chemistry

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.

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asked by Niah
  1. Do you honestly not know the answer to #1?
    Why don't you try answering these and let us respond?

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  2. 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.

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