Organic Chemistry Laboratory 2230 Final Exam Study Guide

Transcription

1 Organic Chemistry Laboratory 2230 Final Exam Study Guide Many students do not adequately prepare for the final exam in 2230L.The average grade is typically in the mid to upper 60 s. Each semester, some students score in the 90 s, and unfortunately some score in the 40 s or below. It is not unusual for a student to drop a letter grade due to poor performance on the final exam. To prepare for your final exam, it is a good idea to do the following; re-read all on-line notes associated with each experiment, read through the notes you took during each pre-lab lecture, and review all of your old quizzes. In the procedure document of each experiment is a list of topics that a well prepared student should be able to answer or explain. Ensure you understand each of these. Make sure you get all of your questions answered and understood well before the final exam. Two minutes before the final exam is scheduled to begin is not the time to ask questions. Following is a partial list of topics that 2230L has covered over the duration of the class. It is not complete. You should be familiar with each of these topics. Disclaimer: This study guide is to aid you in your studies. If something is or is not present on this study guide it does not mean it will or will not appear on the final exam. General Know the names of all glassware. Know relevant safety procedures. Know how to safely dispose of chemicals and other lab waste. Know general lab techniques. Know proper notebook techniques. Know proper weighing techniques. Know what procedure should be done to accomplish specific goals such as purification of solids, purifications of liquids, functional group analysis, separation of solids, separation of liquids, and material identification. Safety What are some of the terms used to describe the potential dangers of a chemical compound? What is a flash point and what is it used for? What is a LD50? What is a flammable material? Inflammable? Combustable? What is a corrosive material? Mutagen? Teratogen? Carcinogen? Lachrymator? Irritant? Toxic? What is a MSDS and why is it important? What are some precautions taking when working with highly reactive chemicals? What are PPE? Melting Points Thermometer safety What properties should and ideal melt point/range contain?

2 What effects if any does soluble impurities have on melt point / range? Insoluble impurities? Is melting point a physical or chemical property and why? How does the following factors influence melting point? Molecular weight, polarity, hydrogen bonding, branching Should a melting point/ range be taken fast or slow? IF given a series of mixed melting points, be able to identify composition. If given a melting point range and the literature value, be able to assess the purity of the sample. Infrared Define the main regions of interest in the IR. What are the frequency ranges and groups are represented in each region? Understand how the identify a functional group based on the peak location, shape or intensity. Explain in simple terms how an infrared works. Explain the Electromagnetic spectrum What is wavenumber and how is it calculated? Understand the relationship between wavenumber and energy. Is a larger wavenumber higher or lower in energy? Frequency? Be able to recognize the IR spectrum of the following functional groups: terminal alkyne, alkyne, nitrile, carboxylic acid, alcohol, primary amine, secondary amine, alkane, carbonyl, ketone, ester, ether linkage. Be able to select the proper IR if given a structure. Be able to select the proper structure if given an IR spectrum. TLC & Column Know how to calculate Rf. How is the purity of a reaction mixture determined using TLC? How is the identity of a product in a reaction mixture determined using TLC? Given a set of TLC plates or Rf values, be able to determine reaction outcomes. IF F is a starting material and four syntheses were run, what does each plate indicate? Given two structures predict which will have a lower Rf. Given 2 Rf s predict which compound is more polar. How are TLC and column chromatography similar and differ? (i. e. capillary vs. gravity used for separation) What are the various layers in column chromatography and explain their purpose? Why were the solvents introduced into the column in a particular order?

3 What concept or process allow for separation in column chromatography? ( Hint: review all note dealing with separation) What is a mobile phase? Give an example What is a stationary phase? Give an example Distillation Why was a copper mesh used? Why is placement of thermometer important? How to properly read a thermometer? Know names of each piece of glassware. What is a theoretical plate and why is it important? What is reflux and why is it preformed? What is a major safety concern when refluxing? (Hint: formation of peroxide ) When is better to perform a factional distillation over a simple distillation? Be able to properly interpret a distillation composition diagram (see notes.) Recrystallization What is the purpose of recrystallization? Be able to take weight by difference. What are the properties of a good recrystallization solvent? What is percent recovery and how is it calculated? What error/s effect only purity or percent recovery or both? (Review notes, data sheet and quiz) If given an experimental action, be able to predict the effect on purity or percent recovery. Is it possible to have percent yield greater than 100%? Be able to draw structure of all chemicals used in this experiment. When recrystallization why should solvent be added until the entire solid dissolves and no more? What happens if additional solvent is added? What happens if not enough solvent was added? Why should the product be allowed to crystallize slowly and not plunge directly into ice water? Separation of Acidic Substances What type of extraction is used in this experiment? The first extraction of benzoic acid and 2-naphthol why do we use NaHCO3? The second extraction of BA and 2-naphthol why do we use NaOH? What forms when the acids are mixed with the bases? Explain partitioning. Explain what drives a compound to move from one phase to another. If given a series of structures be able to predict the highest solubility in a given phase.

4 What would happen if you extracted a solution containing both a strong and weak acid with NaOH? S.A. + S.B W.B. + W.A. W.B. +W.A. x-> S.A. + S.B. Looking at pka values, what makes a reaction proceed to the right What is the purpose of the HCl? What product forms once NaHCO3 has been added? What product forms once NaOH has been added? Know the solubility changes from benzoic acid to sodium benzoate. What would cause a low % recovery for BA? What would cause a higher % recovery for 2-Naphthol? Know safety about using concentracted NaOH and HCl. If given a set of Pkas, be able to predict if the reaction will proceed in the forward direction or not. Gas Chromatography Explain chromatography. Explain how GC works. What properties dictate the relative retention time of a series of chemicals. Be able to predict the impact on retention time by changing column temperature, flow rate, sample size, column length. If given a GC trace, be able to calculate the retention time and percent composition of any peak. Be able to read a GC and understand the composition of a sample. What unique safety concerns are associated with a GC. Refractive Index Explain in simple terms how a RI works. Be able to accurately read a RI graph. Be able to calculate a corrected RI value if given a RI for water and the compound. Be able to select the proper identification of a sample if given experimental RI values and a list of possible materials with their RI. Stereochemistry Know how to identify a chiral or achiral compound. Know how to identify stereocenters. Know how to identify different types of isomers. Know how to identify the type of compound: same, constitutional, diasteromer, enantiomers, meso. Know how to assign priority and R and S configuration. Know how to calculate specific rotation. If given the specific rotation of a mixture and the specific rotations of the pure compounds, calculate the composition of the mixture. Isolation of Caffeine

5 What type of extractions take place during this reaction? What is the purpose of Na2CO3? What is an emulsion? We use dichloromethane in this experiment, where should the excess waste be placed? Know how to calculate Rf. How is the purity of a reaction mixture determined using TLC? How is the identity of caffeine in the reaction mixture determined using TLC? Know how to calculate the % of caffeine. Review solubility of caffeine in water and CH2Cl2. How would the following impact % caffeine recovered: -Too much sodium sulfate was used -Too little sodium sulfate was used -Some black aqueous was removed with the clear CH2Cl2 layer -Some water condensed on watch glass when drying -The bag and string were weighed along with the tea -Some tea spilled on while transferring to centrifuge tube. SN1 Know the mechanism. Know the relative stability of carbocation. What is sodium bicarbonate? What is sodium biocarbonate, NaHCO3 used for in this reaction? What is sodium chloride called in this reaction (not salt)? What is the sodium chloride used for in this reaction? Know why the product separates from the starting material. Know why or how silver nitrate test is used to analyze the product. What should happen to the ph of the test solution after silver nitrate was added to the product? What does SN1 mean? What is sodium sulfate and what role does it perform? What is the purpose of using sodium sulfate in this experiment? Know how to calculate the % yield. Know safety associated with using concentrated HCL. Qualitative Analysis 1 If given a boiling point, RI and IR be able to select identification of compound. Percent Yield Be able to calculate theoretical maximum amount of product and limiting reagent for any reaction. The starting materials may be neat liquids, solutions or solids.