Chemistry: The Central Science

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Chemistry The Central Science

• Chemistry is the study of matter and all of the
  changes that can happen to it. For that reason it
  is central to our understanding of how the world
  works, even if it may not be the most basic of
  the sciences

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Matter Anything occupying space and having
mass.
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Mass vs. Weight

• Mass, measured in grams in chemistry, kilograms
  in physics, is the measure of how hard it is to
  get an object moving. It is independent of where
  the object is.
• Weight is the pull of gravity on an object. If
  the gravity is of a different value, then the
  weight will change, though the mass will not.

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Composition of matter

• Smallest piece of a specific type of matter is
  the atom. It is very small, approximately
  .00000002 cm
• Atoms are subdivided into smaller particles,
  protons, neutrons, and electrons. The number and
  arrangement of these particles determine much of
  how individual atoms behave physically and
  chemically.

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Classes of Matter

• Elementscomposed of only one type of atom, can
  be two or more linked together, like oxygen, O2
• Compoundscombinations of two or more different
  elements by chemical linkages called bonds, in
  specific set proportions for each -- examples
  salt, sugar, quartz, carbon dioxide, water
• Mixturescombination of two or more substances in
  varying proportions of eachlumping together of
  stuffs, examplesrocks, concrete, milk, soda,
  air

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Names and Symbols of Elements

• Elements have gotten their names over history
  from the people who discovered and used them
• The symbols of the elements are taken from the
  accepted international name for the element,
  which may be from English, Latin, or German
• Memorize the symbols of elements 1-40, 42, 43,
  46-56, 74, 78-84, 86-94 QUIZ tomorrow!!!

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Types of Mixtures

• Mixtures have variable composition.
• A homogeneous mixture is a solution (for
  example, vinegar)
• A heterogeneous mixture is, to the naked eye,
  clearly not uniform (for example, a bottle of
  ranch dressing)

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Pure Substances

• Can be isolated by separation methods
• -? Chromatography
• - Filtration
• - Distillation

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Separation Techniques

• Filtration-- separating a solid from a liquid
  using gravity or vacuum
• Distillation--using boiling point differences to
  separate a liquid from something dissolved in it
• Crystallizationusing differences in dissolving
  power of a substance in another substance to make
  one part of a mixture become pure crystals
• Chromatography--using differences in dissolving
  ability to separate portions of a mixture

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Homework 1-3a

• p. 9 -- 6, 7, 9, 10
• p. 69 15, 17, 19
• p. 7725
• p. 82ff47, 49, 53, 56

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Properties of Matter

• Properties include the characteristics and
  behavior of matter. Pure substances (elements
  and compounds) have fixed properties, mixtures do
  not.
• Physical properties can be measured without
  changing the substance. These can depend on how
  much is there (extensive), such as mass or can
  be independent of amount(intensive), such as
  density or temperature.
• Chemical properties can only be found in
  reactions which rearrange the atoms of substances

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States of Matter

• Four States of Matter
• Solid rigid - fixed volume and shape
• Liquid definite volume but assumes the shape
  of its container
• Gas no fixed volume or shape - assumes the
  shape of its container
• Plasma ionized gas atoms in stars or welders

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Changes in Matter

• Physical changes only change the appearance of a
  substance without changing its propertiesbreaking
  , melting, boiling, freezing are examples
• Chemical changes cause rearrangement of the atoms
  within the substance, making new properties in
  chemical reactions. However, the change does not
  destroy or make any new matter, which is the Law
  of Conservation of Mass.

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Homework 1-3b

• p. 602, 5
• p. 6510, 11, 14
• p. 82ff34, 36, 37, 39, 44

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Nature of Measurement

• Measurement - quantitative observation
  consisting of 2 parts
• Part 1 - number
• Part 2 - scale (unit)
• Examples
• 20 grams
• 6.63 ? ????? Joule seconds

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International System(le Système International)

• Also called the SI system, it is based the on
  metric system and units derived from metric
  system.
• Two types of units are base units and derived
  units.

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The Fundamental SI Base Units
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Units
Base units are defined by fixed properties or
objects. The meter was once defined as a portion
of the distance from poles to equator, the
kilogram by the mass of an object in a Paris
museum. Derived units are combinations of base
units by applying mathematical operations between
them, such as volume (length cubed) or speed
(length divided by time)
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Uncertainty in Measurement

• A digit that must be estimated is called
  uncertain. A measurement always has some degree
  of uncertainty.

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Precision and Accuracy

• Accuracy refers to the agreement of a particular
  value with the true value.
• Precision refers to the degree of agreement
  among several elements of the same quantity.

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Types of Error

• Random Error (Indeterminate Error) - measurement
  has an equal probability of being high or low.
• Systematic Error (Determinate Error) - Occurs in
  the same direction each time (high or low), often
  resulting from poor technique.

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Rules for Counting Significant Figures - Overview

• 1. Nonzero integers
• 2. Zeros
• - leading zeros
• - captive zeros
• - trailing zeros
• 3. Exact numbers

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Rules for Counting Significant Figures - Details

• Nonzero integers always count as significant
  figures.
• 3456 has
• 4 sig figs.

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Rules for Counting Significant Figures - Details

• Zeros
• - Leading zeros do not count as
• significant figures.
• 0.0486 has
• 3 sig figs.

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Rules for Counting Significant Figures - Details

• Zeros
• - Captive zeros always count as
• significant figures.
• 16.07 has
• 4 sig figs.

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Rules for Counting Significant Figures - Details

• Zeros
• -? Trailing zeros are significant only
• if the number contains a decimal point.
• 9.300 has
• 4 sig figs.

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Rules for Counting Significant Figures - Details

• Exact numbers have an infinite number of
  significant figures.
• 1 inch 2.54 cm, exactly

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Rules for Significant Figures in Mathematical
Operations

• Multiplication and Division sig figs in the
  result equals the number in the least precise
  measurement used in the calculation.
• 6.38 ? 2.0
• 12.76 ? 13 (2 sig figs)

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Rules for Significant Figures in Mathematical
Operations

• Addition and Subtraction sig figs in the
  result equals the number of decimal places in the
  least precise measurement.
• 6.8 11.934
• 18.734 ? 18.7 (3 sig figs)

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Length, Mass, Volume

• Length in the metric system is based on the meter
  and subdivided by powers of ten using prefixes
• Mass in chemistry is based on the gram,
  subdivided in the same way
• Volume is measured with a unit called the liter,
  which is equal to 1000 cm3 or 1000 mL
• The dimensional analysis method is used to
  convert between metric units or between metric
  and non-metric units, such as miles or quarts or
  pounds

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Dimensional Analysis

• Use of Unit Factors makes conversions between
  units much easier

157 mm 10-3 m 1 mm 1.57 x 105 m
m 1 mm 10-6 m 5.38 yr
365.25 da 24 hr 60 min 2.83 x 106
min 1 yr 1 da
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Dimensional Analysis

• Use of Unit Factors makes conversions between
  units much easier

157 mm 10-3 m 1 mm 1.57 x 105 m
m 1 mm 10-6 m 5.38 yr
365.25 da 24 hr 60 min 2.83 x 106
min 1 yr 1 da
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Unit Analysis Problem

• How many days are in 2.5 years?
• Step 1 We want days.
• Step 2 We write down the given 2.5 years.
• Step 3 We apply a unit factor (1 year 365
  days) and round to two significant figures.

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Another Unit Analysis Problem

• A can of Coca-Cola contains 12 fluid ounces.
  What is the volume in quarts (1 qt 32 fl oz)?
• Step 1 We want quarts.
• Step 2 We write down the given 12 fl oz.
• Step 3 We apply a unit factor (1 qt 32 fl oz)
  and round to two significant figures.

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Another Unit Analysis Problem

• A marathon is 26.2 miles. What is the distance
  in yards (1 mi 1760 yards)?
• Step 1 We want yards.
• Step 2 We write down the given 26.2 miles.
• Step 3 We apply a unit factor (1 mi 1760
  yards) and round to three significant figures.

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Metric-Metric Conversion Problem

• What is the mass in grams of a 325 mg aspirin
  tablet?
• Step 1 We want grams.
• Step 2 We write down the given 325 mg.
• Step 3 We apply a unit factor (1 mg 0.001 g)
  and round to three significant figures.

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Two Metric-Metric Conversions

• A hospital has 125 deciliter bags of blood
  plasma. What is the volume in milliliters?
• Step 1 we want the answer in mL
• Step 2 we have 125 dL.
• Step 3 we need to first convert dL to L and then
  convert L to mL
• 0.1 L and 1 mL
• 1 dL 0.001 L .

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Problem Continued

• Apply both unit factors, and round the answer to
  3 significant digits.
• Notice that both dL and L units cancel, leaving
  us with units of mL.

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Another Example

• The mass of the Earth is 5.98 1024 kg. What is
  the mass expressed in megagrams, Mg?
• We want Mg we have 5.98 1024 kg
• Convert kilograms to grams, and then grams to
  megagrams.

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English-Metric Conversion

• A half gallon carton contains 64.0 fl oz of milk.
  How many milliliters of milk are in a carton?
• We want mL, we have 64.0 fl oz.
• Use 1 qt 32 fl oz, and 1 qt 946 mL.

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Compound Unit Problem

• A Corvette is traveling at 95 km/hour. What is
  the speed in meters per second?
• We have km/h, we want m/s.
• Use 1 km 1000 m and 1 h 3600 s.

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Conclusions Continued

• A Volkswagen Beetle engine displaces a volume of
  498 cm3 in each cylinder. What is the
  displacement in cubic inches, in3?
• We want in3, we have 498 cm3.
• Use 1 in 2.54 cm three times.

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Temperature

• Celsius scale ??C
• Kelvin scale K
• Fahrenheit scale ??F

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Temperature
Conversions are not done by dimensional analysis
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Density

• Density is the mass of substance per unit
• volume of the substance

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Home/Class work

• p30 5, 7
• p42 39, 42
• p50ff 72, 73, 74, 80, 84, 93
• Complete ONE paper per lab group