WWU -- Chemistry Chemistry 354 Organic Chemistry Laboratory I

WWU -- Chemistry Safety The organic chemistry safety presentation on the web is available on the web at the following address: Read pp 542 – 558 in the lab book. We administer the safety quiz online at the following URL: A link to the safety quiz is included at the bottom of the instruction page. You will have 30 minutes to complete the 25 question quiz.

WWU -- Chemistry Safety First Try: Tuesday, June 20, 8AM to Friday, June 23, 10AM Second Try: Tuesday, June 20, 8:00 AM to Friday, June 23, 10 AM Third Try: Tuesday, June 20, 8:00AM to Friday, June 12, 10 AM In order to be enrolled in this course, each student will be required to take and pass a laboratory safety quiz. You must pass the quiz before Tuesday, April 6th at NOON. If you cannot successfully pass the quiz, you will be dropped from this course.

WWU -- Chemistry Chemistry 354 Lecture Purpose: To ensure that each student, regardless of laboratory section and instructor, receives the same information in preparation for the experiment. Examinations: The midterm and final examinations will be given in this lecture session.

WWU -- Chemistry Introduction to Microscale Laboratory Read: –Experiment 1 (pp. 2 – 13) –Technique 1 (pp. 542 – 558) –Technique 2 (pp. 558 – 565) –Technique 3 (pp. 566 – 573) –Technique 4 (pp. 574 – 580)

WWU -- Chemistry Introduction to Microscale Laboratory Macroscale: Quantities of chemicals on the order of 5 to 100 grams. Glassware containers up to 500 mL. Microscale: Quantities of chemicals on the order of to grams. Glassware containers up to 25 mL.

WWU -- Chemistry Introduction to Microscale Laboratory Heating –No flames Dispensing of liquids Assignment: –Laboratory exercise 1 (parts A and B) –Laboratory exercise 2 There is no pre-lab or laboratory report required for this assignment-

WWU -- Chemistry Experiment 2: Solubility Reading Assignment –Experiment 2 (pp.13 – 20) –Technique 5 (pp. 581 – 589) –Technique 10 (pp. 637 – 646)

WWU -- Chemistry NOTE: You will be expected to submit a pre-lab assignment before you begin this experiment! Consult the syllabus for your laboratory section for the due date for the pre-lab exercise and for the final laboratory report.

WWU -- Chemistry Solubility The extent to which a substance is soluble in a solvent. Examples (solubility in water at 25°C): –Cholesterol mg/mL –Caffeine22 mg/mL –Citric acid620 mg/mL

WWU -- Chemistry Solubility -- Definitions Solute: The substance that is being dissolved Solvent: The medium in which the solute is being dissolved. NOTE: In a solution, the solvent molecules greatly outnumber the solute molecules.

WWU -- Chemistry If a liquid organic compound is dissolved in a solvent… Miscible: solute and solvent mix homogeneously in all proportions Immiscible: solute and solvent do not mix; they form two separate liquid phases

WWU -- Chemistry Part A: Solubility in a Series of Solvents

WWU -- Chemistry Some hints on doing the solubility lab: 1.You can do the various parts of the experiment in any order you wish! This eliminates lineups by the Balances. Part A is especially time consuming! 2.Be sure to approximate the amounts of solids you are using in Part A. You don’t need to be exact on the weights.

WWU -- Chemistry You will study the solubility behavior of benzophenone, malonic acid, and biphenyl in: Water, methanol, hexane How does the polarity of the solute influence the solubility in each of these solvents? What factors are at play, here?

WWU -- Chemistry Make a guess as to the solubility of malonic acid in water. Notice that the acid has two very polar carboxyl groups in the compound. Would you expect this compound to be soluble in the non-polar hexane solvent?

WWU -- Chemistry How consider the solubility of biphenyl in water. Make a guess as to the whether it will be soluble in water. What about the solubility in hexane?

WWU -- Chemistry Solubility Rule “Like Dissolves Like”

WWU -- Chemistry Why Does The Rule Work? If a substance is to dissolve in a solvent, the intermolecular attractions between solute molecules and solvent molecules must be similar in strength as the solute-solute and solvent- solvent intermolecular attractions.

WWU -- Chemistry Types of Intermolecular Attractions Dipole-dipole attractions Hydrogen-bonding Van der Waal (London) forces

WWU -- Chemistry Part B. Solubility of Different Alcohols Solutes:Solvents –Water –Hexane

WWU -- Chemistry All three of these alcohols have a polar hydroxyl group. However, the rest of the molecule has a non-polar hydrocarbon chain.

WWU -- Chemistry How does the length of the carbon chain influence the solubility of the test alcohol in water? How does the length of the carbon chain influence the solubility of the test alcohol in hexane? What accounts for any differences?

WWU -- Chemistry Part C. Miscible or Immiscible Pairs Here we examine pairs of compounds to determine whether or not they are miscible (soluble). How do differences in polarity affect solubility? How do intermolecular attractions influence the solubility of a solute in a particular solvent?

WWU -- Chemistry Part D. Solubility of Organic Acids and Bases Solutes:

WWU -- Chemistry What is the important component in 1.0 M NaOH? What is the important component in 1.0 M HCl? What principle explains the solubility of a substance in aqueous acid or aqueous base?

WWU -- Chemistry Many covalent organic molecules are not very soluble in water even if they are somewhat polar! Benzoic acid is an example. When benzoic acid is reacted with sodium hydroxide, it is converted to an ionic substance (sodium salt), The ionic substance is now much more soluble in water! Ionic substances are very polar!

WWU -- Chemistry When benzoic acid reacts with sodium hydroxide, what happens to the covalent molecule?

WWU -- Chemistry Ionic compounds are soluble in water! Benzoic acid is converted to an ionic compound!

WWU -- Chemistry Compounds with amino groups are basic. They will become ionic when reacted with an acid because the lone pair on the nitrogen atom becomes bonded to a proton which creates an ionic substance.

WWU -- Chemistry So, what would you expect for the behavior of ethyl 4-aminobenzoate in acid solution and basic solution?

WWU -- Chemistry Remember This… Ionic compounds are usually very soluble in water. Consider Na + Cl - Higher molecular weight compounds with covalent bonds are usually insoluble in water If the covalent compound can be converted to ions, it will dissolve in aqueous solution!

WWU -- Chemistry Part E. Critical Thinking Application Skip this section

WWU -- Chemistry Experiment 3: Crystallization Reading Assignment: –Experiment 3 (pp ) –Technique 6 (pp ) –Technique 7 (pp ) –Technique 8 (pp ) –Technique 9 (pp ) –Technique 11 (pp )

WWU -- Chemistry Experiment 3 Note that this is a two-day experiment Plan on using your time as follows, or as your instructor suggests: –First day: Part A and part B –Second day: Part C

WWU -- Chemistry Experiment 3 NOTE CAREFULLY: –Although the textbook does not say to submit your samples with your laboratory report, the laboratory report sheet does! –Be sure to submit your purified samples of sulfanilamide and fluorene in separate labeled vials.

WWU -- Chemistry Experiment 3 If you do not obtain 150 mg of sulfanilamide crystals for Part A or 45 mg of crystals for Part B, expect to repeat the procedure until you get it right. The key is to figure out how to get crystals to form using the minimum amount of solvent.

WWU -- Chemistry Experiment 3 There is a pre-lab exercise that is due to your instructor before beginning this experiment. The 4th edition of the textbook doesn't have the data for sulfanilamide (although you could guesstimate from the graph on page 648, figure 11.2). Use the following data, instead: 0 deg -- solubility 14 mg/mL 20 deg -- solubility 24 mg/mL 40 deg -- solubility 46 mg/mL 60 deg -- solubility 88 mg/mL 78 deg -- solubility 210 mg/mL

WWU -- Chemistry Consult your section’s syllabus for the due date for post-laboratory report. Remember to submit the samples with your laboratory report!

WWU -- Chemistry Part A. Semimicroscale Crystallization –Use an Erlenmeyer flask and Hirsch funnel Part B. Microscale Crystallization –Use a Craig tube Part C. Selecting a Solvent to Crystallize a Substance Part D. Critical Thinking Application –Skip this section

WWU -- Chemistry

Semimicroscale crystallization using vacuum filtration: Part A

WWU -- Chemistry Microscale crystallization using a Craig Tube: Part B

WWU -- Chemistry Craig Tube + Centrifuge Tube

WWU -- Chemistry Solubility – Types of Solutions Saturated: The solution contains the maximum amount of solute that it can hold at that temperature. No more solute can be dissolved. Unsaturated: The solution contains less than the maximum amount of solute that it can hold at that temperature. More solute can be dissolved. Supersaturated: The solution contains more solute than the maximum amount of solute that it can hold at that temperature. A supersaturated solution is unstable; a precipitate (or crystals) is likely to form if the solution is disturbed.

WWU -- Chemistry Crystal Formation A dissolved material will separate from the solution as it is cooled. If the crystal growth is slow and selective, that is crystallization If the crystal growth process is rapid and nonselective, that is precipitation. In crystal growth, molecules arranged themselves into a highly specific structure called a crystal lattice.

WWU -- Chemistry Crystal Formation A successful crystallization depends on a large difference between the solubility of a material in a hot solvent and its solubility in the same solvent when it is cold. A material can be purified by crystallization when both the desired product and the impurity have similar solubilities, but only when the impurity represents a small fraction of the total solid.

WWU -- Chemistry Solubility versus Temperature

WWU -- Chemistry Solubility of Sulfanilamide in 95% ethanol-water

WWU -- Chemistry What Are The Characteristics of a Good Crystallization Solvent? There should be a large difference in solubility between hot and cold solvent The boiling point of the solvent should be well below the melting point of the solute. The solvent must not react with the solute The solvent should have a low boiling point (makes removal of the solvent easy) The solvent should be non-toxic The solvent should be innocuous The solvent should not be expensive

WWU -- Chemistry Crystallization: Technique You should always do a crystallization in an Erlenmeyer flask or in a Craig tube. Do not use a beaker or a round- bottom flask for crystallization.

WWU -- Chemistry Semi-microscale Crystallization

WWU -- Chemistry Good Laboratory Practice When you isolate crystals, allow them to air dry overnight. Wait until the following day to determine the weight or the melting point.

WWU -- Chemistry Determining Melting Points READ: Technique 9 (pp. 627 – 637)

WWU -- Chemistry Melting point-Composition Curve

WWU -- Chemistry Normal expectation for the melting point of an impure compound: 1.The melting point will be low compared to the literature value. 2. The melting point is never a single number! You will observe a range from when it starts to melt to when it has melted completely. Melting point

WWU -- Chemistry Mixture Melting Points The melting point can be used in identifying a compound. 1.One can compare the melting points of a known and an unknown compound. 2.If an unknown solid is mixed carefully with an equal amount of known compound, one can then determine the melting point of the mixture

WWU -- Chemistry Mixture Melting Points If the melting point of the mixture is identical to the melting points of the two separate substances, we may say that the two substances are identical. If the melting point of the mixture is depressed, it is clear that the known and the unknown are different substances.