CHEM 343 Lab Final Exam | Questions with Verified Answers

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CHEM 343 Lab Final Exam | Questions with Verified Answers Acetic acid is a weak acid. When acetic acid dissolves in water to make a solution, what is the major form of acid in the solution? a. Wate... r b. Hydronium ion c. Acetate ion d. Hydroxide ion e. Acetic acid Rank the following compounds in order of their increasing pKa (lowest pKa to highest): water, methane, benzoic acid, HCl a. HCl, water, benzoic acid, methane b. HCl, benzoic acid, water, methane c. water, methane, HCl, benzoic acid d. benzoic acid, HCl, water, methane e. methane, water, benzoic acid, HCl As in part B of exp. 1, when the graphs are made properly, the density of the liquid can be obtained via: a. Slope b. R-square c. y-intercept Which of the following is mostly insoluble in water? a. Hydrochloric acid b. Sodium chloride c. Benzoic acid d. Sodium benzoate From the lecture, which one of the following is not one of the five basic categories of organic lab work? a. Heating b. Analysis c. Separation d. Organic reaction In the acid-base reaction from experiment 1, what is the conjugate acid? a. Hydrochloric acid b. Benzoic acid c. Sodium chloride d. Sodium benzoate If a student added HCl(aq) to sodium benzoate and stopped around pH 3 (instead of 2 as described in the lab procedure), how would this affect the % yield of this experiment? a. This change will impact % purity more than % yield b. Lower % yield c. Higher % yield Name two pieces of equipment essential for carrying out vacuum filtration: a. Buchner funnel b. Side-arm flask c. Short-stem funnel d. Erlenmeyer flask e. Beaker Imagine an organic liquid A has a density of 0.825 g/mL and is mixed with water. Assume this organic liquid does not dissolve in water, then the top layer must be: a. Organic b. Aqueous If you need 9.49 mmol sodium benzoate as a starting material, what mass, in grams, would you add to the reaction.(MW of sodium benzoate is 144.1 g/mol, the density is 1.44 g/mL)? 1.37g Which of the following is used to separate aqueous and organic liquids? a. Buchner funnel b. Separatory flask c. Separation tube d. Separatory funnel If methylene chloride has a density of 1.34 g/mL and was used in an extraction with an aqueous solution, which would be the bottom layer in the separatory funnel? a. Organic b. Aqueous Acetaminophen is the chemical name of what common drug? a. Ibuprofen b. Morphine c. Aleve d. Tylenol Why would a compound with more h-bonds be more soluble in water? h-bond interactions allow for bonds to be broken, allowing for better dissociation (solubility) Which of the following outcomes would most possibly occur if you acidified sodium acetylsalicylate to pH 4 instead of pH 2? a. Falsely low % recovery of aspirin b. Falsely low % recovery of unknown c. Falsely low % recovery of sucrose d. Falsely high % recovery of aspirin What ingredient of Panacetin is the most acidic and most easily ionizable in the presence of a base? a. Panacetin b. Sodium acetylsalicylate c. Sucrose d. Acetylsalicylic acid If you want to make 41 mL of 0.2 M NaOH solution, what mass (in grams) of NaOH would you need to dissolve? (Use the molecular weight of NaOH as 40 g/mol) 0.33g What makes alcohols less soluble in room temperature water? long carbon chains Which of the following outcomes would most possibly occur if you initially dissolved the panacetin mixture in a more polar organic solvent, still immiscible in water, instead of dichloromethane? a. Falsely high % recovery of sucrose b. Falsely low % recovery of aspirin c. Falsely low % recovery of sucrose d. Falsely low % recovery of unknown What results when too much solvent is used to dissolve the product in recrystallization? a. Product loss - too much solvent dissolves more product b. The melting point range raises and becomes more narrow c. Improper/incomplete recrystallization - more solvent-solvent interactions do not allow for complete dissociation of the product d. Falsely high percent recovery - extra solvent is contributing to mass If an impurity exists in a sample, the melting point _________ and ________. a. Raises and narrows b. Lowers and narrows c. Lowers and broadens d. Raises and broadens If the solubility of phenacetin is 1.22g/100mL solvent, how much solid (in grams) could be dissolved in 32 mL of solvent? 0.39g In this experiment, how are you determining the identity of the unknown? a. Boiling point b. 2 of these are correct c. Melting point d. Density What is the purification method used in Experiment 3? a. Separation b. Recrystallization c. Distillation d. Melting point When recrystallizing, it is important to have an appropriate solvent. Select all that are characteristics of a good solvent. a. When hot the solvent dissolves a large amount of the compound b. Completely dissolves impurities c. Partially dissolves impurities d. When cold, the solvent dissolves a large amount of the compound e. Boils above the compounds melting point f. Inexpensive g. Is volatile enough that crystallized solid can be dried h. Does not react chemically with the compound Why is it important to slowly cool the product after recrystallization? a. Allows time for ALL of the product to settle at the bottom b. Allows for accurate tracing of temperature, from which we can calculate the lattice energy, and thereby identify the compound c. Allows perfect crystals to form, effectively removing all impurities d. Allows impurities to fully dissolve, since many are more soluble in cold water If you have 2.6g of an unknown, how much boiling water is needed to dissolve that substance? (solub. b.w. of unknown is 0.046 g/mL; density of water is 1.00 g/mL). a. 565 mL b. 56.5 mL c. 0.12 mL d. 120 mL What are some of the disadvantages of using recrystallization? Select all that apply. a. Products are always somewhat soluble - product loss is inevitable b. It is an expensive technique since one needs a recrystallizer instrument c. It is a time consuming process d. Identifying the proper solvent is difficult in most cases What is one way to identify a compound using instrumental analysis? a. Color b. Melting point c. Density d. Boiling point e. NMR spectroscopy Why would we use water as a solvent instead of dichloromethane (DCM)? a. Water will dissolve the product and it will be ideal to separate b. Water is not reactive, DCM is. c. DCM boils at a low temperature, the reaction needs to have the maximum energy input d. DCM boils at a low temperature all of it would evaporate and your rxn would scorch What is the ideal pH for experiment 4 after adding acid? Explain what would happen if the acid wasn't added to make the pH in this range. 2; Yield would decrease Which statement(s) are INCORRECT regarding reflux? a. Capping the reflux apparatus prevents loss of product b. Reflux is used to overcome large activation energies in organic reactions c. 2 of the above d. All of the above e. None of the above f. A hot water bath always provides sufficient energy to complete the reaction g. The boiling point is an important factor when selecting a solvent How would IR spectroscopy be used to quickly analyze the correct formation of product? a. A new aromatic peak will show up for product b. Loss of Ester peak c. Loss of OH group peak d. Gain of Carboxylic acid peak Give 2 reasons or indications that the reaction was successful. These should be empirical observations immediately obtainable after reflux, not from instrumental analysis. a. A solid is formed after acid addition b. A solid is formed after reflux c. MP range is good d. The reflux mixture is cloudy e. The reflux mixture evaporates f. It no longer smells like wintergreen oil g. It smells like wintergreen oil h. IR analysis shows a carboxylic acid You are preparing to begin the Exp. 5 synthesis using 6.01 mL of isopentyl alcohol. Calculate the mmols for this amount of reagent used. 55.6 mmol What role does sulfuric acid play in this experiment? a. Catalyst b. Product c. Intermediate d. Reactant What salt is used to complex water molecules in attempts to remove them from an organic solution? a. Sodium hydroxide b. Sodium phosphate c. Sodium sulfate d. Potassium permanganate . What is the purpose of "washing" the reaction mixture with dilute NaHCO3? Why does it require more attention than usual to venting? Select all that apply. a. Bicarb is explosive b. To remove acid c. Bicarb makes CO2 d. To remove/extract product Between the two compounds, isopentyl acetate and isopentyl alcohol, which compound will elute out first during Normal-Phase Gas Chromatography? a. Isopentyl acetate b. Isopentyl alcohol What change in the IR absorption pattern will tell you that you synthesized Isopentyl Acetate? (Note: Please give both the correct structural features that are present and absent, in relation to the Isopentyl Alcohol) The presence of a sharp peak at ~1700 cm^-1 will show the presence of a carbonyl a. The lack of an OH peak around ~1700cm-1 b. Sharp peak at ~1700cm-1 will show carbonyl c. Broad peak at ~3400cm-1 will show a carbonyl d. The lack of an OH peak around ~3400cm-1 Why is the water wash after finishing the heat under reflux procedural step so important? a. It provides better IR reads b. It dilutes the acid c. It dilutes the sodium bicarbonate d. It recrystallizes product How may IR be used to help estimate the purity of your product in experiment 5? Select those that apply. a. The presence of an OH peak b. IR is quantitative - integrate the peaks and compare c. IR is not quantitative - GC would be better for estimation d. The lack of a carbonyl peak around ~1700cm-1 Which would be a suitable gas to use for the mobile phase of a reverse phase GC? a. Propane b. Water vapor c. Carbon dioxide d. 2 of the above e. Helium What issue would you run into if you used 100% 18M acetic acid as your TLC solvent in a normal phase TLC run? a. The plate would not develop in iodone b. The plate would not run c. The plate would float in the acetic acid In TLC, the Rf value of a compound will not change the longer the plate resides in the solvent chamber. a. True b. False The following table shows data for a sample that was run under normal phase GC conditions: Peak Ret. Time Peak Area Peak 1 1.15 min 105 cm2 Peak 2 3.5 min 60 cm2 Peak 3 5.0 min 75 cm2 What is the percent composition of the most polar species? Answer to 2 decimal places. The running gas is not reported as a peak. 31.25% Vitamin A, vitamin B, and vitamin C are three important biological supplements. Vitamin C is the most water soluble. Vitamin A is the least water soluble. Vitamin B is in between. 1. Which compound is the most polar? 2. Which compound will have the highest Rf value? 1. Vitamin C 2. Vitamin A Explain why it is important to use pencil when drawing your spotting line on the TLC plate? a. Pencil marks are not visible after iodine b. Pencil markings do not run up the plate c. Pencil markings are more visible after being exposed to the iodine d. Pencil markings run up the plate How can compound Y, which has a higher boiling point than compound Z, elute before compound Z in a normal phase GC? [Show More]

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