Chapter%201:%20Introduction

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Chapter 1 Introduction
Chemistry 1020 Interpretive chemistry Andy
Aspaas, Instructor
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What is chemistry?

• The science that deals with the materials of the
  universe and the changes that these materials
  undergo.
• Chemistry in relation to other sciences

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Chemistry around us

• Advances from chemistry
• Medicine
• Agriculture
• Energy
• Plastics
• Problems from chemistry?

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Scientific problem solving

• The scientific method process behind all
  scientific inquiry
• Flexible, changes when new information is learned
• Start with a question, problem or observation
• Hypothesis possible explanation
• Experimentation controlled process of gathering
  new information
• Observations, do they support the hypothesis?
• Theory a tested hypothesis, can still be revised

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Law vs. theory

• Natural law generally observed behavior, result
  of measurements
• Theory our attempt to explain why certain
  behaviors happen
• Scientific method is still limited by human
  imperfection

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How to learn chemistry

• Reading, vocabulary, memorization are only a
  start
• Should be considered a minor part of your
  learning process in chemistry
• Problem solving skills are even more important!
• Why practice homework problems are assigned
• Struggle with them, use answers carefully
• Mistakes can be valuable

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Chapter 2 Scientific Notation
Chemistry 1020 Interpretive chemistry Andy
Aspaas, Instructor
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Types of observations

• Observations are a key part of any type of
  scientific research
• Qualitative a description (a white solid was
  formed)
• Quantitative a specific measurement (the product
  weighs 1.43 grams)

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Measurements and numbers

• Measurements must contain both a number and a
  unit - without both, the measurement is
  meaningless
• Many numbers in measurements are very large or
  very small
• Distance from earth to sun 93,000,000 miles
• Width of an oxygen atom 0.00000000013 meters
• Is there an easier way to deal with such ungainly
  numbers?

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Scientific notation

• Used to make very large or very small numbers
  more manageable
• Multiply a number between 1 and 10 by any power
  of 10
• 200 in scientific notation?
• For even larger numbers, count the number of
  places the decimal point must move, and make that
  the power of 10
• 230,000,000,000 in scientific notation?

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Scientific notation

• Works with small numbers too
• For small numbers, move the decimal point to the
  right, and use that as the negative power of 10
• Left is positive, LIP
• Using a calculator
• The E or EE button on your scientific calculator

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Units of measurement

• Unit which scale or standard is used for a
  particular measurement
• English system US residents are most familiar
  with
• Metric system used in most of the rest of the
  world
• SI, or International System, used in scientific
  work
• Based on metric system
• Agreed upon by scientists worldwide

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Some fundamental SI units

• Quantity Name of unit Abbreviation
• mass kilogram kg
• length meter m
• time second s
• temperature kelvin K
• Most other SI units can be derived from these

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Prefixes to SI units

• Prefix Symbol Meaning Power of 10
• mega M 1,000,000 106
• kilo k 1000 103
• deci d 0.1 10-1
• milli m 0.001 10-3
• micro µ 0.000001 10-6
• nano n 0.000000001 10-9

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Length

• Fundamental SI unit for length meter
• A little longer than a yard
• Using prefixes as the power of 10
• 1 mm 10-3 m 0.001 m
• 1 inch 2.54 cm
• Measured with a ruler or caliper

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Volume

• Amount of 3-dimensional space occupied by an
  object
• Unit liter (L)
• 1 L 1 dm3 (cubic decimeter)
• 1 millileter (mL) 1 cm3
• Commonly used volume unit in chemistry
• Volume measurements
• Graduated cylinder
• Syringe
• Buret

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Mass

• The specific amount of matter present in an
  object
• Measured on a balance
• Not to be confused with weight
• (Force of gravity acting on the mass of an
  object)
• Dependent on the strength of gravity
• Earth vs. moon?
• Measured on a scale
• Mass used much more commonly in chemistry
• SI fundamental unit kilogram

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Uncertainty in measurement

• Analog measurements - measured mechanically
  against some type of physical scale
• Estimate required for last digit of measurement
• Last digit the uncertain digit
• Can be expressed as amount of the uncertain
  digit (4.542 0.001)
• Digital measurements - read from a display
• Last digit still uncertain even though you dont
  do an estimation

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Accuracy vs. Precision

• Accuracy how close a single measurement or set
  of measurements are to their true value
• Precision how similar a number of measurements
  are
• Dartboard example
• Beaker of water example

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Significant figures

• Sum of all certain numbers in a measurement plus
  the first uncertain number
• Indicates the amount of precision with which a
  measurement can be made
• Since each measurement contains uncertainty, that
  uncertainty must be tracked when manipulating the
  measurements

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How many sig figs does a measurement have?

• Nonzero integers are always significant (1 thru
  9)
• Leading zeroes (on the left) are never
  significant
• Captive zeroes are always significant
• Trailing zeroes (at the end) are only significant
  if theres a decimal point
• Exact numbers (obtained by counting) have an
  infinite number of sig figs

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Rounding off

• Calculators dont understand sig figs
• Will return as many digits to you as possible
• You must round the answer to the correct number
  of sig figs
• Look at the digit to the right of the last sig
  fig
• 0-4, just drop it and everything to the right
• 5-9, increase last sig fig by one, drop rest
• Look only at the one digit to the right of the
  last sig fig, ignore all others!

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Determining sig figs in calculations

• When multiplying or dividing, find the
  measurement with the smallest number of sig figs
• Answer must be rounded to that many sig figs
• When adding or subtracting, find the measurement
  with the smallest number of decimal places
• Answer must be rounded to that many decimal
  places
• Practice!

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Dimensional analysis introduction

• We do this all the time without even thinking
  about it
• Example planning a party
• 15 guests
• 3 drinks per guest
• How many drinks should you buy?
• Conversion factor a ratio of two measurements
  with different units that are equal to each other
• Expressed as a fraction, two possible orders!

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Dimensional analysis calculations

• Set up an equation like this
• Known quantity x conversion factor unknown
  quantity
• Orient conversion factor so units of known
  quantity are cancelled
• Multiply the known by the conversion factor
• The only remaining unit should be the one youre
  solving for
• Correct for sig figs
• Does the answer make sense?
• Practice, practice, practice, practice, practice!

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Temperature scales

• Fahrenheit scale used in the US
• Celsius scale used in most rest of world, and by
  most scientists
• Kelvin scale SI base unit of temperature
• 0 K is lowest possible theoretical temperature

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Temperature scales
Fahrenheit Celsius Kelvin
Absolute zero -460 F -273 C 0 K
Water freezes 32 F 0 C 273 K
Body temp 98.6 F 37 C 310 K
Water boils 212 F 100 C 373 K
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Temperature conversions

• Celsius to Kelvin
• Temperature units are the same size
• Zero points are different
• TK TC 273
• Kelvin to Celsius
• Solve above for TC
• TC TK - 273

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Fahrenheit and Celsius

• Different degree units and zero points
• TF 1.80(TC) 32
• TC (TF - 32) / 1.80

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Density

• Density amount of matter present in a given
  volume of substance
• Density mass / volume
• Units could be kg/L, g/cm3, g/mL, etc.