Transcript CHE 104 Packet 1 - Kentucky Community and Technical

Packet 1
Chemistry & Measurements
last updated: 7/7/2015
CHE 140 Packet 1 - 1
Concept Area I: Terminology
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chemical
chemistry
experiment
hypothesis
observation
scientific method
theory
Celsius, ºC
centiconversion factor
cubic centimeter,
cm3
• density
• dimensional
analysis
• equality
• exact number
• gram
• Kelvin, K
• kilo• length
• liter
• mass
• measured number
• mega• meter
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metric system
micromillinanoscientific notation
second
significant
figures, sig figs
temperature
time
volume
weight
CHE 140 Packet 1 - 2
Concept Area II: Chemistry and
Chemicals
a. You must be able to explain the difference
between chemistry and other sciences.
b. You need be able to tell if something is a
chemical or not.
c. You should be able to explain the
difference between science and
technology.
CHE 140 Packet 1 - 3
Question . . .
What is Science?
There are many different ways to answer this
question!
Most scientists are inductivists, but they may
have other tendencies.
Karl Popper defined inductivism as (from http://en.wikipedia.org/wiki) –
“…new knowledge is the result of past observations and any knowledge
derived thereof is purely inductive. Therefore, it is fallible in the sense that
it is not capable of understanding new possibilities unless they have been
observed.”
What do you think is science?
CHE 140 Packet 1 - 4
Which of these do you think are sciences?
Astrology
History
Astronomy
Chemistry
Religion
Sociology
Acupuncture
Psychology
Mathematics
Biology
Physics
Archeology
Why or why not?
CHE 140 Packet 1 - 5
The differences between…
Physics
Chemistry
Biology
CHE 140 Packet 1 - 6
Why study science?
CHE 140 Packet 1 - 7
Now, why study specifically chemistry?
CHE 140 Packet 1 - 8
Another reason as to why study
specifically chemistry?
CHE 140 Packet 1 - 9
Science vs. Technology
• Technology is simply applied science, for
CH OH
example
CH Cl
2
• Science:
OH
O
2
O
OH
O
• sucralose is synthesized in a lab Cl
OH
OH
• lab tech misunderstands orders for “testing” the new
compound as “tasting” and discovers it is sweet
• eventually tests show it is safe for human consumption
• Technology
• sucralose (aka Splenda) is now sold as
a new artificial sweetener
CHE 140 Packet 1 - 10
CH2Cl
Concept Area III: The Scientific Method
a. You should be able to explain and apply
the scientific method and how it can lead
to the formation of theories and laws.
CHE 140 Packet 1 - 11
Scientific Knowledge is:
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Testable
Reproducible
Explanatory
• Predictive
• Tentative
An observation is made. A scientist attempts to explain the
observation by making a tentative hypothesis. This hypothesis
should help the scientist make predictions which he can test and
then reproduce. This is called experimentation. While
experimenting different types of data and observations are noted
and recorded. If the experiment gives data/observations are
consistent with the hypothesis, a theory can be generated.
If the experiment gives data/observations that clash with the
hypothesis, a new one must be generated!
CHE 140 Packet 1 - 12
Visualizing the
Scientific Method
CHE 140 Packet 1 - 13
Phlogiston Theory
• Observation: A candle placed within a closed space burns
for only a short time before being extinguished.
• Hypothesis: When something is burned it is being
decomposed into residue and phlogiston. Air can only
hold so much phlogiston. When the air within the closed
space is saturated, the candle goes out.
• Observation: Metals rust into residue in the air.
• Hypothesis: When something rusts it is being
decomposed into residue and phlogiston. Air simply
carries away the phlogiston.
• Clash
• Items burned weigh less.
• Items rusted weigh more.
• How if both involve loss of phlogiston?!
• New Hypothesis: Oxygen!
CHE 140 Packet P - 14
Concept Area II: Units of Measurement
a. For the following, you should be able to identify
the common units used in the metric system:
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length
mass
temperature
volume
density
time
b. You should be able to use the following metric
prefixes: mega-, kilo-, centi-, milli-, micro-, and
nano-.
c. You should also know that 1 cm3 = 1 mL.
CHE 140 Packet 1 - 15
Learn/memorize the metric units & symbols,
but metric to English conversions FYI only!
left table from Timberlake page 33
CHE 140 Packet 1 - 16
Metric Prefixes are Awesome! (
If you know
how to use!
)
• Metric prefixes are much easier to convert than
English. Let’s try!
• So, I am 68 inches tall which is 1,700 millimeters.
Now, convert to…
miles
and kilometers
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yards
and meters
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feet
and centimeters
.
• I am also 140 pounds which is 63.5 kilograms.
Now, convert to…
tons
and megagrams
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stones
and grams
.
ounces
and milligrams
.
• Notice that only the placement of the decimal
changed (unlike in the English system).
CHE 140 Packet 1 - 17
What do the metric prefixes
mean?
table Timberlake page 20
CHE 140 Packet 1 - 18
Metric Equalities......
Please also note that 1 cm3 = 1 mL
1 megameter
1 kilometer
1 centimeter
1 millimeter
1 micrometer
1 nanometer
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1,000,000 meters
1,000 meters
0.01 meters
0.001 meters
0.000001 meters
0.000000001 meters
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106 meters
103 meters
10–2 meters
10–3 meters
10–6 meters
10–9 meters
10–6 Mm
10–3 km
102 cm
103 mm
106 μm
109 nm
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0.000001 megameters
0.001 kilometers
100 centimeters
1,000 millimeters
1,000,000 micrometers
1,000,000,000 nanometers
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1 meter
1 meter
1 meter
1 meter
1 meter
1 meter
Make sure to pay attention to which one is the 1!
CHE 140 Packet 1 - 19
Metric Conversions Handout
Let’s do a little metric conversion!
1. 5.432 Mm
= ________ m
= ________ km
2. 5.432 kg
= ________ g
= ________ cg
3. 5.432 mL
= ________ L
= ________ mL
4. 5.432 ns
= ________ s
= ________ Ms
Try these at home (a bit harder because must convert before
doing the math).
5. 10 g + 0.050 kg = ________ g
6. 15 mm + 0.005 mm – 10,000 nm = ________ mm
7. (5km + 5,000m)÷(30s + 2.5min) = ________ km/hr
8. 20 cm × 15,000 mm × 0.5 m = ________ m3
CHE 140 Packet 1 - 20
Concept Area III: Scientific Notation
a. You need to be able to convert numbers to
and from scientific notation properly.
b. You need to be able to input numbers in
scientific notation into your calculator.
CHE 140 Packet 1 - 21
Scientific Notation
Remember this from before?
4. 5.432 ns=
s =
Ms
• Writing 5.432 nanoseconds into seconds and
megaseconds was pretty brutal with all those
zeroes, right?
• Using scientific notation will make it a lot
easier:
0.000000005432
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0.000000000000005432
We write 5.432×10–9 s instead of 0.000000005432 s
We write 5.432×10–15 Ms instead of
0.000000000000005432 Ms
CHE 140 Packet 1 - 22
Converting numbers to Scientific Notation
• Write the number so that one numeral is to the
left of the decimal and the other numerals are to
the right of the decimal.
• Multiply the number times 10 raised to the
appropriate power so that when the
multiplication is done we get our original
number.
Examples:
12
4548
– 0.235
0.000854
548611
CHE 140 Packet 1 - 23
Scientific Notation Handout
Converting numbers from Scientific Notation
Just move the decimal the number of places
indicated by the exponent on the 10!
Examples:
2
1. – 6.34×10
–5
2. 2.3586×10
8
3. 2.354×10
4.
1.56×10–1
CHE 140 Packet 1 - 24
Getting a calculator to do scientific notation!
There are different ways to enter numbers in
scientific notation into a calculator, here’s the
best way:
Let’s enter the following number: 1.23×104.
• Type 1.23
• Press EE or EXP (varies)
• Type 4
The calculator screen should display something
like: 1.23 04 or 1.23E4 or 1.23E4
Make sure you know how to do on your calculator!
See Scientific Notation and Calculators starting on page 12 in text for more help.
CHE 140 Packet 1 - 25
Concept Area IV: Significant Figures
a. You should be able to determine which numerals are
significant in a given number or measurement.
b. You must understand the significant figures rule about
defined numbers.
c. You need to be able to find the appropriate number of
significant figures to a problem after multiplying or
dividing (includes rounding).
d. Although you will not be held to addition/subtraction
rules, you need to avoid grievous sig fig errors in those
types of calculations.
e. You need to know when and how to round numbers.
CHE 140 Packet 1 - 26
Okay, if we’re given a number, how
many sig figs are there?
Easy! Count the number of digits present!
1. 1,259
2. 22.546
3. – 31
4. 78.3
Wait! That’s too easy – what about zeroes?
CHE 140 Packet 1 - 27
Okay, if we’re given a number with zeroes
in it, how many sig figs are there?
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Zeroes between significant digits are significant.
Zeroes to the right of a decimal are significant if
a significant digit is anywhere to the left of it.
A lone zero to the left of a decimal is not
significant, it is only there to draw attention to
the decimal. Same for zeroes to the right of the
decimal if no significant digit on left.
Zeroes at the end of a number without a
decimal may or may not be significant. To
avoid confusion, write in scientific notation!
CHE 140 Packet 1 - 28
Okay, if we’re given a number with at least
one zero in it, how many sig figs are there?
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7,405
892.8091
– 324.720
7,411.0
5.
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7.
8.
– 0.120
0.0086
0.9090
90210
CHE 140 Packet 1 - 29
Special Note about sig figs and Scientific Notation
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The great thing about scientific notation is
that whenever a zero is written in a
number in scientific notation, it is
significant!
Examples:
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2.
3.
4.
1.20×106
– 8.019×10–5
4.789000×109
3.7085400×10–2
CHE 140 Packet 1 - 30
How many sig figs in a measurement?
• When taking an analog
measurement, we
always approximate one
more digit than the
instrument marks; that
digit is the “uncertain”
digit.
• What do these pieces of
wood measure?
a)
b)
c)
Timberlake page 14
CHE 140 Packet 1 - 31
Significant Figures Handout
Multiplication and Division of Sig Figs
The final answer can only be as precise as the
number with the fewest sig figs.
1. 5.2 × 111.95 = 582.14  5.8×102
2. 103 × 92.69 = 9547.07  9.55×103
3. 1.2×105 × 2.3×10–2 = 2760  2.8×103
Now you try!
1. 546 × 25 =
2. 5.68×10–2 ÷ 0.1136 =
CHE 140 Packet 1 - 32
Addition and Subtraction of Sig Figs
The final answer can only be as precise as the
number with the fewest digits to the right of
the decimal.
2. 103
1.
5.2
+ 92.69
+ 111.95
117.15  117.2
195.69  196
Now you try!
4. 5.68×10–2
3. 546.0
– 0.12895
+ 25.15
CHE 140 Packet 1 - 33
How to Round
Just as we have been doing, if less than five
round down. If five or greater, round up.
Note! When we are calculating a problem, we
should do the entire calculation with all the
digits in our calculator. Rounding during the
calculation can cause our final answer to be
wrong. Only round to the proper number of
sig figs at the end of the calculation.
CHE 140 Packet 1 - 34
Exact Numbers
• Some numbers look like they have a limited
number of significant figures, but in fact, they
are defined or exact numbers.
• If we count something, it is an exact number.
• Some conversions have defined numbers in them.
• When we have a defined or exact number, we
do not use it to reduce the number of
significant figures in our final answer since
technically it has an infinite amount of sig
figs.
CHE 140 Packet 1 - 35
Concept Area V: Conversion Factors
and Dimensional Analysis
a. You need to be able to convert equalities to
conversion factors and vice versa.
b. You must be able to do calculations
showing all steps and conversion factors
with units – let your units help you!
CHE 140 Packet 1 - 36
Equalities versus Conversion Factors
• So, we know that 1 km = 1000 m, right? This is an
equality statement.
• In a calculation, we want a conversion factor. So, we
must covert the equality to a fraction:
1 km
1000 m
1000 m
1 km
or
.
• Notice that both these fractions equal one!
• All conversion factors must equal one.
• Otherwise they are not conversion factors!
• So, how do we know which fraction to use?
• Use dimensional analysis and let the problem tell us!
CHE 140 Packet 1 - 37
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Dimensional Analysis
Always do all calculations showing all steps with all units
– let the units help you do the calculation correctly!
(See Problem Solving beginning on page 37 of our Timberlake
text.)
In this class whenever we work a problem, we
always write out the units!
number in original units 
new units
 new number in new units
original units
Conversion Factor
If you don’t show all your work on exams, you will not get full
credit and may get no credit.
CHE 140 Packet 1 - 38
Units, are they really that important?
• Well, consider that NASA lost this $125
million Mars Climate Orbiter because NASA
thought the readout was in metric units, but the
numbers being sent back by the orbiter were in
English units. Thus the
orbiter was told to go
too low and entered the
atmosphere.
• A number without units
can be disastrous!
CHE 140 Packet 1 - 39
In other
words,
dimensional
analysis!
Timberlake page 29
CHE 140 Packet 1 - 40
Dimensional Analysis
Question: How many minutes are in 2.5 hours?
Step 1: Given unit?
Needed unit?
Step 2: Conversion plan?
Step 3: What conversion factors can we
write and which one is needed?
Step 4: Set up problem to cancel hours:
Step 5:
Timberlake page 10
Check that answer
is reasonable!
CHE 140 Packet 1 - 41
Dimensional Analysis & Conversion Factors Handout
Practice Time!
Use dimensional analysis to do the following
conversions. Remember to use sig figs and scientific
notation where appropriate!
1.
772 g = __________ kg
2.
0.45 m = __________ cm
3.
84 mm = __________ m
4.
1.255 kL = __________ L
Problems worked out on notes page.
CHE 140 Packet 1 - 42
Concept Area VI: Density
a. You need to know what density is and be
able to calculate it and use it in
calculations.
b. You should know the difference between
mass and weight.
c. You are not responsible for knowing
specific gravity.
CHE 140 Packet 1 - 43
Mass versus Weight
Earth
Mars
mass
1 gram piece of brass will be 1 gram on Earth or Mars
weight
a 1 gram piece of brass will weigh 1 gram on
Earth and 0.4 grams on Mars
decrease simply by going into space, but
So, our weight would decrease
our mass would remain the same.
How can we lose mass?
Earth
Earth’s moon
CHE 140 Packet 1 - 44
Density = Mass ÷ Volume
• Let’s take a moment to look at density.
• Density is a measure of how tightly the particles
of an object are packed together.
• Tightly packed = high density
• Loosely packed = low density
• We calculate density by dividing the mass of a
sample by its volume. So, the normal units for
liquid densities are grams per milliliter (g/mL).
CHE 140 Packet 1 - 45
Why does a cork float and a piece of lead sink in water?
Timberlake page 33
CHE 140 Packet 1 - 46
Density
• Take the same volume of
lead and aluminum:
• Lead is tightly packed and
thus has high density.
• Aluminum is loosely
packed and thus has low
density.
• Which one will have more
mass and thus weigh
more?
CHE 140 Packet 1 - 47
Density = Mass ÷ Volume
So, if the density of mercury, Hg, is 13.6 g/ml:
1.
2.
If we have 13.6 g of Hg, how many milliliters do we have?
How many cm3 do we have?
If we have 1.00 mL of Hg, how many grams do we have?
Notice then how density is sort of a bridge between
and
!
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If we know density and mass, we can calculate volume.
If we know density and volume, we can calculate mass.
If we know mass and volume, we can calculate density.
CHE 140 Packet 1 - 48
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Remember Dimensional Analysis!
new units
number in original units 
 new number in new units
original units
Conversion Factor
Example: Suppose we have a post-1982 penny with a
density of 7.40 g/mL and a mass of 2.90 g. What is
its volume in mL?
1 mL
2.90g 
 0.392mL
7.40g
See how nicely the units cancel and help make sure we
did the problem correctly?
CHE 140 Packet 1 - 49
Density = Mass ÷ Volume
How do we determine the density of an solid,
like an irregular cylinder of zinc?
Timberlake page 35
CHE 140 Packet 1 - 50
Density = Mass ÷ Volume
How do we determine the density of an solid,
like an irregular cylinder of zinc?
1. Determine the mass of it by putting on a scale!
done: 68.60 g
Timberlake page 35
CHE 140 Packet 1 - 51
Density = Mass ÷ Volume
How do we determine the density of an solid,
like an irregular cylinder of zinc?
1. Determine the mass of it by putting on a scale!
done: 68.60 g
2. Determine the volume of it. How?
by displacement
done: 45.0 mL – 35.5 mL = 9.5 mL
CHE 140 Packet 1 - 52
Now some density problems…
Given that the density of a substance is 3.26 g/cm3,
determine the following. Remember sig figs and use
scientific notation where appropriate!
1.
3.26 g/cm3 = ___________ g/mL
2.
1.00 cm3 = ___________ mg
3.
4.56 g = ___________ mL
4.
3.26 g/cm3 = ___________ kg/m3
Problems worked out on notes page.
CHE 140 Packet 1 - 53
The End of Packet 1
Any Questions?
CHE 140 Packet 1 - 54