qualitative organic analysis lab

1. Why is it important to have
clean test tubes before running a test?
Before which tests should acetone not be used to clean the test tubes?

2. Why run solubility tests before running the functional group classification tests?

3. Determine the functional group present in these unknown:
(a) Unknown A is soluble in water and gives bubbles with5% NaHCO3.
(b) Unknown B is insoluble in water, insoluble in 5% NaOH, but soluble in 5% HCl.

(c) Unknown C is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, soluble with a color change in conc. H2SO4, and decolorizes both KMnO4 (aq) and bromine in cyclohexane.

(d) Unknown D is soluble in water, does not produce bubbles with 5% NaHCO3, gives a precipitate with 2,4-DNP, and gives a hsia color with the Schiff test.

4. In each of the following cases, describe the next test you would perform.
(a) Unknown X is insoluble in water, 5% NaOH, 5% HCl, and conc. H2SO4.

(b) Unknown Y is insoluble in water, soluble in 5% NaOH, and insoluble in 5% NaHCO3.

(c) Unknown Z is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, and soluble in conc. H2SO4.


5. You suspect that your unknown contains halogen, so you perform the silver nitrate in ethanol test and the sodium iodide in acetone test, both of which are negative. Do these results prove that your compound does not contain a halogen? Briefly explain.

1. Why is it important to have clean test tubes before running a test?

Before which tests should acetone not be used to clean the test tubes?
Due to contamination from past experiments interfering with any of the reactions. Acetone should not be used to clean the test tubes before the Jones test.

2. Why run solubility tests before running the functional group classification tests?
Solubility tests helps to determine the size and polarity of an unknown compound and the presence of basic or acidic functional groups; it therefore helps limit the possible functional group. Thus not all of the classification tests are needed to be carried out, just specific ones needed to rule out the specific functional group for a compound. This helps save time and materials.

3. Determine the functional group present in these unknown:
(a) Unknown A is soluble in water and gives bubbles with5% NaHCO3. – carboxylic acid
(b) Unknown B is insoluble in water, insoluble in 5% NaOH, but soluble in 5% HCl.- amine

(c) Unknown C is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, soluble with a color change in conc. H2SO4, and decolorizes both KMnO4 (aq) and bromine in cyclohexane. – alkenes

(d) Unknown D is soluble in water, does not produce bubbles with 5% NaHCO3, gives a precipitate with 2,4-DNP, and gives a hsia color with the Schiff test. – aldehydes

4. In each of the following cases, describe the next test you would perform.
(a) Unknown X is insoluble in water, 5% NaOH, 5% HCl, and conc. H2SO4.
- Performing the Silver Nitrate in Ethanol Test for 2° and 3° Alkyl Halides
Place 1 mL of 2% AgNO3 in ethanol into a small test tube.
For liquid samples, add 2 drops of sample to the 2% AgNO3. Tap the tube with your finger to mix or stir gently with a glass stirring rod. For solid samples, place 30 mg of solid into a test tube. Add 5 drops of ethanol. Add this ethanol solution to the 2% AgNO3 in ethanol. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Note and record whether or not a precipitate forms. An immediate precipitate indicates a tertiary, allylic, or benzylic halide.
Performing the Sodium Iodide in Acetone Test for 1° and 2° Alkyl Halides
Place exactly 1.0 mL of NaI in acetone into a small test tube. Add 3 drops of a liquid sample. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Allow the tube to stand 3-6 min at room temperature. A white precipitate indicates a primary, allylic, or benzylic halide.
(b) Unknown Y is insoluble in water, soluble in 5% NaOH, and insoluble in 5% NaHCO3.
Performing the Bromine in Water Test for Phenols
Place 1 mL of 95% ethanol into a small test tube. Add 5 drops of a liquid sample or about 30 mg of a solid. Add a drop of water. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Add 1 drop of Br2/H2O. Tap the tube with your finger to mix or stir gently with a glass stirring rod. The disappearance of the orange color will indicate a phenol.
(c) Unknown Z is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, and soluble in conc. H2SO4.
Conduct classification test for an alkene, an alcohol, an aldehyde, and a ketone.
Perform the Bromine in Cyclohexane or the Potassium Permanganate Test for Alkenes. Place 1 mL of cyclohexane in a small test tube. Add 3 drops of Br2/H2O. Mix until the bromine color appears in the top cyclohexane layer.
For liquid samples, add 2 drops of sample to the Br2/H2O. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Note and record whether or not the orange color disappears.
For solid samples, place 30 mg of solid into a test tube. Add 5 drops of acetone. Add the acetone solution to the Br2/H2O. Tap the tube with your finger to mix or stir gently with a glass stirring rod. If the orange color disappears quickly, the sample may be an alkene.

Performing the Potassium Permanganate Test for Alkenes If your sample is water soluble, place 1-2 mL of water into a small test tube. If your sample is water-insoluble, place 1-2 mL of 95% alcohol into a small test tube.
Add 2 drops of a liquid sample or about 30 mg of a solid sample. Add 2 drops of 1% KMnO4.
Tap the tube with your finger to mix or stir gently with a glass stirring rod. Let the mixture stand 10-20 s. If the purple color disappears and a brown color or precipitate appears, the compound may be an alkene.

If it’s not an alkene Perform the TCICA Test for Alcohols- Place 0.5 mL of the TCICA test solution into a small test tube. Add 1 drop of 5% HCl. Tap the tube with your finger to mix or stir gently with a glass stirring rod.
For liquid samples, add 1 drop of the sample. Tap the tube with your finger to mix or stir gently with a glass stirring rod.
For solid samples, dissolve about 20 mg of solid in 1-2 drops of acetonitrile. Add this solution to the TCICA/HCl solution. Note and record whether or not a precipitate forms. The formation of a precipitate within one min indicates a secondary alcohol; the formation of a precipitate between 3-20 min indicates a primary alcohol.
And if its not an alcohol it has to be a aldehyde or keton, so it would be positive for the2,4-DNP Test for Aldehydes and Ketones-
For liquid samples, place 1 drop of sample into a clean, dry test tube. Add up to 20 drops of 2,4-DNP solution. Tap the tube with your finger to mix or stir gently with a glass stirring rod.
For solid samples, add about 30 mg of solid into a clean, dry test tube. Add 0.5 mL of ethanol. Tap the tube with your finger to mix or stir gently with a glass stirring rod. If the unknown does not dissolve, prepare a warm-water bath by placing 175-200 mL of tap water into a 250-mL beaker. Use a hot plate toheat the water to 40°C. Place the test tube into a warm-water bath and swirl the tube until the unknown is dissolved. Cool the solution to room temperature. Add up to 20 drops of 2,4-DNP solution. Tap the tube with your finger to mix or stir gently with a glass stirring rod. An immediate, brightly colored precipitate indicates an aldehyde or ketone.

5. You suspect that your unknown contains halogen, so you perform the silver nitrate in ethanol test and the sodium iodide in acetone test, both of which are negative. Do these results prove that your compound does not contain a halogen? Briefly explain.

No it doesn’t. There may not be halide ions but halogens found in another group. And they are only negative for reactions that can undergo an SN1 (ethanol) or SN2 (acetone) reaction. Bromobenzene will not undergo either reaction, will give a negative result, and contain a halogen.

1. It is important to have clean test tubes before running tests because any contaminants or residue from previous experiments can interfere with the results and affect the accuracy of the analysis. Acetone should not be used to clean test tubes before tests that involve organic compounds that are soluble in acetone, as it may dissolve or contaminate the compound being tested.

2. Solubility tests are run before functional group classification tests because they help determine the solubility characteristics of the unknown compound. Solubility can provide valuable information about the chemical nature of the compound and guide the subsequent tests. By identifying whether the compound is soluble or insoluble in different solvents, we can narrow down the possible functional groups present.

3.
(a) Unknown A is soluble in water and gives bubbles with 5% NaHCO3. This indicates the presence of a carboxylic acid functional group.
(b) Unknown B is insoluble in water, insoluble in 5% NaOH, but soluble in 5% HCl. This suggests the presence of a phenol or an amine functional group.
(c) Unknown C is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, soluble with a color change in conc. H2SO4, and decolorizes both KMnO4(aq) and bromine in cyclohexane. This indicates the presence of an unsaturated hydrocarbon, possibly an alkene or an alkyne.
(d) Unknown D is soluble in water, does not produce bubbles with 5% NaHCO3, gives a precipitate with 2,4-DNP, and gives a hsia color with the Schiff test. This suggests the presence of an aldehyde or a ketone functional group.

4.
(a) For Unknown X, the next test that can be performed is a flame test to check for the presence of a metal ion.
(b) For Unknown Y, the next test to perform could be a test for the presence of an acid functional group using litmus paper.
(c) For Unknown Z, the next test that can be performed is a test for the presence of an aromatic compound using the benzene test.

5. The negative results from the silver nitrate in ethanol test and sodium iodide in acetone test do not conclusively prove that the compound does not contain a halogen. It is possible that the concentration of halogen in the compound is too low to produce a positive result in the tests. To confirm the absence of halogens definitively, further tests specifically targeting halogens would need to be conducted.

1. It is important to have clean test tubes before running a test in qualitative organic analysis because any residue or impurities left in the test tubes can interfere with the accuracy of the tests. Contaminants in the test tubes can lead to false positive or false negative results. Acetone should not be used to clean the test tubes before performing certain tests, such as tests involving organic compounds that are sensitive to acetone or tests where acetone can react with the compounds being tested.

2. Solubility tests are typically performed before running functional group classification tests in qualitative organic analysis because the solubility of a compound can provide initial information about its possible functional groups. Different functional groups have characteristic solubility properties in different solvents. By determining the solubility of the unknown compound in various solvents, we can narrow down the possible functional groups present and choose appropriate classification tests.

3.
(a) Unknown A is soluble in water and gives bubbles with 5% NaHCO3. This indicates the presence of a carboxylic acid functional group.
(b) Unknown B is insoluble in water, insoluble in 5% NaOH, but soluble in 5% HCl. This suggests the presence of an acidic functional group, such as an amine or phenol.
(c) Unknown C is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, soluble with a color change in conc. H2SO4, and decolorizes both KMnO4 (aq) and bromine in cyclohexane. These characteristics suggest the presence of an unsaturated carbon-carbon bond, such as an alkene or alkyne.
(d) Unknown D is soluble in water, does not produce bubbles with 5% NaHCO3, gives a precipitate with 2,4-DNP, and gives a hsia color with the Schiff test. These observations indicate the presence of a carbonyl group, such as an aldehyde or ketone.

4.
(a) For Unknown X that is insoluble in water, 5% NaOH, 5% HCl, and conc. H2SO4, the next test to perform could be a test for insoluble organic compounds, such as a test for an insoluble organic pigment or a test for an inorganic compound that might be present.
(b) For Unknown Y that is insoluble in water, soluble in 5% NaOH, and insoluble in 5% NaHCO3, the next test to perform could be a test for acidic functional groups, such as a test for carboxylic acids.
(c) For Unknown Z that is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, and soluble in conc. H2SO4, the next test to perform could be a test for sulfur-containing functional groups, such as a test for sulfides or thiols.

5. Negative results from the silver nitrate in ethanol test and the sodium iodide in acetone test do not fully prove that the compound does not contain a halogen. These tests may not detect certain halogen compounds due to their specific reaction conditions or limitations. To definitively determine the absence of halogen, further tests specifically designed to detect halogen atoms should be performed.

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