Chemistry 111, Section 4

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Chemistry 111, Section 4

• Prof. Peter Khalifah

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Study guide

• 6 hrs per week for this class (lab not included)
• 80 problem solving / 20 reading

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Your education
paid up front, results not guaranteed
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Evolution

• Evolution physical characteristics of organisms
  are hereditary, and are generally controlled by
  DNA.

Importance Agriculture Medicine
Scientific method American spirit
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Faith vs. Science

• Faith belief in the absence of experimental
  evidence
• Science belief in the results of verifiable
  experimental evidence

• The value of science is its predictive ability

• Science also requires faith atoms?

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Homework assignment

• OWLs generally due Mon / Thur
• Required OWLs
• Intro to OWL (for Fri), Sig. Figs. (for Mon)
• Optional OWLs
• Math refresher, tutorials

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• 125 215 by lower clock

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Handout

• Syllabus

Posted on website http//courses.umass.edu/chem11
1k/
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Tools of the trade
The quest for efficiency
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What is the volume of liquid??
Specifying the significance of a
measurement Write all digits that are known
with certainty, and the first digit that is
uncertain.
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Significant figures
How many sig figs are in a number? Rule 1 All
non-zero numbers are significant

• 1498.25
• 17.3
• 17.300

• 6
• 3
• 5

Sig figs are a statement of accuracy
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Significant figures big numbers
How many people live in this county?
152,251 in 2000 155,101 in 2003 (estimated) ???
in 2005
158,000
Rule 2 For numbers without a decimal, trailing
zeros are NOT significant
How many people live in the USA today?
281,421,906 in 2000 290,809,777 in 2003
(estimated) ??? in 2005?
300,000,000
Some numbers as written imply an incorrect degree
of accuracy
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Significant figures small numbers
What is the weight of a single cell?
One cell weighs 0.00000051098620337 grams
One cell weighs 0.0000005110 grams
Rule 3 For numbers smaller than one, leading
zeros are NOT significant
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Scientific notation

• Lets us express sig figs unambiguously.
• 300,000,000
• 301,000,000
• 1498.25
• 17.3
• 17.300

3.00 x 108 (vs 3 x 108) 3.01 x
108 1.49825 x 102 1.73 x 101 1.7300 x 101
Exponential notation
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Scientific vs. exponential notation

• Scientific Exponential
• 4.178 x 103 4.178E3
• 9.14 x 10-21 9.14E-21

Is 10E2 the same as 102 ?
Only appropriate time to use exponential notation
is when talking to a computer!
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Significant figures

• How many sig figs do we keep while doing
  mathematical operations?
• Addition/Subtraction keep only digits specified
  on both numbers
• Multiplication/Division keep minimum number of
  sig figs

872.16 95.0 967.16
101 - 2.146 98.854
12.7 x 58.1 737.87
44.98 / 1.7 26.4588235