Experiment 1:

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Experiment 1

• STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY

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OBJECTIVES

• To learn how to identify which intermolecular
  forces exist between organic compounds.
• To investigate the relationship between
  structure, intermolecular forces and solubility
  using solubility testing.

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ROLE OF INTER- AND INTRAMOLECULAR FORCES

• Physical state
• solid, liquid gas
• Distillation
• difference in BP
• Extraction
• difference in solubility
• Chromatography
• different IMF between analyte and stationary vs.
  mobile phase
• Biology
• secondary structure of proteins
• DNA and DNA-RNA base pairing

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TYPES OF INTERMOLECULAR FORCES

• London Dispersion Forces
• Dipole-Dipole Forces
• Hydrogen Bonding
• Acceptors
• Donors
• Ion-dipole Forces

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LONDON DISPERSION FORCES

• The London dispersion force is the weakest
  intermolecular force.
• It is a temporary attractive force that results
  when the electrons in two neighboring atoms
  occupy positions that make the atoms form
  temporary dipoles.
• Since electrons are constantly in motion, they
  can be distributed unevenly about the nucleus.
  This results in the formation of a temporary
  dipole.
• A second atom or molecule, in turn, can be
  distorted by the appearance of the dipole in the
  first atom or molecule (because electrons repel
  one another) which leads to an electrostatic
  attraction between the two atoms or molecules.

d
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LONDON DISPERSION FORCES

• Dispersion forces are present between all
  molecules, whether they are polar or nonpolar.
• Larger and heavier atoms and molecules exhibit
  stronger dispersion forces than smaller and
  lighter ones.
• Compounds which contain carbons and hydrogens
  ONLY possess LDF ONLY.

LESS LDF
MORE LDF
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DIPOLE - DIPOLE FORCES

• Dipole moment (m) Electrostatic attraction
  between polar molecules.
• It is a measure of the unevenness of electron
  density in a bond or molecule.
• It depends on both electronegativity of atoms and
  on molecular geometry.

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DIPOLE - DIPOLE FORCES

• Dipole-dipole forces are present only in polar
  molecules.
• They occur when the d end of one polar molecule
  is attracted to the d- end of another.

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HYDROGEN BONDING

• Hydrogen bonds are a result of the large
  difference in electronegativity between H and N,
  O, or F.
• They occur when the H of one molecule attached to
  an O or N is attracted to an O or N of a
  different molecule.
• Some compounds have a H to donate to hydrogen
  bonding, while others can only accept a H from
  other compounds to form hydrogen bonds.

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HYDROGEN BONDING
Notice that compounds containing an O or N
with a H DIRECTLY bound to it are donors and
acceptors!
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ION-DIPOLE

• An ion-dipole force exists between an ion and the
  partial charge on the end of a polar molecule.
• They are especially important for solutions of
  ionic substances in polar solvents, such as NaCl
  in water.

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EXPERIMENTAL OUTLINE

• A Test solubility of compounds in hexane and
  water.
• B Test solubility of organic liquids in water.
• C Test solubility of alcohols in hexane and
  water.
• D Test solubility of organic solids in diethyl
  ether, water, acidic and basic solutions.

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Table 1.1

Organic Liquid Structure Intermolecular Force(s) (list all present) Miscibility in hexane Miscibility in water
hexane London dispersion M I
toluene
diethyl ether
ethyl acetate
1-butanol
methanol
water M
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Tables 1.2 and 1.3
Solute Structures Intermolecular Force(s) drops miscible in 1 mL of water
toluene 1
ethyl acetate 2
1-butanol 4
Alcohol Structure Boiling Point (Co) Miscibility in hexane Miscibility in water
methanol 64.7
ethanol 78.5
1-propanol 97.0
1-butanol 117.7
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Acid-Base Chemistry
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Table 1.4
Organic Solid Mol. Formula Mol. Weight Melting point Hazards Structure Intermolecular Force(s)   Solubilities   Solubilities   Solubilities   Solubilities
Organic Solid Mol. Formula Mol. Weight Melting point Hazards Structure Intermolecular Force(s) diethyl ether water 10 NaHCO3 1M HCl
benzoic acid C7H6O2 122.12 g/mol 122-123 oC Harmful if swallowed Eye irritant
sodium benzoate C7H5NaO2 144.10 g/mol gt300 oC Avoid contact with skin and eyes
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IMF FLOW CHART
Interacting molecules or ions
YES
NO
NO
NO
Are ions involved?
Are polar molecules and ions both present?
Are polar molecules involved?
YES
DIPOLE-DIPOLE Ex CH3Cl
YES
NO
YES
Are hydrogen atoms bonded to N, O, or F atoms?
IONIC BONDING Ex NaCl
LDF ONLY Ex CH3CH3
ION-DIPOLE Ex NaCl in H2O
NO
YES
HYDROGEN BOND Acceptor Ex CH3OCH3
HYDROGEN BOND Donor Ex H2O, NH3
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SAFETY CONCERNS

• All solvents used in todays lab are volatile.
  Wear safety goggles at all times, and use fume
  hoods.

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WASTE DISPOSAL

• Pour all liquid waste from this experiment into
  the container labeled LIQUID ORGANIC WASTE.
• Do NOT pour any waste down the drain!

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LABORATORY NOTEBOOK(Pre-lab)

• OBJECTIVE (Must clearly state)
• What you will evaluate
• How you will evaluate it
• TABLE OF PHYSICAL DATA (Single organized table,
  must include...)
• LIQUIDS (MW, bp, density, hazards) hexane,
  toluene, diethyl ether, ethyl acetate, acetone,
  butanol, propanol, ethanol, methanol, and
  hydrochloric acid.
• SOLIDS (MW, mp, hazards) sodium benzoate, sodium
  bicarbonate, and benzoic acid.
• REFERENCE TO PROCEDURE (Must include)
• Full title
• Edition
• Authors
• page numbers where actual procedure can be found

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LABORATORY NOTEBOOK(In-lab)

• DATA/CALCULATIONS
• Not applicable for this experiment. All
  observations will be recorded directly onto the
  Final Lab Report.
• EXPERIMENTAL PROCEDURE
• In paragraph form, briefly describe the procedure
  that you actually followed during the lab.
• Paragraph must be written in PAST TENSE, PASSIVE
  VOICE.
• Include any mistakes, accidents or observations
  if necessary.

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FOR NEXT LAB

• Experiment 1 Final Lab Report due.
• Experiment 2 Pre-lab Notebook entry due.
• It is highly recommended that you watch the
  following video prior to coming to lab.
• http//www.youtube.com/watch?v3JlIPnyrZMw