3
 Round to 5 significant figures
12.278
 Round to 4 significant figures
12.28
 Round to 2 significant figures
12
Math with Sig Figs
 When adding/subtracting,
answer will be rounded to
least number of decimal
places
28.0 cm
23.538 cm
+ 25.68 cm
77.218 cm so the answer must have
only one digit to the right of the
 When multiplying/dividing, answer will
be rounded to least number of sig
figs
3.20 cm x 3.65 cm x 2.05 cm = 23.944
cm3
all the factors have 3 sig figs
So the answer should have 3 sig figs
23.944 cm3 Becomes 23.9 cm3
Mult/Div Round to the
least number of sig figs
 2.50 m x 0.05 m x 5.00 m = 0.625 m3
3 sig figs
1 sig fig 3 sig figs
The answer should have one sig fig.
The answer would be 0.6 m3
(1200 cm ./. 3.0 cm) ./. 400.0 cm = 1
cm3
2 sig figs
2 sig fig
4 sig
figs
WEDNESDAY
 Practice significant figures and scientific
notation worksheet
Thursday
 Grade worksheet
 Do graph foldable
Section 2.4:
Representing Data
 A goal of many experiments is
to discover whether a pattern
exits.
 Data in a table may not show an
obvious pattern.
 Graphing can help reveal a
pattern.
 Graph – visual display of data
 3 types of Graphs
Circle graph/pie chart
Bar Graph
Line Graph
HOW TO CHOOSE WHICH
TYPE OF GRAPH TO USE?
When to Use . . .
. . . a Pie Chart.
 Pie charts are best to
use when you are
trying to compare
parts of a whole.
They do not show
changes over time.
When to Use . . .
. . . a Bar Graph.
Bar graphs are used
to show how a
quantity changes with
certain factors or to
compare things
between different
groups or to track
changes over time.
Bar graphs are best
when the changes are
larger.
When to Use . . .
. . . a Line graph.
Line graphs are used
to track changes over
short and long
periods of time.
When smaller
changes exist, line
graphs are better to
use than bar graphs.
Line graphs can also
be used to compare
changes over the
same period of time
for more than one
group.
Distance /Time Graph
Friday
 Measurement Lab