Identifying an Unknown Compound by Solubility Functional

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contain only a single type of these functional groups Each of these functional groups has a unique. combination of solubility and reactivity that allows it to be distinguished from the others. In Part A of the experiment Week 1 you will use solubility tests to characterize your unknown. compound By comparing the solubility of your unknown in several aqueous solutions described below. you will be able to limit the possible functional groups on your compound A flow chart Figure 2 will help. guide you in this effort In some cases these tests will be sufficient to identify the functional group s of. your unknown substance, In Part B of the lab Week 2 you will conduct a series of experiments to distinguish between the. remaining functional group possibilities to uniquely identify the functional group on your unknown. compound You should note that in most cases with proper planning and utilization of the information. gained in Part 1 only a few functional group tests will be required to uniquely identify the functional. group s contained within your molecule You will not need to run all of the chemical tests on each. sample You job is to decide which are needed for each unknown in order to determine its functional. group s If you are not thoughtful in this process and try to run all of the tests you will likely run out of. material see below, Each group will be given approximately 1 gram of two different unknown samples You must. carefully think about what tests you wish to conduct as not to waste your sample If you carelessly run too. many tests and exhaust your material you can obtain an additional sample of your unknown from your. TA Additional sample will cost you 10 of your grade for this lab per additional sample required. Take home message plan your experiments carefully, For both Part A and Part B several known compounds will also be available so you can compare. your results from your unknown to both known positive and negative tests Figure 1 lists the known. compounds that will be available to you Tables 1 and 2 outline known substrates for each of the tests. Figure 1 List of Known Compounds Available For Use As Positive and Negative Standards. OMe t Bu Me Me, 3 propanone 3 4 dimethoxybenzaldehyde 4 tert butylphenol 2 propanol 1 propanol cyclohexene. Me Me Me OH Me Me,Me Cl Me N,Cl O Me Me, hexane 1 chloropentane tert butylchloride octanoic acid diisobuytlamine.
In Part C of the lab take home once you have correctly identified the functional group present in. your unknown compounds your TA will provide you with the H NMR and C NMR spectra for your. compounds as well as the compound s molecular formula From this data and the results of your. experiments above you will then assign the structure of the unknown and label the spectral data. PART A WEEK 1 SOLUBILITY TESTS, Organic compounds follow three interdependent rules of solubility. 1 small organic molecules are more soluble in water than are large organic molecules. 2 polar organic molecules especially those capable of hydrogen bonding are more soluble in water. than are nonpolar molecules and, 3 compounds in their ionic forms are more soluble in water than their neutral forms. For example benzoic acid is not soluble in water yet it is soluble in sodium hydroxide solution. and in sodium hydrogen carbonate solution because these bases react with benzoic acid to form the. water soluble benzoate ion The solubility of carboxylic acids and amines is so characteristic that. solubility tests alone differentiate these functional groups from all the others in this experiment. The solubility flowchart shown in Figure 2 provides the scheme for this experiment The first test. to perform on all unknowns is water solubility,Figure 2 Solubility Test Flow Chart. water insoluable,test solution with pH paper,insoluable soluble. 5 HCl 5 NaHCO3,soluable insoluable soluable insoluable.
bubbles no bubbles soluble insoluable bubbles no bubbles. amine carboxylic acid phenol,carboxylic acid low mol mass conc H2SO4. alcohol aldehyde,ketone amine insoluable,soluable color change no color change. alkene alcohol,aldehyde ketone alkane alkyl halide. Small polar organic compounds such as alcohols aldehydes ketones amines carboxylic acids and a. few phenols are soluble in water Water soluble compounds are tested with pH paper to see if they are. acidic or basic A pH of 4 or lower indicates a carboxylic acid A pH of 8 or higher indicates an amine. Water soluble compounds are tested with 5 sodium hydrogen carbonate NaHCO3 to. determine whether or not they are carboxylic acids Carboxylic acids react with NaHCO3 to produce. carbon dioxide bubbles as shown below in Equation 3. Large alcohols aldehydes ketones amines carboxylic acids and phenols are not soluble in. water Alkanes alkyl halides and alkenes are not soluble in water regardless of their size These water. insoluble compounds are tested for their solubility in the following reagents. 5 Sodium Hydroxide, Water insoluble compounds are first tested with 5 sodium hydroxide NaOH Sodium hydroxide is a. strong base that ionizes strong or weak Figure 2 Solubility flowchart acids Thus both carboxylic acids. and phenols are converted to salts and dissolve in aqueous solution Non acidic compounds will not. dissolve The reactions of carboxylic acids and phenols are shown in Equations 1 and 2 respectively. NaOH aq H2O eq 1,R OH R O Na,carboxylic acid water soluble.
NaOH aq H2O eq 2,substituted water soluble,5 Sodium Hydrogen Carbonate. Water insoluble compounds that are soluble in 5 NaOH are then tested with 5 sodium hydrogen. carbonate NaHCO3 Strongly acidic compounds such as carboxylic acids react with NaHCO3 to form. water soluble salts as shown in Equation 3 The reaction also produces bubbles of carbon dioxide. This test is commonly misinterpreted because CO2 bubbles are tiny Careful observation is. Phenols are less acidic than carboxylic acids and do not react with NaHCO3 to form water soluble. salts As a result phenols are insoluble in 5 NaCHO3. NaHCO3 aq H2CO3 eq 3,R OH R O Na,carboxylic acid water soluble H2O CO2. 5 Hydrochloric Acid, Water insoluble compounds that are insoluble in 5 NaOH are tested with 5 hydrochloric acid HCl If. a compound is soluble in 5 HCl it is an amine Amines are organic bases that react with HCl to form. water soluble amine salts as shown in Equation 4,R R HCl aq N eq 4. amine water soluble,Concentrated Sulfuric Acid, Water insoluble compounds that are insoluble in 5 HCl are tested with concentrated sulfuric acid.
H2SO4 Virtually all organic compounds containing alkene functional groups or oxygen or nitrogen. atoms are soluble in concentrated H2SO4 These functional groups typically react with H2SO4 to form new. compounds Only alkanes alkyl halides and some aromatic compounds are insoluble in H2SO4. Table 1 Known Positive And Known Negative Test Compounds For Solubility Tests. solvent positive test negative test,water isopropanol 3 4 dimethoxybenzaldehyde. 5 NaOH 4 tert butylphenol 3 4 dimethoxybenzaldehyde. 5 NaHCO3 octanoic acid 3 4 dimethoxybenzaldehyde,5 HCl diisobutylamine 3 4 dimethoxybenzaldehyde. H2SO4 cyclohexene hexane,PROCEDURE PART A WEEK 1, Perform the water solubility test on the known positive known negative and unknown. Perform subsequent solubility tests, If the solubility tests point to a carboxylic acid or amine the classification is complete. If the solubility tests suggest any other functional groups you will preform classification tests. during week 2 appropriate to those groups until the unknown is narrowed to only one functional. Microspatula glass stirring rod, 10 mL graduated cylinder 6 10 test tubes 15 x 125 mm.
6 10 test tubes 10 x 75 mm test tube rack,pH paper 1 0 mL transfer pipet. Pasteur pipet with latex bulb,Solubility Tests, CAUTION Wear departmentally approved safety goggles at all times while in the chemistry. laboratory, Always use caution in the laboratory Many chemicals are potentially harmful Follow. safety precautions given for all reagents used in this experiment Prevent contact with your eyes. skin and clothing Avoid ingesting any of the reagents. Perform all tests in duplicate using an unknown a known positive and a known negative Mix well to. make certain that liquid samples are not floating in the meniscus Allow several minutes for compounds. to dissolve Be patient and observe closely, Conduct the solubility tests following the pattern shown in Figure 1 above Verify your solubility. test results with your laboratory instructor before performing the classifications tests in Part 2 Use clean. test tubes for each test,1 Performing the Water Solubility Test.
CAUTION Unknowns may be flammable toxic corrosive or irritating Keep away from flames or. other heat sources, Add 1 drops of a liquid sample or about 25 mg of a solid sample to 0 5 mL of distilled or deionized water. in a test tube Tap the tube with your finger to mix or stir gently with a glass stirring rod Record the. sample as soluble or insoluble, If the unknown is water soluble test the solution with pH paper Also test the pH of water as a. A solution at pH 4 of lower suggests a carboxylic acid A solution at pH 8 or higher suggests an. 2 Performing the 5 Sodium Hydroxide Solubility Test. CAUTION Sodium hydroxide NaOH and hydrochloric acid HCl are toxic and corrosive. If your compound is water soluble proceed to Part 3. For water insoluble compounds add 1 drops of a liquid sample or about 25 mg of a solid sample to 0 5. mL of 5 NaOH in a test tube Tap the tube with your finger to mix or stir gently with a glass stirring rod. Record the sample as soluble or insoluble, To verify that a compound has dissolved add 5 HCl to the NaOH mixture until the solution is. acidic to pH paper Look for a precipitate indicating that the water soluble salt has converted back into. the water insoluble compound, Solubility in NaOH indicates either the carboxylic acid or phenol. 3 Performing the 5 Sodium Hydrogen Carbonate Solubility Test. a For Water Soluble Compounds, Put 1 drops of liquid sample or about 25 mg of solid sample in a dry test tube Add 0 5 mL of 5 sodium.
hydrogen carbonate NaHCO3 Do not stir Watch for bubbles at the interface of the phases Then tap. the tube with your finger to mix or stir gently with a glass stirring rod Record the sample as soluble or. Generation of bubbles and solubility indicates a carboxylic acid Solubility without generation of. bubbles indicates a low molar mass alcohol aldehyde ketone or amine Conduct classification tests to. determine which functional group is present, CAUTION Diethyl ether ether is highly flammable and toxic Keep away from flames or other. heat sources Use a fume hood, If no bubbles were observed put 1 drop of liquid sample or about 25 mg of solid sample in a dry. test tube Using a fume hood add about 0 5 mL of ether Then immediately add 0 5 mL of 5 NaHCO3. Observe whether or not bubbles are generated at the ether water interface. Generation of bubbles indicate a carboxylic acid,b For Water Insoluble Compounds. Put 1 drop of liquid sample or about 25 mg of solid sample in a dry test tube Add 0 5 mL of 5 sodium. hydrogen carbonate NaHCO3 Do not stir Watch for bubbles at the interface of the phases Then tap. the tube with your finger to mix or stir gently with a glass stirring rod Record the sample as soluble or. Generation of bubbles or solubility indicates a carboxylic acid. If the compound is not soluble in NaHCO3 but is soluble in NaOH it is likely a phenol Confirm. the presence of phenol with a phenol classification test. 4 Performing the 5 Hydrochloric Acid Solubility Test. CAUTION Hydrochloric acid HCl is toxic and corrosive. For compounds insoluble in water and insoluble in 5 NaOH add 1 drop of a liquid sample or about 25. mg of a solid sample to 0 5 mL of 5 HCl in a test tube Tap the tube with your finger to mix or stir gently. with a glass stirring rod Record the sample as soluble or insoluble. If the compound is soluble in 5 HCl it is most likely an amine. 5 Performing Concentrated Sulfuric Acid Solubility Test. CAUTION Concentrated sulfuric acid H2SO4 is toxic and oxidizing Use a fume hood when. working with H2SO4, If the compound is insoluble in 5 HCl and 5 NaOH add 1 drop of a liquid sample or about 25 mg of a. solid sample to 0 5 mL of concentrated sulfuric acid H2SO4 in a dry test tube Tap the tube with your. finger to mix or stir gently with a glass stirring rod Do not use a metal spatula. Record the sample as soluble or insoluble Interpret a color change or a precipitate as soluble. If the compound is soluble in H2SO4 the sample is an alkene an alcohol an aldehyde or a. ketone Conduct classification tests for each compound type. If the compound is insoluble in H2SO4 the sample is an alkane or an alkyl halide Conduct. classification tests for alkyl halides, If alkyl halide tests are negative the compound is an alkane.
Based upon the positive and negative results from the above experiments you should now be able. to narrow the possibilities for the functional group s present in your unknown sample You. should now carefully decide which experiments are needed during Part B Week 2 to distinguish. those possibilities,PART B WEEK 2 CLASSIFICATION TESTS. Solubility tests Week 1 alone can indicate whether an unknown compound in this experiment is a. Identifying an Unknown Compound by Solubility Functional Group Tests and Spectral Analysis This handout is a supplement to Signature Lab Series ANAL 0727 and contains material adapted from Signature Lab Series ANAL 0727 and 0728 Cengage Learning This lab contains material copywritten by

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