Welcome to Chemistry 0485

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Welcome to Chemistry 0485

• Introductions
• Books and Syllabus
• Expectations
• Basics of Numbers/Measurements
• Fundamentals of Chemistry

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Measurement
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Measurement vs. Numbers

• Measurements
• Science is based on measurements
• All measurements have
• Magnitude
• Uncertainty
• Units

• Numbers
• Mathematics is based on numbers
• Exact numbers are obtained by
• Counting
• Definition (i.e. one dozen 12)

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Prefixes Used in the Metric System

• Giga G 109 or 1,000,000,000
• Mega M 106 or 1,000,000
• Kilo k 103 or 1,000
• Deci d 10-1 or 0.1
• Centi c 10-2 or 0.01
• Milli m 10-3 or 0.001
• Micro u 10-6 or 0.000001
• Nano n 10-9 or 0.000 000 001
• Pico p 10-12 or 0.000 000 000 001
• Femto f 10-15 or 0.000 000 000 000 001

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SI Units

• Length meter
• Mass amount of material in an object
• Weight mass affected by gravity
• Temperature
• Celsius Scale (based on C)
• Kelvin Scale (based on absolute zero)
• Conversion K C 273.15

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Derived SI Units

• A derived unit is something you cannotmeasure
  directly you have to calculate it.
• Volume
• Units ml or cm3
• Vol. of a regular solid length x width x height
• Vol. of an irregular solid volume of liquid
  displaced
• Vol. of a cylinder 2(pi)R
• Density mass/volume
• Units g/mL or g/L

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Uncertainty in Measurement

• Exact versus inexact numbers
• Exact Those whose values are known exactly.
• Examples?
• Counted values like 12 eggs in one dozen
• The number 1 in conversions, like 1m100cm

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Uncertainty in Measurement

• Exact versus inexact numbers
• Inexact Numbers obtained by measurements.
  They are inexact because they always contain
  uncertainty.
• Why would they contain uncertainty?
• Limitations of measuring instruments
• Human error

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Uncertainty in Measurement

• Precision and Accuracy
• Precision measure of how closely individual
  measurements agree with each other.
• Accuracy measure of how closely individual
  measurements agree with a true value.

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Uncertainty in Measurement

• Are these measurements PRECISE?
• Are these measurements ACCURATE?

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Uncertainty in Measurement

• Significant Figures
• Indicates the exactness of measurements
• Significant is not the same as important
• 1 and .001 have the name number of significant
  figures. Clearly the zeros in .001 are important,
  but they are not significant. Significance
  refers to the exactness of the measurement.

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Uncertainty in Measurement

• What is the difference between 7g and 7.00g?
• Which measurement would have the most sig. figs?
  
• 1000 miles
• 1.56 miles
• .000045 miles
• Answer 1.56 miles with 3 sig. figs

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Significant Figure Guidelines

• Flashcard Alert!
• 1. Nonzero digits are always significant.
• 2. Zeros trapped between nonzero numbers are
  always significant. (2002 has 4 significant
  figures)
• 3. Zeros at the beginning of a numberare never
  significant they just showthe position of the
  decimal point. (.005 has only 1 significant
  figure)

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Significant Figure Guidelines

• 4.Zeros that fall at the end of a number after a
  decimal point are always significant. (.00500 has
  3 sig figs)
• 5.Numbers at the end of a number are only
  significant if the follow a decimal point! To be
  sure, convert to scientific notation.
• -700 has 1 significant figure -7.00 x 102 has
  3 significant figures

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Stop and Practice!
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Significant Figures in Calculations

• Multiplication and Division
• Base your answer on the number with the fewest
  significant figures!
• Round your final answer if it has more than the
  allowed number of significant figures.

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Example of Multiplication

• If you multiply 1.23 and 4.567, you get 5.61741.
• 1.23 has three significant figures,
• 4.567 has four.
• Solution? Round your answer to three significant
  figures! Write the answer as 5.62.

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Significant Figures in Calculations

• Addition and Subtraction
• Base your answer on the number with the fewest
  significant figures to the right of the decimal
  point.
• Round your final answer if it has more than the
  allowed number of significant figures.

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Example of Addition

• If you add 1.23 and 4.567, you get an answer of
  5.797. But 1.23 and 4.567 have different number
  sig figs after the decimal. Here you are
  limited to two sig figs after the decimal point.
  Round your answer like this! 1.23 4.5675.797 so
  ?5.80

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Rounding Off Significant Figures

• When the answer to a calculation contains too
  many significant figures, it must be rounded off.
  There are 10 digits that can occur in the last
  decimal place in a calculation (0,1,2,3,49).
• If the digit is smaller than 5, drop it and leave
  the remaining number unchanged. Example 1.684
  becomes 1.68.
• If the digit is 5 or larger, drop it but add 1 to
  the previous digit. Example 1.247 becomes 1.25.

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Scientific Notation

• Scientists use shorthand to express very large
  numbers called scientific notation.
• Scientific Notation is based on powers of the
  base number 10.
• We write 123,000,000,000 as 1.23 x 1011

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Scientific Notation

• We call the first number the coefficient. It must
  be 1-9.
• The second number is called the base. It must
  always be 10. The base number 10 is always
  written in exponent form. In the number 1.23 x
  1011 the number 11 is referred to as the exponent
  or power of ten.

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Scientific Notation

• To write a number in scientific notation, put the
  decimal after the first digit and drop the
  zeroes.

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Scientific Notation

• The coefficient for 123,000,000,000 is 1.23
• To find the exponent count the number of places
  from the decimal to the end of the number.
• In 123,000,000,000 there are 11 placesso we
  write 123,000,000,000 as1.23 x 1011

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Scientific Notation

• Numbers less smaller than 1 work the same way,
  but you get a negative exponent. A millionth of a
  second (0.000001 sec. ) is 1.0 x 10-6
• It might look like this on your calculator
  1.0E-6 or 1.0-6

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Scientific Notation Recap

• For numbers greater than 1, your exponent will be
  POSITIVE. (Youre moving the decimal point to the
  LEFT.)
• For numbers less than 1, your exponent will be
  NEGATIVE. (Youre moving the decimal point to the
  RIGHT.)

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Units of Measurement

• Metric System versus English System
• SI system
• Mass - measured in kilograms (kg)
• Length - measured in meters (m)
• Time - measured in seconds (s or sec)
• Electric current - measured in Amps (A)
• Temperature - measured in Kelvin (K)
• Luminous intensity - measured in cadelas (cd)
• Amount of substance - measured in moles (mol)
• The meter was originally defined as 1/10 000 000
  of the distance between the North Pole and the
  Equator