Materials Included In Kit

Additional Materials Required

Prelab Preparation

• Cerium(IV) Ammonium Nitrate, Acidified, 0.1 M: Dissolve 5.48 g of cerium( IV) ammonium nitrate in 100 mL of 0.3 M nitric acid solution. (Obtain or prepare 0.3 M nitric acid by appropriate dilution of a more concentrated acid solution, for example, by diluting 10 mL of 3 M HNO₃ to 100 mL. Always add acid to water.)
• Iron(III) Chloride, 1%: Dissolve 1 g of iron(III) chloride hexahydrate in 100 mL of deionized or distilled water. The solution may be slightly cloudy due to the presence of hydrated, colloidal iron(III) oxide. Filter if needed.
• Potassium Chromate, Acidified, 0.1 M: Dissolve 1.92 g of potassium chromate in 100 mL of 0.5 M sulfuric acid solution. (Obtain or prepare 0.5 M sulfuric acid by appropriate dilution of a more concentrated acid solution, for example, by diluting 8.3 mL of 6 M H₂SO₄ to 100 mL. Always add acid to water.)
• Tollens’ Reagent: This solution must be freshly prepared in situ on the day of the lab and may not be stored. Tollens’ reagent consists of ammoniacal silver nitrate. To prepare 50 mL of Tollens’ reagent, mix 10 mL of 5% silver nitrate solution with 5 mL of 10% sodium hydroxide solution. A brown precipitate of silver oxide, Ag₂O, will be observed. Add dilute ammonia solution (10 mL of concentrated, 17.4 M reagent ammonium hydroxide diluted to 100 mL with water) in 1-mL increments to the brown silver oxide mixture until the solid dissolves. The total amount of ammonium hydroxide needed should be about 15−20 mL. Do not add excess ammonia. When almost all of the precipitate has disappeared, dilute the Tollens’ reagent mixture to 50 mL with water.
• Excess Tollens’ reagent or leftover silverplating reaction mixtures must be rinsed immediately after use into a dedicated waste container with copious amounts of water. The mixed solution may form an explosive mixture upon standing or when dried out. Do not heat Tollens’ reagent mixtures.
• If desired, individual student groups may prepare the reagent for their immediate needs only by following the above procedure at 1/10 scale to obtain 5 mL of the solution. Please instruct and warn students of the hazards described above and the necessary safety precautions for the safe storage, handling and disposal of Tollens’ reagent.

Safety Precautions

Carry out all procedures in an operating fume hood. Acetaldehyde, acetone, ethanol and 2-propanol are highly flammable liquids and vapors. Keep away from heat, sparks and open flames. Tollens’ reagent contains silver nitrate in a highly basic solution. It is corrosive to skin and eyes and will stain skin and clothing. Leftover mixtures containing Tollens’ reagent may form potentially explosive materials if left standing and allowed to dry. Follow the instructor’s directions for disposing of the leftover Tollens’ reagent immediately after use. Rinse with copious amounts of water into a container for disposal of the silver waste. Cerium(IV) nitrate and potassium chromate solutions contain acid and are corrosive to skin and eyes. Iron(III) chloride and salicylic acid may cause serious eye irritation. Avoid contact of all chemicals with eyes and skin. Organic liquids are volatile solvents and may cause drowsiness or respiratory tract irritation if inhaled. Avoid breathing mist, vapors or spray. Acetaldehyde and potassium chromate solutions are suspected carcinogens and/or genetic and reproductive hazards that may damage an unborn child. Work with these compounds in an operating fume hood only and do not use them if you are pregnant. Wear chemical splash goggles, chemical-resistant gloves and a lab coat or chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. Remind students to wash hands thoroughly with soap and water before leaving the lab.

Disposal

Please consult your current Flinn Scientific Catalog and Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Always segregate reactive chemicals, such as potassium chromate, a strong oxidizer, in waste containers to avoid potential undesirable side reactions that may release heat or generate gases. Collect excess or unreacted potassium chromate test solutions in a designated container to prevent mixing with alcohols, which may release heat when oxidized. Warning: Tollens’ reagent may become unstable or explosive when concentrated or heated. Collect excess or unreacted Tollens’ reagent in a dedicated beaker or flask by rinsing the solution with copious amounts of water to avoid the formation of silver imide. Dissolved silver ions may be precipitated in the form of silver chloride by adding concentrated hydrochloric acid. The solid should be identified as a toxicity characteristic hazardous waste. Mixed aqueous organic solutions containing cerium(IV) and chromium(III) ions should be collected in a heavy-metal waste beaker designated for licensed hazardous waste disposal according to Flinn Suggested Disposal Method #27f. Depending on local regulations, mixed organic aqueous solutions containing low-molecular weight alcohols, aldehydes, and ketones may be collected in an aqueous organic waste container or rinsed down the drain with excess water according to Flinn Suggested Disposal Method #26b. Aqueous organic solutions containing iron(III) ions may be collected or treated in a similar manner. Record the identity and approximate amounts of all chemicals added to each waste container, as well as the date.

Lab Hints

• This experiment may be completed within 2 hours. To conserve materials, reduce the equipment needed, and minimize potential waste, set up the experiment as an activity-stations lab for the four separate activities (properties of alcohols, color tests for alcohols and phenols, qualitative tests for aldehydes and ketones, and natural product testing) in designated hood locations throughout the lab. Students may complete the activities and rotate through the stations in any order. For best results and to improve logistics and traffic flow we recommend setting up at least two stations for each activity.
• Cyclohexanol is a low-melting organic solid (mp, 23–25°C) at room temperature. The capped chemical bottle may be rinsed with warm tap water to prevent solidification and make it easier to dispense cyclohexanol as a liquid rather than as a solid. To prevent a sealed bottle from collapsing during storage, allow the loosely capped, warmed container to “cool” to room temperature before tightening and securing the cap.
• Reactions of primary and secondary alcohols with potassium chromate are not instantaneous—allow 3−5 minutes for complete reaction and observations. Oxidation releases heat; the test tubes may feel warm to the touch. Always collect excess or unreacted chromate test solutions in a separate heavy-metal waste container to prevent unwanted side reactions in disposal containers.
• Tollens’ reagent consists of an ammoniacal solution of silver nitrate (silver nitrate and ammonia). Aldehydes give a positive test, as oxidation of the aldehyde is accompanied by reduction of Ag⁺ ions to silver metal, which often plates out as a beautiful silver “mirror” on the inside of the test tube. This reaction may be demonstrated using dextrose (glucose) as a “reducing sugar” to prepare a silver metal flask or silver holiday ornaments. Please visit the Flinn Scientific Teaching Chemistry Video Series on the Flinn website (www.flinnsci.com) to view a video of this demonstration and download printed instructions for the “Silver Mirrors” activity.
• The risk of explosion for disposal of Tollens’ reagent is attributed to the potential formation of “fulminating silver” due to the formation of solid silver imide. This hazard may be avoided by following the safety precautions and disposal instructions—rinse with copious amounts of water. Do not concentrate and never heat the solution or leftover reaction mixtures.
• Aliphatic aldehydes and ketones may also be distinguished using Benedict’s test, a qualitative oxidation reaction using Cu²⁺ ions in basic solution. Oxidation of an aldehyde causes the reduction of blue Cu²⁺ ions to a red precipitate of copper(I) oxide, Cu₂O. Aromatic aldehydes, such as benzaldehyde and cinnamaldehyde, do not give a positive Benedict’s test due to competing disproportionation (oxidation−reduction) reactions in the highly basic solution. Reaction of benzaldehyde with Benedict’s solution gives a dense white precipitate of potassium benzoate, along with benzyl alcohol, which presumably remains in solution.
• Additional natural products may be incorporated into this experiment for qualitative structure proof—rose oil and hyacinth oil contain the alcohols phenylethanol and phenylpropanol, respectively; almond extract contains benzaldehyde; and the principal ingredient in vanilla extract is vanillin, a phenolic aldehyde, which should give positive tests with both iron(III) chloride and Tollens’ reagent.

Answers to Prelab Questions

1. The systematic names of alcohols are derived by adding the functional group ending -ol to the root name for the longest continuous carbon chain that contains the OH group. The carbon atom bearing the OH group is assigned the lower possible number and substituents are named and numbered using the same rules that apply to alkanes, alkenes, etc. Draw structures for or provide the systematic name for the compounds shown.
   {13798_PreLabAnswers_Figure_10}
2. Draw the Lewis structure of a methanol molecule, including any lone pair(s) of electrons, and show by means of dashed lines the hydrogen bonds that can form between methanol and three water molecules.
   {13798_PreLabAnswers_Figure_11}
3. Circle the answer. 1-Octanol is insoluble in water because: (a) it is a gas at room temperature; (b) the OH group is nonpolar; (c) alcohols do not dissolve in water; or (d) the molecule contains a long, nonpolar hydrocarbon “tail.”

   Correct answer is d.

4. The diol shown is nontoxic and used as a moisturizer in pharmaceuticals. It is detoxified in the liver by complete oxidation to pyruvic acid, which is an intermediate in metabolism. Which of the following structures is the likely structure of pyruvic acid? Explain.
   {13798_PreLabAnswers_Figure_12}
   Correct answer is d. 2° OH group was oxidized to ketone. 1° OH group was oxidized to carboxylic acid.
5. Phenols are weak acids and can be dissolved in water by neutralization with a base. Complete the following equation for the neutralization reaction of o-phenylphenol and draw the structure of its conjugate base.
   {13798_PreLabAnswers_Figure_13}

Sample Data

Answers to Questions

1. Compare the solubility of ethanol, 2-propanol, 2-methyl-2-propanol, and cyclohexanol in water. Explain any differences and write a general statement describing the solubility of alcohols in water.

   Ethanol, 2-propanol and 2-methyl-2-propanol were miscible with water. Cyclohexanol was only partially soluble— oily droplets were visible. Low-molecular weight alcohols (C1–C4) are soluble in water. As the number of carbon atoms increases, the solubility decreases; alcohols with > 8C are insoluble in water.

2. Which alcohol did not react with potassium chromate? Explain why based on its structure.

   2-Methyl-2-propanol did not react with potassium chromate. It is a tertiary alcohol, which cannot be oxidized.

3. Draw the structures of cyclohexanol and its likely oxidation product. Circle or label the hydrogen atoms that are “lost” when cyclohexanol is oxidized.
   {13798_Answers_Figure_14}
4. Consider the structures of compounds 1–3 shown. Which compounds would be expected to react with (a) cerium(IV) nitrate and (b) iron(III) chloride, respectively? Explain.
   {13798_Answers_Figure_15}
   1. 1 and 3 are alcohols—they will react with Ce(IV) ions.
   2. 2 is a phenol, which reacts with Fe(III) ions.
5. (a) Write a chemical equation for and draw the structure of the product obtained when benzaldehyde reacts with Tollens’ reagent. (b) Identify the functional group in the product and explain how you can determine, based on its molecular formula, that this product results from oxidation of benzaldehyde.
   1. {13798_Answers_Figure_16}
   2. The oxidation product is a carboxylic acid. Conversion of benzaldehyde to benzoic acid involves the gain of one oxygen atom in the molecular formula. Oxidation occurs when an organic compound either loses two H atoms or gains one O atom.
6. Compare the boiling point data for ethanol, its isomer, dimethyl ether, and two other compounds having similar molar masses. Explain the trend based on the types and strength of intermolecular forces.

   The boiling point of ethyl alcohol is 100 degrees (°C) higher than other compounds in this list. The difference is due to hydrogen bonding among alcohol molecules. Hydrogen bonding is the strongest type of intermolecular force, and the boiling point of a liquid increases as the strength of intermolecular forces increases. Propane is a hydrocarbon and has only very weak London dispersion forces between molecules; it has the lowest boiling point. Both methyl chloride and dimethyl ether are polar molecules characterized by somewhat stronger dipole-dipole forces between molecules.

7. Complete the following flow chart for the qualitative analysis of the natural products tested in this lab. Fill in the boxes with the name(s) of the compounds that gave positive and negative results, respectively, with the indicated reagents.
   {13798_Answers_Figure_18}
8. Match each natural product with its structure (a−c) based on the flow chart analysis completed above.

   Cinnamon oil ___b___ Eugenol ___c___ Geraniol ___a___

   {13798_Answers_Figure_19}

Introduction

Many important biological molecules incorporate an alcohol functional group. Oxidation of alcohols to carbonyl compounds is also an essential reaction in metabolism and other biochemical processes. The physical and chemical properties of alcohols and their oxidation products can be used to help identify the structures of natural products.

Concepts

• Alcohols and phenols
• Aldehydes and ketones
• Hydrogen bonding
• Oxidation and reduction
• Classification of alcohols
• Natural products

Background

The alcohol functional group consists of an OH group attached to a hydrocarbon skeleton. Oxidation of an alcohol results in the loss of two hydrogen atoms and conversion to a carbonyl compound, which contains the C=O functional group. The general structures of four classes of compounds within these functional group categories are shown in Figure 1, where R and R′ represent any alkyl group (chain or ring). Attachment of the OH group to a benzene or other aromatic ring distinguishes a phenol from an aliphatic alcohol, while carbonyl compounds are classified as either aldehydes or ketones.

The word “alcohol” is associated in common usage with ethyl alcohol, a specific—and most well-known—member of the general class of compounds. Ethyl alcohol, whose proper name is ethanol, is the familiar “grain alcohol” obtained by the fermentation of fruits and grains. The formula of ethanol is CH₃CH₂OH. With archeological and historical evidence for wine-making going back more than 5000 years and extending across many cultures, the fermentation of sugar to make ethanol (Equation 1) is one of the first chemical reactions used by humans. Beer or wine produced by fermentation contains a maximum alcohol concentration of 12–15% since yeast cells cannot survive higher concentrations. Distillation is used to increase the alcohol content to 20–50% in distilled beverages such as whiskey, gin, rum, etc. Ethanol is also an important solvent in pharmaceuticals, perfumes, flavorings, etc. The structures of five common alcohols are shown in Figure 2. Methanol, CH₃OH, is the simplest alcohol. It is sometimes called “wood alcohol” because it can be produced by the pyrolysis of wood. Methanol is a poisonous, flammable liquid, capable of causing blindness or death if taken internally. It is used as a fuel in race cars and is an important industrial solvent. Isopropyl alcohol, CH₃CH(OH)CH₃, is available commercially as “rubbing alcohol,” a common disinfectant that is a 70% solution with water. The systematic name for isopropyl alcohol is 2-propanol. Ethylene glycol, HOCH₂CH₂OH, is an example of a diol with two OH groups. It is the main ingredient in permanent antifreeze and is also the starting material for the preparation of polyester. The properties of ethylene glycol that make it ideal for use as an antifreeze include its complete miscibility with water as well as low freezing point and high boiling point. It is also toxic, however, and a dangerous household poison, especially for pets. The simplest organic compound with three OH groups is glycerol, HOCH₂—CH(OH)—CH₂OH, also known as glycerin. Glycerol is a smooth, syrupy, sweet liquid obtained as a byproduct of processing animal and vegetable fats to make soap. The presence of three OH groups makes glycerol extremely hygroscopic. It is an excellent moisturizer and is widely used as an emollient in cosmetics.

Structurally, alcohols may be considered derivatives of water (H₂O) in which a hydrogen atom is replaced by a hydrocarbon or alkyl group. As in water, the O—H bond in an alcohol is highly polar and capable of forming strong intermolecular hydrogen bonds. Hydrogen bonding between alcohol molecules is responsible for the relatively high boiling points of alcohols compared to other, similar-size molecules. The solubility of alcohols in water is also greater than that of other functional groups due to hydrogen bonding between alcohol and water molecules. Alcohols containing 1−3 carbon atoms are miscible with water, while C4–C7 alcohols are partially or sparingly soluble. As the number of carbon atoms increases, the influence of the nonpolar or hydrophobic hydrocarbon chain dominates the hydrophilic effect of the OH group, and > C8 alcohols are insoluble in water.

Alcohols are classified as primary, secondary or tertiary based on the number of carbon atoms attached to the carbon atom that bears the OH group (see Figure 3). This classification system is useful for predicting and explaining the chemical reactions of different alcohols and the structures of their oxidation products. Alcohols and carbonyl compounds are related by oxidation and reduction (see Figure 4). The loss of electrons accompanying oxidation of an organic compound is not easy to identify. Oxidation of an organic compound is more easily recognized by considering the formulas of the reactants and products. Oxidation occurs when an organic compound loses two hydrogen atoms or gains an oxygen atom. Ethanol (CH₃CH₂OH) is thus oxidized to ethanal (CH₃CHO) via the loss of two hydrogen atoms, one from the hydroxyl group and a second from the adjacent carbon atom. The C—O single bond is transformed into a C=O double bond in the process. Reaction of an alcohol with potassium chromate (K₂CrO₄), a strong oxidizing agent, provides a convenient qualitative test for classifying alcohols. Primary alcohols are oxidized to aldehydes, secondary alcohols are oxidized to ketones, and tertiary alcohols do not react. Observations for a positive test are a color change from orange (CrO₄^2–) to green (Cr³⁺). See Equations 2–4. A similar reaction is applied forensically in breathalyzer tests to determine blood alcohol levels. The intensity of the green color due to Cr³⁺ produced by breathing into a tube can be measured and related to the blood alcohol concentration because the vapor pressure of alcohol in exhaled air is proportional to the amount of alcohol in the blood. Oxidation of alcohols is physiologically important and a common biochemical pathway. Ethanol is metabolized and converted to ethanal in the liver. Accumulation of ethanal leads to acute, short-term effects, such as a hangover, and to chronic disease, including cirrhosis and liver cancer. The role of alcohol oxidation in metabolism is illustrated by the conversion of malate to oxaloacetate in the last step of the citric acid or Krebs cycle (Equation 5). (Oxaloacetate reacts further with acetyl coenzyme A to restart the cycle.) Phenol and many natural and synthetic phenol derivatives are common disinfectants and antiseptic agents (see Figure 4). They are also important antioxidants whose function is to prevent the oxidation of organic biological molecules. Vitamin E, for example, protects lung membranes from oxidative damage due to exposure to air pollutants such as smog and ozone. The synthetic phenol derivative BHT is commonly added to baked goods and other processed foods to prevent spoilage due to air oxidation. It is interesting to note that antioxidants work because they are themselves very easily oxidized compounds. Alcohols and phenols can be differentiated and identified by means of qualitative color tests with Ce(IV) and Fe(III) solutions, respectively. Alcohols react with cerium(IV) ammonium nitrate to form red or brown complex ions (Equation 6). Phenols react with iron(III) chloride to give red, blue or purple complex ions (Equation 7). Carbonyl compounds include two functional group classes, aldehydes and ketones, as shown below for the C₄H₈O isomers butanal, an aldehyde, and butanone, a ketone. The C=O group in an aldehyde is always found at the beginning of a chain of carbon atoms, while in a ketone, the carbonyl group occurs between two carbon atoms. 2-Pentanone and 3-pentanone are examples of isomeric ketones having the formula C₅H₁₀O. Aldehydes and ketones can be distinguished by means of a qualitative color test with Schiff’s reagent, which contains an indicator dye in a saturated solution of sulfur dioxide. The presence of sulfur dioxide renders the dye colorless and inactive. When an aldehyde is added to Schiff’s reagent, it reacts with the SO₂ and restores the deep purple color of the dye. Aldehydes and ketones also differ in their ability to be further oxidized. Aldehydes are easily oxidized by mild oxidizing agents, such as Cu²⁺ or Ag⁺ ions, to give carboxylic acids (RCO₂H). Ketones do not undergo further oxidation under these conditions. Equation 8 summarizes the reaction of an aldehyde with Ag⁺ ions in Tollens’ reagent. A positive Tollens’ test will result in the appearance of a gray-black precipitate of silver metal. In the classic Tollens’ test, the silver plates outs or deposits on the walls of the test tube as a beautiful silver mirror.

Experiment Overview

The purpose of this activity is to explore the physical and chemical properties of alcohols, phenols, aldehydes and ketones. The results of these tests will be used in a qualitative analysis scheme to identify the functional groups and structures of three natural products found in essential plant oils. The compounds to be tested and their functional group assignments are shown in Table 1.

Materials

Prelab Questions

1. The systematic names of alcohols are derived by adding the functional group ending -ol to the root name for the longest continuous carbon chain that contains the OH group. The carbon atom bearing the OH group is assigned the lower possible number and substituents are named and numbered using the same rules that apply to alkanes, alkenes, etc. Provide the systematic name for the compounds shown below.
   {13798_PreLab_Figure_7}
2. Draw the Lewis structure of a methanol molecule, including any lone pair(s) of electrons, and show by means of dashed lines the hydrogen bonds that can form between methanol and three water molecules.
3. Circle the answer. 1-Octanol is insoluble in water because: (a) it is a gas at room temperature; (b) the OH group is nonpolar; (c) alcohols do not dissolve in water; or (d) the molecule contains a long, nonpolar hydrocarbon “tail.”
4. The diol shown is nontoxic and used as a moisturizer in pharmaceuticals. It is detoxified in the liver by complete oxidation to pyruvic acid, which is an intermediate in metabolism. Which of the following structures is the likely structure of pyruvic acid? Explain.
   {13798_PreLab_Figure_8}
5. Phenols are weak acids and can be dissolved in water by neutralization with a base. Complete the following equation for the neutralization reaction of o-phenylphenol and draw the structure of its conjugate base.
   {13798_PreLab_Figure_9}

Safety Precautions

Carry out all procedures in an operating fume hood. Acetaldehyde, acetone, ethanol and 2-propanol are highly flammable liquids and vapors. Keep away from heat, sparks and open flames. Tollens’ reagent contains silver nitrate in a highly basic solution. It is corrosive to skin and eyes and will stain skin and clothing. Leftover mixtures containing Tollens’ reagent may form potentially explosive materials if left standing and allowed to dry. Follow the instructor’s directions for disposing of the leftover Tollens’ reagent immediately after use. Rinse with copious amounts of water into a container for disposal of the silver waste. Cerium(IV) nitrate and potassium chromate solutions contain acid and are corrosive to skin and eyes. Iron(III) chloride and salicylic acid may cause serious eye irritation. Avoid contact of all chemicals with eyes and skin. Organic liquids are volatile solvents and may cause drowsiness or respiratory tract irritation if inhaled. Avoid breathing mist, vapors or spray. Acetaldehyde and potassium chromate solutions are suspected carcinogens and/or genetic and reproductive hazards that may damage an unborn child. Work with these compounds in an operating fume hood only and do not use them if you are pregnant. Wear chemical splash goggles, chemical-resistant gloves and a lab coat or chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Properties of Alcohols

1. Obtain 1 mL each of the following compounds in clean, dry test tubes (1−4).
   {13798_Procedure_Table_2}
2. Add 10 drops distilled water to each test tube 1–4, and observe the appearance of each mixture. Which compounds are soluble in water?
3. Pour the contents of the test tubes into an appropriately labeled waste beaker. Rinse the test tubes with acetone and wipe clean with a paper towel. Refill test tubes 1–4 as shown in step 1.
4. Observe the color of potassium chromate solution and add 2 mL of this oxidizing agent to each test tube 1–4. Stopper the tubes and observe any changes in the color and appearance of each mixture. Allow 3–5 minutes for complete reaction. Which alcohols reacted with potassium chromate?
5. Pour the contents of the test tubes into an appropriately labeled beaker for heavy metal waste. Rinse the test tubes with acetone and wipe clean with a paper towel.

Color Tests for Alcohols and Phenols

1. Set up six clean and dry test tubes in a test tube rack.
2. Observe the color of cerium(IV) nitrate solution and add 2 mL of this reagent to three test tubes (1–3).
3. Observe the color of iron(III) chloride solution and add 2 mL of this reagent to the second set of three test tubes (4–6).
4. Add 5 drops of the alcohol or phenol to be tested to the appropriately labeled test tube, as shown below.
   {13798_Procedure_Table_3}
5. Observe any changes in the color and appearance of each mixture. Which compounds gave positive test results with Ce(IV) ions? With Fe(III) ions?
6. Pour the contents of the test tubes into an appropriately labeled waste beaker. Rinse the test tubes with acetone and wipe clean with a paper towel.

Qualitative Tests for Aldehydes

1. Set up three clean and dry test tubes in a test tube rack and label them 1−3. Add 1 mL of Tollens’ reagent to each test tube.
2. Add 1−2 drops of the aldehyde or ketone to be tested to the appropriately labeled test tube, as shown below. Record observations. Which compounds were oxidized by Ag⁺ ions?
   {13798_Procedure_Table_4}
3. Immediately rinse the contents of the test tubes with water into an appropriately labeled container. Do NOT allow the Tollens’ reagent or leftover test mixtures to dry out.
4. Wash and rinse the test tubes. Test tubes with a “silver mirror” may need to be disposed or discarded, as removing silver would require treatment with nitric acid.
5. Relabel three clean test tubes 1−3, and add 2 mL of Schiff’s reagent to each test tube. .
6. Add 3−5 drops of the aldehyde or ketone to be tested to the appropriately labeled test tube, as shown below. Record observations. Which compound(s) reacted with Schiff’s reagent?
   {13798_Procedure_Table_5}
7. Pour the contents of the test tubes into an appropriate waste container.

Analysis of Natural Products

1. Obtain about 2 mL each of three natural product “unknowns” (cinnamon oil, eugenol and geraniol) in separate containers.
2. Set up six clean test tubes in a test tube rack.
3. Test each unknown with iron(III) chloride (2 mL of FeCl₃ solution and 5 drops of the natural product).
4. Which natural product(s) gave a positive test result with Fe³⁺ ions? Fill in the flow chart in the Laboratory Report.
5. Test any remaining unknowns that did NOT react with Fe³⁺ using Schiff’s reagent (2 mL of Schiff’s reagent and 3−5 drops of natural product).
6. Record observations and identify which natural product(s) gave a positive test result with Schiff’s reagent.
7. Confirm the identity of the remaining unknown by testing with potassium chromate. (Add 2 mL of potassium chromate solution to 1 mL of natural product.)
8. Pour the contents of the test tubes into appropriately labeled waste beakers, as directed by the instructor.

Student Worksheet PDF

13798_Student1.pdf