Transcript What is Chemistry?

Safety
MSDS
Scientific Method
Powers of 10
Accuracy vs. Precision
Significant Digits
Dimensional Analysis
What is Chemistry?
Chemistry is the study of matter and the
changes it undergoes. It is a science of
inquiry.
We need chemistry to understand
medications, cooking, and
transportation issues.
Reasons to Understand
Chemistry
• Be a better informed citizen so that you
understand news stories about
chemicals.
• So that you understand drug and
chemical interactions and can make
better choices about your life.
Safety Review
http://www.youtube.com/watch?v=xJ
G0ir9nDtc
MSDS
The Most Misunderstood
Words in Science
• Hypothesis, theory, skeptic, model,
nature vs. nurture, significant, natural
•
•
•
•
Observation
Hypothesis
Experiments
Conclusion
– Model
– Theory
– Law
Theory vs. Law
• Scientific theories
explain why
something
happens.
• Scientific laws
explain how
something
happens.
• As technology
changes, theories
can be improved.
• Laws don’t
change.
Inference vs. Observation
• Observations are
made using your
senses.
• Inferences are
made by
comparing past
experiences.
Hypothesis vs. Theory
• Hypothesis
– Explanation of why
something happens
that must be
testable.
– Requires extensive
testing after which
it may become a
theory.
• Theory
– Explanation of
why something
happens that has
been tested many
times, is well
established, and
highly reliable
Models
• We used models to explain hypotheses.
• What are some kinds of models that you
know?
• Pure Research
– Research for the
sake of knowledge
• Applied Research
– Solve a specific
problem
– Includes technology
Standards of Measurement
When we measure, we use a measuring tool to
compare some dimension of an object to a
standard.
For example, at one time the
standard for length was the king’s
foot. What are some problems
with this standard?
SI measurement
• Le Système international d'unités
• The only countries that have not
officially adopted SI are Liberia (in
western Africa) and Myanmar
(a.k.a. Burma, in SE Asia), but
now these are reportedly using
metric regularly
• Metrication is a process that does
not happen all at once, but is
rather a process that happens
over time.
• Among countries with non-metric
usage, the U.S. is the only country
significantly holding out. The U.S.
officially adopted SI in 1866.
The Base SI Units
Quantity
Base Unit
Length
Mass
Time
Temperature
Amount
Electric Current
Luminous Intensity
Meter (m)
Kilogram (kg)
Second (s)
Kelvin (K)
Mole (mol)
Ampere (A)
Candela (cd)
15
Derived Units
Two or more base units combined mathematically.
1. Volume v = length x width x height
•
volume = meters x meters x meters
• Three base units
2. Density D = mass/volume
• Density = kilograms/meters x meters x meters
• Four base units
3. Speed s = distance/time
• Speed = meters/seconds
• Two base units
Measuring Volume
Volume
Remember
to read the
volume at
the bottom
of the
meniscus!
Powers of 10
• http://vimeo.com/6150677
• See what powers of 10 look like on the
above video!
• Or explore it on your own with this
website:
http://htwins.net/scale2/
SI Prefixes
Prefix Symbol Factor
Scientific
Notation
Example
Giga
G
1,000,000,000
109
Gigameter (Gm)
Mega
M
1,000,000
106
Megagram (Mg)
Kilo
k
1,000
103
Kilometer (km)
Deci
d
1/10
10-1
Deciliter (dL)
Centi
c
1/100
10-2
Centimeter (cm)
Milli
m
1/1000
10-3
Milligram (mg)
Micro
µ
1/1,000,000
10-6
Microgram (µg)
Nano
n
1/1,000,000,000
10-9
Nanosecond (ns)
pico
p
1/1,000,000,000,000
10-12
Picometer (pm)
Metric Prefixes
Chemistry In Action
On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mars’
atmosphere 100 km lower than planned and was destroyed by
heat.
1 lb = 1 N
1 lb = 4.45 N
“This is going to be the
cautionary tale that will be
embedded into introduction
to the metric system in
elementary school, high
school, and college science
courses till the end of time.”
What is Scientific Notation?
• Scientific notation is a way of
expressing really big numbers or
really small numbers.
• For very large and very small
numbers, scientific notation is more
concise.
To change standard form to
scientific notation…
• Put one non-zero digit to the left of the
decimal point.
• Count the number of decimal places the
decimal point “moved” from the original
number. This will be the exponent on the 10.
• If the original number was less than 1, then
the exponent is negative. If the original
number was greater than 1, then the
exponent is positive.
Examples
1. Given: 289,800,000
2. Move: 2.898 (moved 8 places)
3. Answer: 2.898 x 108
1. Given: 0.000567
2. Move: 5.67 (moved 4 places)
3. Answer: 5.67 x 10-4
Examples
16. Express the following in scientific
notation.
a.
b.
c.
d.
e.
f.
g.
h.
700 m
38,000 m
4,500,000 m
685,000,000,000 m
0.0054 kg
0.00000687 kg
0.000000076 kg
0.0000000008 kg
Examples
Solve the following problems on your
calculator:
a.
b.
c.
d.
e.
f.
g.
h.
5 x 10-5m + 2 x 10-5m
7 x 108m – 4 x 108m
4.39 x 105kg – 2.8 x 104kg
5.36 x 10-1kg – 7.40 x 10-2kg
(4 x 102cm) x (1 x 108cm)
(1 x 103cm) x (5 x 10-1cm)
(6 x 102g) ÷ (2 x 101cm3)
(4 x 10-3g) ÷ (2 x 10-2cm3)
Dimensional Analysis
• A method of problem-solving that
focuses on the units used to describe
matter that uses conversion factors.
• There are always two ways to show a
conversion factor!
1m = 100 cm or 100 cm = 1 m
1 km = 1000 m or 1000 m = 1 km
1 hr = 60 min or 60 min = 1 hr
How many minutes are in 2.5 hours?
Conversion factor
2.5 hr
60 min
1 hr
= 150 min
cancel
By using dimensional analysis, the UNITS ensure that you
have the conversion right side up, and the UNITS are
calculated as well as the numbers!
Examples
19. Make the following conversions using
the prefix chart on #14.
a. Convert 360 s to ms
b. Convert 4800 g to kg
c. Convert 5600 dm to m
d. Convert 72 g to mg
Wait a minute!
What is wrong with the following setup?
1.4 day 1 day
24 hr
60 min 60 sec
1 hr
1 min
Can you hit the bull's-eye?
Three targets
with three
arrows each to
shoot.
How do they
compare?
Both
accurate
and precise
Precise
but not
accurate
Neither
accurate nor
precise
Accuracy is how close your measurements are
to the accepted value.
Precision is how close your measurements are
to each other.
Percent Error
• Percent error shows how accurate your
measurement is:
% Error = Accepted Value – Experimental Value x100
Accepted Value
Significant Figures
The numbers reported in a
measurement are limited by the
measuring tool
Significant figures in a measurement
include the measured digits plus one
estimated digit
Rules for Significant Digits
• RULE 1. All non-zero digits in a
measured number are significant.
• RULE 2. Zeros between non-zero
numbers are significant.
• RULE 3. Other zeros are only
significant if they follow both a decimal
point and a non-zero digit.
Examples
• 27. How many significant digits are in each of the
following measurements?
a. 508.0L
e. 0.000482mL
b. 820,400.0L
f. 3.2587 x 10-8g
c. 707,000kg
g. 0.0084mL
d. 0.049450s
h. 1.0200 x 105kg
Significant Numbers in Calculations
 A calculated answer cannot be more precise than
the measuring tool.
 A calculated answer must match the least precise
measurement.
 Significant figures are needed for final answers
from
1) adding or subtracting
2) multiplying or dividing
Adding and Subtracting
The answer has the same number of decimal
places as the measurement with the fewest
decimal places.
25.2
one decimal place
+ 1.34 two decimal places
26.54
answer 26.5 one decimal place
Multiplying and Dividing
Round (or add zeros) to the calculated
answer until you have the same number
of significant figures as the measurement
with the fewest significant figures.
a. 2.19 X 4.2 = 9.198 → 9.2
b. 4.311 ÷ 0.07 = 61.5857 → 60
c. 2.54 X 0.0028
= 2.347 → 2.3
0.0105 X 0.060
Examples
30. Solve and round to the appropriate number of significant digits.
a. 43.2cm + 51.0cm + 48cm = __________________
b. 0.0487mg + 0.05834mg + 0.0048mg = ____________________
c. 5.236cm – 3.14cm =___________________
d. 24m x 3.26m =________________________
e. 53.0m x 1.53m =___________________________
f. 102.4m ÷ 51.2s =________________________
g. 168m ÷ 58s =_______________________