CHEM 213

1. CHEM 213 Organic Laboratory

2. CHEM 213 – Organic Lab Important Information: Recitation: All students will attend mandatory lab recitation on Mondays 3:35 PM. Recitation will NOT meet every week, see attached schedule for recitation dates.

3. Laboratory Schedule * NOTE: Lab recitation will only meet on these Mondays.

4. Required Materials: • Text: Techniques in Organic Chemistry, 2nd edition Jerry R. Mohrig et al, W. H. Freeman and Company, 2006 • Handouts: Downloaded from instructor’s 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 @ https://downloads.its.psu.edu/

5. 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.

6. 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 (<60%).

7. 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 student’s 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 Behrend’s 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.

8. WELCOME to CHEM 213

9. 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)

10. solvent solid 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%20Arman%20Virtual%20Lab/Recrystallization/Recrystallization3.html

11. http://bioweb.wku.edu/courses/Biol220CAR/2ChemBond/waterFig.htmlhttp://bioweb.wku.edu/courses/Biol220CAR/2ChemBond/waterFig.html 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

12. Recrystallization Solvents www.chem.umd.edu/organiclabs/Chem232/01Recrystallization/Lab01.ppt

13. 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

14. 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

15. 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

16. Hot Plate Hot Filtration

17. http://wulfenite.fandm.edu/labtech/crystals.htm 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

18. to vacuum Step 6 • collect crystals • vacuum filtration using Buchner Funnel

19. 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%20Arman%20Virtual%20Lab/Recrystallization/recrystallization1.mov

20. amount of solid recovered % = X 100 amount of initial solid Percent Recovery • evaluates recrystallization quantitatively • do not forget to record weight of unknown • not the same as a percent yield

21. A. Sublimation B. Melting C. Evaporation Melting Points • temperature where solid & liquid phases in equilibrium • characteristic physical property of solid • the identityof an organic solid • the purity of an organic solid • most organic solids melt 25 - 250 oC

22. 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

23. Melting Points Consider the effects of intermolecular forces on the melting point of three organic compounds of similar mass:

24. Hydrogen Bonding Benzoic acid melting point 122-3 oC

25. 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.

26. 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.

27. 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

28. 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

29. Impure Solid cyclohexane contaminated naphthalene, mp 62-69oC

30. 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?

31. MP Pure A MP Pure B Temp (◦C) 100% A 100% B Mole % Composition 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

32. 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

33. 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

34. 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

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

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

37. 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

38. Questions? Comments?