LAB 4 - ALDEHYDES AND KETONES
- Page ID
- 506281
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The purpose of this experiment is to:
- Draw structures of aldehydes and ketones
- Name aldehydes and ketones
- Explore the physical properties and reactions of aldehydes and ketones
- Perform chemical tests on aldehydes and ketones
INTRODUCTION
Aldehydes are organic compounds that contain a carbonyl group (C=O) bonded to a hydrogen atom, whereas ketones have a carbonyl group located between two carbon atoms. As you will observe in this experiment, aldehydes and ketones exhibit similar physical and chemical properties. Like other functional groups you have previously studied, chemical tests can be used to identify aldehydes and ketones. Aldehydes react with Benedict’s reagent, a solution containing copper(II) ions, to produce carboxylic acids, as illustrated by the equation below:
During this reaction, copper(II) ions are reduced to copper(I) ions, leading to the formation of a red-orange precipitate. This indicates a positive test result for Benedict’s reagent. A negative test result is shown by the persistence of a blue solution, due to the presence of unreacted copper(II) ions. Since ketones do not undergo oxidation with common laboratory reagents, they will yield a negative test result with Benedict’s reagent.
The iodoform test is a chemical procedure primarily used for methyl ketones, which have a methyl group attached to the carbonyl group. Consider the reaction between 2-hexanone and the iodoform reagent:
During the reaction, the red color of iodine disappears, forming a yellow solution or precipitate (due to the presence of iodoform). This indicates a positive test result. In contrast, if the red color of iodine remains, it signifies a negative test result.
1) Wear chemical splash goggles while working on this experiment.
2) Handle all reagents and perform all parts of this experiment under a working fume hood.
3) Gloves are provided, and we encourage you to wear them.
4) Be cautious when handling hot glassware after performing the simple distillation.
5) Dispose of all waste in the appropriate container and clean all equipment and your work area when finished.
CHEMICALS AND EQUIPMENT NEEDED
CHEMICALS |
CHEMICALS |
CHEMICALS |
EQUIPMENT |
EQUIPMENT |
|---|---|---|---|---|
|
Propanal |
Cyclohexanone |
Iodoform Reagent* |
Styrofoam Cup |
7 small or medium-sized Test Tubes |
|
Butanal |
Unknown aldehyde or ketone |
Benedict’s Reagent* |
Thermometer |
Test Tube Rack |
|
Benzaldehyde |
Solid NaBr |
10% NaOH solution (or similar concentration) |
Watch glass |
400 mL Beaker |
|
Acetone |
Solid NaI |
Non-halogenated organic waste container |
Hot Plate |
Stirring Rod |
|
2-butanone |
Solid NaCl |
Halogenated organic waste container |
600 mL Beaker |
Spatula |
|
Water |
Isopropyl alcohol |
- | - | - |
EXPERIMENTAL PROCEDURE
Part A: Structures and Solubility
1) Draw Lewis, condensed, or line-bond structures for the compounds used in this experiment.
Propanal, butanal, benzaldehyde, acetone, 2-butanone, cyclohexanone
2) Obtain 7 test tubes. Add the following reagents:
Test tube 1: 1 mL of Propanal and 1 mL of water.
Test tube 2: 1 mL of Butanal and 1 mL of water.
Test tube 3: 1 mL of Benzaldehyde and 1 mL of water.
Test tube 4: 1 mL of Acetone and 1 mL of water.
Test tube 5: 1 mL of 2-butanone and 1 mL of water.
Test tube 6: 1 mL of Cyclohexanone and 1 mL of water.
Test tube 7: 1 mL of Unknown and 1 mL of water.
3) Thoroughly mix the contents of each test tube and record your observations.
4) Pour the contents of each test tube into the non-halogenated organic waste container. Clean and dry the test tubes, then store them for later use.
Part B: Acetone as a Solvent
1) Obtain three small or medium-sized test tubes. Add the following reagents as indicated.
Test tube 1: a small scoop of solid NaCl and 1 mL of acetone.
Test tube 2: a small scoop of solid NaBr and 1 mL of acetone.
Test tube 3: a small scoop of solid NaI and 1 mL of acetone.
Note: Clean and dry the spatula between uses to avoid cross-contamination of the solid bottles.
2) Thoroughly mix the contents of each test tube and record your observations.
3) Pour the contents of each test tube into the halogenated organic waste container. Wash and dry the test tubes, then save them for future use.
4) Fill a 400 mL beaker with 10 mL of acetone. Add a Styrofoam cup containing acetone to the beaker and record your observations. (This can also be done as a demonstration by the instructor.)
5) Pour the contents of the beaker into the non-halogenated organic waste container. Clean and dry the beaker.
Part C: Volatility of Acetone
Get a watch glass. To separate the sides of the watch glass, add five drops of acetone and five drops of isopropyl alcohol. Record how long it takes for each solvent to evaporate completely.
Part D: Iodoform Test
1) Obtain seven small or medium-sized test tubes. Add the following reagents:
Test tube 1: 10 drops of Propanal, 2 mL of water, and 10 drops of 10% NaOH.
Test tube 2: 10 drops of Butanal, 2 mL of water, and 10 drops of 10% NaOH.
Test tube 3: 10 drops of Benzaldehyde, 2 mL of water, and 10 drops of 10% NaOH.
Test tube 4: 10 drops of Acetone, 2 mL of water, and 10 drops of 10% NaOH.
Test tube 5: 10 drops of 2-butanone, 2 mL of water, and 10 drops of 10% NaOH.
Test tube 6: Ten drops of cyclohexanone, 2 mL of water, and ten drops of 10% NaOH.
Test tube 7: 10 drops of Unknown, 2 mL of water, and 10 drops of 10% NaOH
2) Obtain a hot plate and a 600 mL beaker, filling it three-quarters with water. Place the test tubes in the beaker with water, and set the beaker on the hot plate. Heat the water bath to a temperature of no more than 55 °C. You can check the temperature with a thermometer.
3) Place the test tubes in the water bath and add 20 drops of the iodoform reagent. Mix using a glass stirring rod. After 2 minutes, document your observations.
4) Pour the contents of each test tube into the halogenated organic waste container. Rinse and dry the test tubes, then set them aside for later use.
5) Save the water bath for part E.
Part E: Benedict’s Test
1) Obtain seven small or medium test tubes. Add the following reagents:
Test tube 1: 10 drops of Propanal and 2 mL of Benedict’s reagent.
Test tube 2: 10 drops of butanal and 2 mL of Benedict’s reagent.
Test tube 3: 10 drops of benzaldehyde and 2 mL of Benedict’s reagent.
Test tube 4: 10 drops of acetone and 2 mL of Benedict’s reagent.
Test tube 5: 10 drops of 2-butanone and 2 mL of Benedict’s reagent.
Test tube 6: 10 drops of cyclohexanone and 2 mL of Benedict’s reagent.
Test tube 7: 10 drops of unknown and 2 mL of Benedict’s reagent.
2) Mix the contents of each test tube using a glass stirring rod, and then place the test tubes in the water bath used for part D. Heat it to a boil. Once the water starts to boil, let the test tube sit in the water bath for 5 minutes. Record your observations after 5 minutes.
3) Pour the contents of each test tube into the non-halogenated organic waste container. Disassemble the water bath, then wash and dry the test tubes.
PRE-LAB QUESTIONS
Name ____________________________________
1) Provide a reasonable name for the following compounds.
2) Draw structures for the following compounds.
Part A: 2,2-dimethyl-3-hexanone
Part B: 2-bromocyclohexanone
Part C: 2-ethylpentanal
Part D: hexanal
Part E: 5-chloro-2,2-dimethylcyclopentanone
3) Are aldehydes and ketones polar or nonpolar? What is the primary intermolecular force present in these compounds?
4) Predict the major products from each of the following reactions.
DATA AND OBSERVATIONS
Name _________________________Lab Partner(s) ______________________________
Part A: Structures and Solubility
Compound |
Structure |
Soluble or Insoluble in Water? |
|---|---|---|
|
Propanal |
||
|
Butanal |
||
|
Benzaldehyde |
||
|
Acetone |
||
|
2-butanone |
||
|
Cyclohexanone |
||
|
Unknown |
X |
Part B: Acetone as a Solvent
Compound |
Soluble or Insoluble in Acetone? |
|---|---|
|
NaCl |
|
|
NaBr |
|
|
NaI |
|
Describe what happens when the Styrofoam cup is added to acetone.
Part C: Volatility of Acetone
Compound |
Primary Intermolecular Force |
The Time it Takes to Evaporate |
|---|---|---|
|
Isopropyl alcohol |
||
|
Acetone |
Parts D and E: Chemical Tests
Compound |
Results of the Iodoform Test |
Results of Benedict’s Test |
|---|---|---|
|
Propanal
|
|
|
|
Butanal
|
|
|
|
Benzaldehyde
|
|
|
|
Acetone
|
|
|
|
2-butanone
|
|
|
|
Cyclohexanone
|
|
|
|
Unknown
|
|
|
Analysis of Unknown:
Unknown letter or number:
Based on the results of the solubility, iodoform, and Benedict’s tests, identify your unknown as one of the six knowns.
POST-LAB QUESTIONS
1) Explain how certain aldehydes and ketones can dissolve in water.
2) The halide test in acetone is a chemical test for certain alkyl halides. Based on the result from part B of this experiment, which halogen (Cl, Br, or I) would best serve this purpose? Explain.
3) Explain the results of part C (volatility of acetone) in relation to intermolecular forces.
4) Write the major product for any reaction occurring in part E (Benedict’s test).
5) An unknown compound with the molecular formula C4H8O yielded the following results in four chemical tests.
Chemical Test |
Result |
|---|---|
|
Bromine Test |
Formation of a colorless solution |
|
Potassium Permanganate Test |
Formation of a brown solid |
|
Benedict’s Test |
Formation of blue solution |
|
Iodoform Test |
Formation of red solution |
Using only the results of these chemical tests, draw two possible structures for the unknown.
Please click here to access the Pre-Lab, Data Tables, and Post-Lab in Word or PDF format. Complete them and upload the lab report according to your instructor's instructions.
*Preparation of Reagents: To prepare the Iodoform reagent, dissolve 10 g of I2 and 20 g of KI in sufficient water to achieve a total volume of 100 mL. For Benedict’s reagent, dissolve 86 g of sodium citrate and 50 g of anhydrous sodium carbonate in 400 mL of warm water. Next, dissolve 8.6 g of copper(II) sulfate pentahydrate in 50 mL of water, then add this solution to the citrate/carbonate mixture. Add sufficient water to obtain a final volume of 500 mL.