CHEMISTRY July 31 st, 2012. 2 Brain Teaser: Dollar Bill What do think will happen if I dip a dollar...
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Transcript of CHEMISTRY July 31 st, 2012. 2 Brain Teaser: Dollar Bill What do think will happen if I dip a dollar...
CHEMISTRY
July 31st, 2012
2
Brain Teaser: Dollar Bill
What do think will happen if I dip a dollar bill in a 50% ethanol solution and light it on fire? Why? Demo Record Observations Was your prediction correct? Explain the science behind this
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Agenda
Brain Teaser Demo: Dollar Bill Lecture:
Introduction to Chemistry SI Units and Base Units Significant Figures
Homework Intro to Measurement Worksheet
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Unit 1 ObjectivesIntroduction to Chemistry
Define chemistry and matter Units of measurement
SI Units Base Units
Accuracy versus Precision Uncertainty in Measurement Significant Figures
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Introduction to Chemistry
Chemistry: The Central Science
Chemistry is the science that investigates and explains the structure and properties of matter.
Seeks to explain the submicroscopic events that lead to macroscopic observations
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Branches of Chemistry
Branch Area of Emphasis Examples
Organic chemistry
most carbon-containing chemicals
pharmaceuticals, plastics
Inorganic chemistry
in general, matter that does not contain carbon
minerals, metals and nonmetals, semi-conductors
Physical chemistry
the behavior and changes of matter and the related energy
changes
reaction rates, reaction
mechanisms
Analytical chemistry
components and composition of substances
food nutrients, quality control
Biochemistry
matter and processes of living organisms
metabolism, fermentation
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SI Units (Le Systéme Internationale) Scientists need to report data that can be
reproduced by other scientists. They need standard units of measurement.
Base Units• A base unit is a defined unit in a system of
measurement•There are seven base units in SI.
Units of measurement
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Base Units
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SIGNIFICANT FIGURES
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Significant Figures
Significant Figures
Digits in a measurement that have meaning relative to the equipment being used
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Significant Figures Place What is the increment on
the equipment?
What you know for sure.
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Significant Figures Digits with
meaningDigits that can be known
precisely plus a last digit that must be estimated.
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Graduated Cylinder
http://www.uwplatt.edu/chemep/chem/chemscape/labdocs/catofp/measurea/volume/gradcyl/gradcyl.htm
What are the units?
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Significant Figures
What do you notice?
Depends on type of equipment being used.
Depends on size of equipment used.
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Significant Figures
Raw Data Rules How do you
know how many sig figs?
1. All digits 1-9 are significant.
2. Zeros between significant digits are always significant.
3. Trailing 0’s are significant only if the number contains a decimal point
4. Zeros in the beginning of a number with a decimal point are not significant.
5. Zeros following a significant number with a decimal are significant.
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Significant Figures
Pacific to Atlantic Rule
Examples
Pacific = Decimal Present Start from the Pacific
(left hand side), every digit beginning with the first 1-9 integer is significant
20.0 = 3 sig digits0.00320400 = 6 sig digits1000. = 4 sig digits
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Significant Figures
Atlantic Rule to Pacific
Examples
Atlantic = Decimal Absent Start from the Atlantic
(right hand side), every digit beginning with the first 1-9 integer is significant
100020 = 5 sig digits1000 = 1 sig digits
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Practice
How many significant figures are in1. 400.02. 40003. 40044. 0.004
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Rally Rows How many significant figures are in1. 0.022. 0.0203. 5014. 501.05. 50006. 5000.7. 5050 01.00501. 503002. 5.0300
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Review Questions
Determine the number of significant figures in the following: 1005000 1.005 0.000125 1000. 0.02002 2002 200.200
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Review Questions
Determine the number of significant figures in:
72.3 g 60.5 g 6.20 g 0.0253 g 4320 g 0.00040230 g 4.05 x 10^5 g 4500. g
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Why do we use the metric system? Advantages
Simple to use Easy to convert from one unit to another
Dimensional Analysis Universal – used worldwide
By all scientists to communicate By all industrialized nations
Except United States U.S. loses billions of dollars in trade