View
277
Download
7
Category
Tags:
Preview:
Citation preview
WWU -- ChemistryWWU -- Chemistry
Chemistry 354Organic Chemistry
Laboratory I
WWU -- ChemistryWWU -- Chemistry
Safety
The organic chemistry safety presentation on the web is available on the web at the following address:
http://atom.chem.wwu.edu/dept/osafety/index.htm. Read pp 542 – 558 in the lab book. We administer the
safety quiz online at the following URL:http://argon.chem.wwu.edu/SafetyQ/OCQLink.htm 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 -- ChemistryWWU -- Chemistry
SafetyFirst 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 0.050 to 0.100 grams. Glassware containers up to 25 mL.
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Experiment 2: Solubility
• Reading Assignment– Experiment 2 (pp.13 – 20)– Technique 5 (pp. 581 – 589)– Technique 10 (pp. 637 – 646)
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Solubility
• The extent to which a substance is soluble in a solvent.
• Examples (solubility in water at 25°C):– Cholesterol 0.002 mg/mL– Caffeine 22 mg/mL– Citric acid 620 mg/mL
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Part A: Solubility in a Series of Solvents
C
O
CH2C CHO
O
OH
O
Benzophenone
Malonic acid
Biphenyl
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Make a guess as to the solubility of malonic acid inwater. Notice that the acid has two very polar carboxylgroups in the compound.
CH2C CHO
O
OH
O
Malonic acid
Would you expect this compound to be soluble inthe non-polar hexane solvent?
WWU -- ChemistryWWU -- Chemistry
How consider the solubility of biphenyl in water. Make a guess as to the whether it will be soluble in water.
Biphenyl
What about the solubility in hexane?
WWU -- ChemistryWWU -- Chemistry
Solubility Rule
“Like Dissolves Like”
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Types of Intermolecular Attractions
• Dipole-dipole attractions
• Hydrogen-bonding
• Van der Waal (London) forces
WWU -- ChemistryWWU -- Chemistry
Part B. Solubility of Different Alcohols
• Solutes: • Solvents– Water– Hexane
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 OH
1-Octanol
CH3 CH2 CH2 CH2 OH
1-Butanol
CH3 OH
Methanol
WWU -- ChemistryWWU -- Chemistry
OH1-octanol
OH 1-butanol
C OH
H
H
H
methanol
All three of these alcohols have a polar hydroxylgroup. However, the rest of the molecule has a non-polar hydrocarbon chain.
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Part D. Solubility of Organic Acids and Bases
• Solutes:
C OH
O
H2N C O
O
CH2 CH3
Benzoic acid
Ethyl 4-aminobenzoate
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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!
O
OH
Acidic carboxylgroup
WWU -- ChemistryWWU -- Chemistry
• When benzoic acid reacts with sodium hydroxide, what happens to the covalent molecule?
O HO-H
Na
O
WWU -- ChemistryWWU -- Chemistry
O Na HO
H
O
+
Ionic compounds are soluble in water!
Benzoic acid is converted to an ionic compound!
WWU -- ChemistryWWU -- Chemistry
Compounds with amino groups are basic. Theywill become ionic when reacted with an acid becausethe lone pair on the nitrogen atom becomes bondedto a proton which creates an ionic substance.
NH
HH-Cl
NH
H
HCl
Covalent amino compoundinsoluble in water
Ionic compound is soluble in aqueousacid solution!
H2O
WWU -- ChemistryWWU -- Chemistry
So, what would you expect for the behavior of ethyl 4-aminobenzoate in acid solution and basic solution?
H2N C O
O
CH2 CH3
Ethyl 4-aminobenzoate
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Part E. Critical Thinking Application
• Skip this section
WWU -- ChemistryWWU -- Chemistry
Experiment 3: Crystallization
• Reading Assignment:– Experiment 3 (pp. 21-32)– Technique 6 (pp. 589-597)– Technique 7 (pp. 598-616)– Technique 8 (pp. 616-627)– Technique 9 (pp. 627-637)– Technique 11 (pp. 647-668)
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Consult your section’s syllabus for the due date for post-laboratory report.
Remember to submit the samples with your laboratory report!
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
H2N S NH2
O
O
Sulfanilamide
m.p. = 165 - 167°
Fluorene
m.p. = 114 - 116°
WWU -- ChemistryWWU -- Chemistry
Semimicroscale crystallization using vacuum filtration: Part A
WWU -- ChemistryWWU -- Chemistry
Microscale crystallization using a Craig Tube: Part B
WWU -- ChemistryWWU -- Chemistry
Craig Tube + Centrifuge Tube
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Solubility versus Temperature
WWU -- ChemistryWWU -- Chemistry
Solubility of Sulfanilamide in 95% ethanol-water
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Semi-microscale Crystallization
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- Chemistry
Determining Melting Points
• READ: Technique 9 (pp. 627 – 637)
WWU -- ChemistryWWU -- Chemistry
Melting point-Composition Curve
WWU -- ChemistryWWU -- 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 -- ChemistryWWU -- 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 -- ChemistryWWU -- 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.
Recommended