CHEM 213

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CHEM 213

• Organic Laboratory

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CHEM 213 Organic Lab
Important Information
Recitation All students will attend mandatory
lab recitation on Mondays 335 PM. Recitation
will NOT meet every week, see attached schedule
for recitation dates.
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Laboratory Schedule
NOTE Lab recitation will only meet on these
Mondays.
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Required Materials

• Text Techniques in Organic Chemistry, 2nd
  edition
• Jerry R. Mohrig et al, W. H. Freeman and
  Company, 2006
• Handouts Downloaded from instructors web site
  prior to recitation
• for each new experiment
• Notebook A bound notebook is required
• unacceptable - spiral or three-ring bound
  notebooks
• most convenient - composition notebook
• Goggles Any goggles or safety glasses with
  side-shields
• Software ChemDraw _at_ https//downloads.its.psu.edu
  /

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Assignments

• Notebook (35 pts)
• PreLab
• Quizzes (50 pts)
• recitation includes a short (10 pt) quiz on the
  readings
• six quizzes - no make-up quizzes but one quiz
  may be dropped
• Lab Reports (275 pts)
• First 3 experiments a short report (25 pts each),
  emphasizing a particular section
• Final 4 experiments require a full report (50 pts
  each)
• Late reports will be penalized at two points per
  day up until they are one week late when they
  will not longer be accepted.
• Final Exam (75 pts)
• A comprehensive final exam will be given during
  the recitation. (see schedule)
• General Lab Courtesy
• Failure to collaborate, cooperate and abide by
  the safety rules will result in an automatic
  deduction of points from that lab, at the
  discretion of the instructor. Students who do not
  checkout their desk equipment will be charged a
  25 checkout fee.

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Grades
The minimum grade you will receive A (100-93),
A- (92-90 ), B (89-87), B (86-83), B-
(82-80), C(79-75), C (74-70), D (69-60), F
(lt60).
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Notes

• Academic Integrity It is expected that each
  student will do his/her own work on all
  assignments including quizzes and laboratory
  reports.
• This includes but is not limited to
• stealing, purchasing or copying quizzes and/or
  laboratory reports from present or previous
  students.
• even the possession of other students notebook,
  laboratory reports, or quizzes constitutes a
  violation of the academic integrity polity at
  Penn State.
• For more information see the Academic Integrity
  Academic Dishonesty (Senate Policy 49-20) at
  http//www.psu.edu/ufs/policies/ or Behrends
  Academic Integrity policy at http//www.pserie.psu
  .edu/faculty/academics/integrity.htm.
• Students with disabilities If you have a
  disability-related need for modifications or
  reasonable accommodations in this course, contact
  the Disability Specialist in the Office of
  Student Affairs, Room 115 Reed Union Building,
  898-6111.

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WELCOME to CHEM 213
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Purification of Organic Solids Identification
using Melting Point Determination Experiment 1
Experimental Objectives

• become familiar with common heating cooling
  methods (Technique 6)
• purify organic unknown using recrystallization
  (Technique 9)
• identify unknown by melting point solubility
  data (Technique 10)

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Recrystallization

• crystalline material (solute) is dissolved in a
  hot solvent then returns to solid when cooled
• important to understand dissolving

• choice amount of solvent is critical

http//server1.fandm.edu/departments/chemistry/Van
20Arman20Virtual20Lab/Recrystallization/Recryst
allization3.html
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Solubility

• solvent temperature - solubility increases with
  temperature
• solvent volume - amount of solute vs. volume of
  solvent
• solvent properties - solute/solvent interactions
  like dissolves like
• - polar H2O dissolves most (polar) inorganic
  compounds
• - nonpolar organic solvents dissolve most
  (nonpolar) organics

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Recrystallization Solvents
www.chem.umd.edu/organiclabs/Chem232/01Recrystalli
zation/Lab01.ppt
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7 Steps to Recrystallization

• find best solvent
• dissolve bulk sample in solvent
• decolorize (if necessary)
• remove insoluble impurities (if necessary)
• cool solute/solvent mixture
• collect crystals
• dry analyze crystals

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Step 1

• find best solvent
• small (test tube) size using a sand bath
• dissolves went hot not when cold
• limited to six initial solvent choices
• water
• ethanol
• ethyl acetate
• methylene chloride (dichloromethane)
• toluene
• hexane

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Steps 2 - 4

• dissolve bulk sample in solvent
• minimum amount of solvent to dissolved solute
  with heat
• this will be unique to solute solvent choice
• use boiling chips or sticks
• decolorize (if necessary)
• charcoal adheres to colored impurities
• remove insoluble impurities (if necessary)
• hot gravity filtration

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Hot Filtration
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Step 5

• cool solute/solvent mixture
• cool slowly to eliminate soluble impurities from
  crystallizing
• If crystals do not form try
• scratching with glass stir rod
• add a seed crystal
• evaporate some excess solvent

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Step 6

• collect crystals
• vacuum filtration using Buchner Funnel

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Step 7

• dry
• leave on vacuum filter
• leave crystals in funnel open in desk
• heat under a heat lamp take care
• Review Steps 2 6 video

http//server1.fandm.edu/departments/chemistry/Van
20Arman20Virtual20Lab/Recrystallization/recryst
allization1.mov
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Percent Recovery

• evaluates recrystallization quantitatively
• do not forget to record weight of unknown
• not the same as a percent yield

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Melting Points

• temperature where solid liquid phases in
  equilibrium
• characteristic physical property of solid
• the identity of an organic solid
• the purity of an organic solid
• most organic solids melt 25 - 250 oC

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Melting Points

• Organic molecules within the solid are held
  together
• by intermolecular forces
• Hydrogen bonding 2 10 kcal/mol
• Dipole-dipole interactions 0.5 - 2 kcal/mol
• Van Der Waals forces (temporary dipole)
  0.5 kcal/mol
• compare to a intramolecular covalent bond 100
  kcal/mol

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Melting Points

• Consider the effects of intermolecular forces on
  the melting point of three organic compounds of
  similar mass

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Hydrogen Bonding
Benzoic acid melting point 122-3 oC
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Dipole-Dipole
Ethyl benzoate, melting point -23 oC
Dipole-dipole interactions are weaker. Ethyl
benzoate is heavier than benzoic acid, yet its
melting point is below room temperature, almost
150o below benzoic acid.
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Van Der Waals
Ethyl benzene, melting Point -95 oC
Temporary dipoles are the weakest form of
intermolecular force. Solids held together by
these forces have low melting points.
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Melting Point Determination

• The energy (heat) required to break these
  intermolecular interactions is the same for any
  two molecules within the solid
• pure organic compounds have a distinct melting
  point that can be used for identification
• melting point should also occur over a very
  narrow range of temperatures
• impurity in the solid disrupts intermolecular
  forces takes less energy to melt solid
  therefore lowering and broadening melting point
  range

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Pure Solid
The Van Der Waals forces that hold the solid
together are regular are the same from molecule
to molecule Pure naphthalene melts at 82-83oC
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Impure Solid
cyclohexane contaminated naphthalene, mp 62-69oC
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Melting Point Determination
Problem Suppose you are cleaning the chemical
stockroom and you encounter a reagent bottle
whose label has decomposed. You suspect that the
compound could be either benzoic acid (mp 122-123
oC) or succinimide (mp 123-5 oC). You take a
melting point, and sure enough the unknown melts
at 123 oC. How would you use what you have
learned to determine the true identity of the
contents of the bottle?
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Mixed Melting Point

• Solution
• obtain known samples of benzoic acid
  succinimide
• mix each of the known samples with a portion of
  the unknown
• determine the melting point for each mixed sample

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Thomas-Hoover

• silicone oil bath
• five samples simultaneously
• oil slow to respond to temperature changes so a
  slower, better melting point can be obtained
• silicone oil has a temp limit 200 C
• good choice for organics that melt between 20-200
  C

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Mel-Temp

• uses a heated aluminum block
• three samples simultaneously
• aluminum is quick to respond to temperature
  changes higher temps can be achieved more
  quickly
• advantage in determining high melting points
• good choice for organics that melt over 200 C

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MP Sample Size
Use the minimum amount of sample slowest
heating rate to obtain the sharpest, most
accurate melting point.
Sample size samples placed in a mp capillary
tube. Use the minimum amount seen through the
magnifier (1-2 mm)
Heating Rate quickly go to 20 C below the
expected MP, then slow to 1-2 C per minute to
observe the correct MP
Melting Point Video
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Introduction

• Brief Paragraph (2-5 sentences)
• interesting background information
• goals/objective
• reaction (if applicable)
• proper reference
• Do not include
• explanation
• procedure

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Conclusion

• Brief Paragraph (2-3 sentences)
• statement summarizing discussion
• must include conclusion
• Typed, 12 point black font, double spaced
• grammar, spelling, etc.

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Notebook

• Chapter 3 in Mohrig
• table of contents (leave room)
• numbered pages (no pages torn out)
• Prelab
• title, date
• purpose including balanced reaction (if
  applicable)
• chemical data table
• do not write out the procedure (outline if
  helpful)
• Observations
• in class notes recorded in ink
• calculations

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Questions?

• Comments?