CHEMISTRY = Chemistry is the study of matter and energy and the interactions between them.
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Transcript of CHEMISTRY = Chemistry is the study of matter and energy and the interactions between them.
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CHEMISTRY =
Chemistry is the study of matter and energy and the interactions between them
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Studying science requires that one be a good observer.
observation inference
involves a judgmentor assumption
uses the fivesenses
Observations
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DataObservations are also called data.
There are two types of data.
qualitative data quantitative data
descriptions; measurements; no numbers must have numbers
and UNITS
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How good are the measurements?
• Scientists use two word to describe how good the measurements are-
• Accuracy- how close the measurement is to the actual value.
• Precision- how well can the measurement be repeated.
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Differences
• Accuracy can be true of an individual measurement or the average of several.
• Precision requires several measurements before anything can be said about it.
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PRECISION VERSUS ACCURACY
Problem : Identify if the following figures are either accurate or precise or
both:
• A._________ B._________ C.__________ D._________A ? Both A & P Only
Precise Neither A/P
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In terms of measurement
• Three students measure the room to be 10.2 m, 10.3 m and 10.4 m across.
• Were they precise?• Were they accurate?
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Data
• Must be organized
• Can be organized into charts, tables, or graphs
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Line Graphshows continuous change
0
10
20
30
40
50
60
Jan Feb Mar Apr
Month
Sh
are
Pri
ce (
$)
Stock Price over Time
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Elements of a “good” line graph
• axes labeled, with units
• use the available space
• title• neat
Temp. v. Vol. for a Gas at Constant Pressure
0123456789
10
120 140 160 180 200 220 240
Temp. (K)
Vo
lum
e (
L)
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How to read a graph• Interpolate - read
between data points• What volume would the
gas occupy at a temperature of 150 K?
• Extrapolate - read data beyond data points
• What volume would the gas occupy at a temperature of 260 K?
• Which do you have more confidence in? Why?
Temp. v. Vol. for a Gas at Constant Pressure
0123456789
10
120 140 160 180 200 220 240
Temp. (K)
Vo
lum
e (
L)
(independent variable)
(dep
ende
nt v
aria
ble)
7 L
~4 L
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Line Graph
Mass (g)
Age (Year of Penny)
Mass (g)
Age (Year of Penny)
Mass (g)
Age (Year of Penny)
Mass (g)
Age (Year of Penny)
How does the mass of a penny change with age?
A B
C D
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Hypothesis
• A suggested solution to the problem.
• Must be testable• Sometimes
written as If…Then… statements
• Predicts an outcome
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Scientific Law vs. Scientific Theory
Law of Gravity
A theory tries to explain whyor how something happens.
A law states what happens.
Theory of GravityAtomic TheoryCollision Theory of Reactions
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Significant Figures
• Numbers in science are used to measure • Measurements can only be taken to the least
precise level of the measuring device
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4. 0.080
3. 5,280
2. 402
1. 23.50
Significant Figures
Counting Sig Fig Examples
1. 23.50
2. 402
3. 5,280
4. 0.080
4 sig figs, rule #
3 sig figs, rule #
3 sig figs , rule #
2 sig figs , rule # Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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Rounding rules
• Look at the number behind the one you’re rounding.
• If it is 0 to 4 don’t change it.• If it is 5 to 9 make it one bigger.• Round 45.462 to four sig figs.• to three sig figs.• to two sig figs.• to one sig figs.
45.4645.54550
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Watch the Sig Figs
• When rounding, you don’t change the size of the number.
• You should end up with a number about the same size (magnitude).
• Use place holders- they’re not significant.– Round 15253 to 3 sig figs– Round 0.028965 to 3 sig figs 15300
0.0290
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Significant figures (cont’d)
• 98.748 __________
• 950.9 __________
• 0.08 __________
• 0.058 __________
• 8.097 __________
• 74.99 __________
Round to the tenths Round to the hundredths
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# of sig figs in the answer is based on the # sig figs in least precise measurement.
Which is the least precise?7.22m or 7.22555 m
Significant FiguresCalculating with Sig Figs
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Significant FiguresCalculating with Sig Figs
– Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer.
• (This is the measurement that is the LEAST precise)
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g 7.9 mL 350 g
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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Significant FiguresCalculating with Sig Figs
– Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.
• (This is the measurement that is the LEAST precise)
(13.91g/cm3)(23.3cm3) = 324.103g
324 g
4 SF 3 SF3 SF
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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MEASURING WITH ACCURACY AND PRECISION
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Practice Measuring Length
4.5 cm
4.54 cm
3.0 cm
Timberlake, Chemistry 7th Edition, page 7
cm0 1 2 3 4 5
cm0 1 2 3 4 5
cm0 1 2 3 4 5
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How to measure Mass
100 200 400300 5000
0 10 20 30 40 50 60 70 80 90
0 1 2 3 4 5 6 7 8 9 10
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How to Measure Volume
50
40
30
20
10
0
Graduated Cylinder
Come in variety of sizes
measure milliliters
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• Meniscus - the curve the water takes in the cylinder
How to Measure Volume50
40
30
20
10
0
Meaure at the bottom of the meniscus.
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The Metric System
• The units of measurement in science are from the metric system.
• The three most common are mass (grams), volume (liters), and length (meters)
• The metric system utilizes these base units then adds prefixes to indicate values increasing or decreasing by a factor of 10.
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Converting
k h D d c m• how far you have to move on this chart,
tells you how far, and which direction to move the decimal place.
• The box is the base unit, meters, Liters, grams, etc.
. . . . . . .
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Converting
k h D d c m• In order to convert from one unit to another, set
up a proportion where the unknown (X) and the given (G) with their respective units of measurement are on top and the conversion factors are under in the right place.
. . . . . . .
)(unitfactor
)(
)(unitfactor
) (unit X
2
2
1
1 unitG
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Metric Conversions
• 10cm = _____m
• 1mm = _____cm
• 10dL = _____mL
• 5 liters = _____mL
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Metric Conversions
• 0.1dL = _____cL
• 1Kg = _____g
• 100 mm = _____cm
• 300,00mg = _____g
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What about micro- and nano-?
• The jump in between is 3 places• Convert 15000 μm to m
• Convert 0.00035 cm to nm
k h D d c m μ n3 3
. . . . . . . . .
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Scientific Notation
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How wide is our universe?
210,000,000,000,000,000,000,000 miles(22 zeros)
This number is written in decimal notation. When numbers get this large, it is easier to write them in
scientific notation.
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Powers of 10
• http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
• http://www.powersof10.com/
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Scientific Notation
A number is expressed in scientific notation when it is in the form
a x 10n
where a is between 1 and 10and n is an integer
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Write the width of the universe in scientific notation.
210,000,000,000,000,000,000,000 milesWhere is the decimal point now?
After the last zero.Where would you put the decimal to make
this number be between 1 and 10?Between the 2 and the 1
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2.10,000,000,000,000,000,000,000.
How many decimal places did you move the decimal?
23When the original number is more than 1,
the exponent is positive.The answer in scientific notation is
2.1 x 1023
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1) Express 0.0000000902 in scientific notation.
Where would the decimal go to make the number be between 1 and 10?
9.02The decimal was moved how many places?
8When the original number is less than 1, the
exponent is negative.9.02 x 10-8
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Write 28750.9 in scientific notation.
1. 2.87509 x 10-5
2. 2.87509 x 10-4
3. 2.87509 x 104
4. 2.87509 x 105
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2) Express 1.8 x 10-4 in decimal notation.0.00018
3) Express 4.58 x 106 in decimal notation.4,580,000
On the graphing calculator, scientific notation is done with the button.
4.58 x 106 is typed 4.58 6
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4) Use a calculator to evaluate: 4.5 x 10-5
1.6 x 10-2
Type 4.5 -5 1.6 -2
You must include parentheses if you don’t use those buttons!!
(4.5 x 10 -5) (1.6 x 10 -2)
0.0028125Write in scientific notation.
2.8125 x 10-3
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5) Use a calculator to evaluate: 7.2 x 10-9
1.2 x 102
On the calculator, the answer is:6.E -11
The answer in scientific notation is 6 x 10 -11
The answer in decimal notation is 0.00000000006
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6) Use a calculator to evaluate (0.0042)(330,000).
On the calculator, the answer is1386.
The answer in decimal notation is 1386
The answer in scientific notation is 1.386 x 103
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7) Use a calculator to evaluate (3,600,000,000)(23).
On the calculator, the answer is:8.28 E +10
The answer in scientific notation is 8.28 x 10 10
The answer in decimal notation is 82,800,000,000
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Write (2.8 x 103)(5.1 x 10-7) in scientific notation.
1. 14.28 x 10-4
2. 1.428 x 10-3
3. 14.28 x 1010
4. 1.428 x 1011
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Write in PROPER scientific notation.(Notice the number is not between 1 and 10)
8) 234.6 x 109
2.346 x 1011
9) 0.0642 x 104
on calculator: 6426.42 x 10 2
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Write 531.42 x 105 in scientific notation.
1. .53142 x 102
2. 5.3142 x 103
3. 53.142 x 104
4. 531.42 x 105
5. 53.142 x 106
6. 5.3142 x 107
7. .53142 x 108