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Experiment 1:

Experiment 1:. STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY. 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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Experiment 1:

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  1. Experiment 1: STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY

  2. 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.

  3. 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

  4. TYPES OF INTERMOLECULAR FORCES • London Dispersion Forces • Dipole-Dipole Forces • Hydrogen Bonding • Acceptors • Donors • Ion-dipole Forces

  5. d - -------------- d - d + 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 +

  6. 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

  7. 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 electronegativityof atoms and on molecular geometry.

  8. 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.

  9. 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.

  10. HYDROGEN BONDING *** Notice that compounds containing an O or N with a H DIRECTLY bound to it are donors and acceptors!***

  11. 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.

  12. 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.

  13. Table 1.1

  14. Tables 1.2 and 1.3

  15. Acid-Base Chemistry

  16. Table 1.4

  17. IMF FLOW CHART Interacting molecules or ions NO NO YES NO Are polar molecules involved? Are ions involved? Are polar molecules and ions both present? 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

  18. SAFETY CONCERNS • All solvents used in today’s lab are volatile. Wear safety goggles at all times, and use fume hoods.

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

  20. 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

  21. 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.

  22. FOR NEXT LAB… • Experiment 1Final Lab Report due. • Experiment 2Pre-lab Notebook entry due. • It is *highly recommended* that you watch the following video prior to coming to lab. • http://www.youtube.com/watch?v=3JlIPnyrZMw

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