CHEMISTRY

CHEMISTRY

July 31st, 2012

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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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Ruler

http://www.funbrain.com/measure/

What are the units?

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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