EVEN Hypothesis - Reacting to the Past

Report
Chemistry at Karlsruhe 1860:
Using Reacting to the Past in
General Chemistry
David E. Henderson
Trinity College
Susan K Henderson
Quinnipiac University
Philosophies of Science
• Plato –describe nature by thinking about the ideal state
rather then the real state (logic)
• Aristotle –observe nature and then try to describe its
properties and behavior
• Empiricists –develop laws and relationships to describe
nature only by direct observations/measurements.
– Not concerned with underlying causes.
• Realists – Understanding underlying causes is necessary
to fully explain observations
– atoms must be considered to be real to fully describe how
different arrangements of the same atoms can produce different
properties.
Learning Goals – Karlsruhe Game
• History of the study of matter and its behavior
referred to as “chemistry”
• Evidence as the basis of chemical knowledge
• The process of science
• Development of quantitative skills
Karlsruhe Conference
• First International Scientific Meeting
– held in Karlsruhe, Germany, October 1860
• Topics to be considered
– Are Atoms Real?
– What is the proper formula for water? HO, H2O
– Can we assign atomic weights to elements or only
equivalent weights?
• Is Carbon 6 or 12? Oxygen 8 or 16?
Dalton’s Atomic Theory (1808)
• Each element is made up of tiny particles
called atoms.
Dalton’s Atomic Theory (continued)
• The atoms of a given element are
identical; the atoms of different
elements are different in some
fundamental way or ways.
Dalton’s Atomic Theory (continued)
• Chemical compounds are formed when
atoms of different elements combine
with each other. A given compound
always has the same relative numbers
and types of atoms.
Dalton’s Atomic Theory (continued)
• Chemical reactions involve
reorganization of the atoms—changes in
the way they are bound together.
• The atoms themselves are not changed
in a chemical reaction.
Laws from Dalton’s Theory
Law of conservation of mass
– Mass is neither created nor destroyed
Law of definite proportion
– A given compound always contains exactly the
same proportion of elements by mass.
Law of multiple proportions
–
If two elements can combine to form more than one
compound, the masses of one element that combines
with a fixed mass of the other element are in ratios of
small whole numbers
CuO and Cu2O
Fe 2O3 and FeO
Karlsruhe Conference
• Factions
– Berzelian Empiricists (Bunsen, Frankland)
– Liebig Empiricists (Liebig, Meyer)
– Organic Realists (Williamson, Kekule)
– Cannazzaro
– Indeterminates (Pasteur, Mendeleev)
Berzelians
• Prof Berzelius was one of the leading chemists
at that time.
• Berzelius performed over 2000 different
experiments
This group assigned relative weights of 1 for H, 6 for
C and 16 for O. Meaning that C is 6 times as heavy
as H, O is 16 times as heavy as H
Berzelians
• They reject anything that is not based on
observation and measurement, ie empirical
data
• They believe that matter is composed of
electropositive and electronegative atoms
Example of empirical data
• Data for the Law of multiple proportions
–
–
–
–
1 g oxygen reacts with 0.4375 g nitrogen
1 g oxygen reacts with 0.8750 g nitrogen
1 g oxygen reacts with 1.750 g nitrogen
Suggests that oxygen reacts with nitrogen to give three
different compounds. Look at the ratios of the mass of
nitrogen that reacts with 1 gram of oxygen
• 0.8750/0.4375= 2
• 1.750/0.4375= 4
• NO, NO2, NO4 or NO1/2, NO, NO2
can’t tell which from this data
Liebig
• Prof. Justus Liebig and his group developed methods to
analyze organic chemical
• Like the Berzelians they dealt only with empirical data and
equivalent weights
• Organic Compounds generally are made up of carbon,
hydrogen and oxygen
• Organic compounds when combusted in air form water, and
carbon dioxide
• Liebig determined the simplest formulas (empirical formulas)
of any compound of C, H and O which includes sugars,
alcohols, and many others.
• Liebig’s apparatus is still honored in the Am Chem Soc Logo
Gay-Lussac and Avogadro (1809—1811)
• Gay—Lussac
 Measured (under same conditions of T and
P) the volumes of gases that reacted with
each other. For Example for water H2O
 But 1 g H combines with 8 g O  9 g water
suggesting HO
 Basic conflict between volume and mass
measurements!
Gay-Lussac and Avogadro (1809—
1811)
•
Avogadro’s Hypothesis
 At the same T and P, equal volumes of
different gases contain the same number of
particles.
 EVEN Hypothesis – Widely Accepted
The EVEN Hypothesis
• Equal Volumes have even numbers
– All gases are observed to follow this rule
• Implication is that all atoms must be the same
size since a filled container of different gases
weigh different amounts
• Therefore - Some atoms are heavier than
others
Rise of Organic Chemistry
• Discovery of isomers
– Same molecule but assembled differently
• Butyl Alcohol and ether both same formula but
different properties
• Butyric acid and hydroxyethylene both C2H2O according
to Liebig
– One an acidic liquid and one a volatile alcohol
– Idea of chemical structure related to properties
• If arrangement of atoms is important, they
must be real
Organic Realists
• Many different organic compounds can have
the same empirical formula but are very
different, sugars are denoted as CH2O but
glucose (blood sugar) and sucrose (table
sugar) are two different substances.
• The EVEN hypothesis is used to determine
relative weights of organic compounds
Canizzaro
• Stanisllao Canizzaro, Prof of Chemistry in
Genoa, Italy
• Not well known
Indeterminates
• Every RTTP Game has indeterminates
• They are assigned roles and may have secrets
but they have no predetermined opinions
about the issues being debated
• In this game they will act as moderators of the
game sessions.
• Their votes are critical to the outcome, so they
are the ones to be convinced
Things All Factions Believe are True
• EVEN – Equal Volumes contain Equal Numbers
– Hypothesis allows determination of relative
weights of different compounds
• Law of Multiple Proportions
– Compounds contain fixed ratios of elements
– Some elements combine in multiple ratios
Things All Factions Don’t Know
•
•
•
•
•
•
•
•
The Mole Concept
Atomic Weights (Relative and Equivalent only)
The Periodic Table
Diatomic Nature of Elemental Gases, O2, H2
Whether Atoms are Real or just a useful idea
Relative weights of Carbon and Oxygen
Formulas of water and carbon oxides
Concept of Covalent Bonding
Data for the Debate
• Experimental data to be presented
– Combination of Metals with oxygen (oxidation)
– Combination of Metals with hydrogen (reduction)
– Electrolysis (decomposition)
– Combustion (burn organic molecule to decompose
into Carbon, Hydrogen and Oxygen
– Gas Density measurements allowed the relative
weights of atoms and molecules to be determined
Game Session 1
• Factions describe experiments
• Factions present calculated results and
conclusions from the data
• Each faction makes different assumptions
– Assumptions are based on empirical evidence
• Answer keys for are provided for this
workshop
Game Session 2
• Examine the other groups data using your
assumptions
• Look for consistent results
• Make arguments for your faction’s objectives

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