Investigating Organic Functional Groups Cautions HCl and NaOH ...

Austin Peay State University Department of Chemistry Chem 1041 

Investigating Organic Functional Groups 

Cautions 

HCl and NaOH are corrosive and toxic 

Purpose 

In this lab you will use traditional chemical tests to identify a variety of functional groups in known chemicals. 

You will use those positive results to identify the functional groups present in an unknown compound. 

Introduction 

Chemists today are trained to use elaborate technologies and instrumentation to determine chemical structure 

and makeup. However, many years ago, these technologies were not yet available, and there were very few ways 

for chemists to determine the composition of any chemical. Chemists would use a series of tests to characterize 

the structure and makeup of a chemical. You will be doing some of these tests in this lab, in particular, ones that 

indicate functional groups present on a molecule. 

Functional groups can be defined as the parts of organic molecules that are prone to chemical reactions. 

Saturated hydrocarbons (carbon chain molecules with all single bonds and the maximum number of hydrogen 

atoms) are not especially susceptible to reactions, but chemicals that contain oxygen, nitrogen, halogens (Br, Cl, F, 

and I) and double or triple bonds between carbon atoms can readily react in specific conditions. Alkenes, alcohols, 

aldehyde, ketone, and alkyl halide compounds will be studied. 

Alkenes 

Alkenes are chemicals that contain a carbon-carbon double bond as the functional group. They react with the 

magenta-colored chemical potassium permanganate (KMnO 4 ) to product manganese dioxide (MnO 2 ), which is a 

brown solid. In other words, you can determine if a chemical has a double bond by adding KMnO 4 and looking for 

the development of the brown solid MnO 2 . 

Example 1: Oxidation of 1-butene by KMnO 4 

OH 

H 2 

C CH 

3 2 +4H 2 O + 2 KMnO 4 

3 

H 3 C C 

H 

H 3 C 

H 2 

C 

H 

C 

CH 2 

+2MnO 2 

+2KOH 

OH 

Alcohols 

An alcohol is any organic compound that has a hydroxyl functional group (-OH) bonded to a carbon atom, 

which is usually connected to other carbon or hydrogen atoms. Alcohols are oxidized with Jones reagent (chromic 

acid (H 2 CrO 4 ) and sulfuric acid (H 2 SO 4 )) to give a carbonyl (C=O) and a green chromium compound. Positive 

identification of an alcohol will be evident when the addition of chromic acid results in a green solution. This 

reaction is quick, working on the order of 2-3 seconds. Aldehydes also react with chromic acid to produce the 

green chromium compound, but the reaction takes a bit longer, 10-12 seconds or so. 

Revision S10 Page 1 of 7



Example 2: Reduction of 2-propanol (iso-propanol) 

H3 C 

H 

C 

CH 3 

H 2 CrO 4 

H3 C 

C 

CH 3 

+ 

H 2 CrO 3 + H 2 O 

OH 

O 

Ketones and Aldehydes 

Ketones and aldehydes both contain the same functional group, a carbon-oxygen double bond. In a ketone, 

the carbon atom is also attached to two other carbons. In an aldehyde, the carbon is bonded to another carbon 

and a hydrogen. Both ketones and aldehydes react with a chemical called 2,4-dinitrophenylhydrazine (2,4-DNPH) 

to form a yellow or orange solid within a few minutes. 

Example 3: Reaction of propanone (a ketone) with 2,4-DNPH 

NO 2 

H 3 C 

C 

CH 3 

+ 

H 

N 

NH 2 

NO 2 

H 

N 

N 

CH 3 

C 

CH3 

+H 2 O 

O 

O 2 N 

O 2 N 

2,4-DNPH 

Example 4: Reaction of propanal (an aldehyde) with 2,4-DNPH 

NO 2 

H 

C 

CH 3 

+ 

H 

N 

NH 2 

NO 2 

H 

N 

N 

CH 3 

C 

H 

+H 2 O 

O 

O 2 N 

O 2 N 

2,4-DNPH 

Alkyl Halides 

Alkyl halides are alkanes that have a halide ion (such as chloride or bromide) bonded to carbon in the usual 

place of a hydrogen atom. Halides in organic compounds can be identified by way of a Beilstein test. A copper 

wire is heated under a flame to from a layer of copper(II) oxide (CuO) on the wire. Dip the coated wire in your 

compound and then place under the flame. If a halide is present in the organic compound, it reacts with copper(II) 

to form a copper halide, which burns green in the flame. 

Example 5: Identification of methyl bromide by Beilstein test 

Cu(s) 

flame 

H 3 C Br 

CuO(s) CuBr 2 




Procedure 

Keep the resulting test tubes from your standard tests until the end of the experiment for comparison to your 

unknown compound. 

1. Testing for alkenes: Set up two test tubes in the test tube rack. In tube one, put in 4 drops of hexane. In 

tube two, put in 4 drops of pentene. Add 2 mL of ethanol to each tube. Add two drops of the 

permanganate solution, stopper, and shake (be careful you know which tube is which!) Record the results 

on the data sheet. 

2. Testing for alcohols: Set up two new test tubes in the test tube rack. In tube one, put in 1 drop of hexane, 

and in tube two put in one drop of ethanol. Add 1 mL of acetone to each tube followed by 1 drop of the 

chromic acid reagent. Gently swirl the tubes. Record the results on the data sheet. 

3. Testing for ketones: Set up two test tubes in the test tube rack. In tube one, put in 2 drops of hexane, and 

in tube two, put in 2 drops of acetone. Add 2 mL of ethanol to each tube followed by 3 mL of the 2,4-DNPH 

reagent. Stopper and shake well. Let the solution stand for up to 15 minutes. You can go onto the next 

test in this time. Record the results on the data sheet. 

4. Testing for aldehydes: You will be using two tests for aldehydes, the chromic acid test as well as the 2,4- 

DNPH test. Because you already know what the negative tests for these look like, you will only be doing 

the positive tests. Set up two test tubes in the test tube rack. In tube 1, put in 1 drop of hexanal, 1 mL of 

acetone, and 1 drop of chromic acid. Swirl the tube. In tube 2, put in 2 drops of hexanal, 2 mL of ethanol, 

and 3 mL of the 2,4-DNPH reagent. Stopper and shake the tube. Wait up to 15 minutes for a reaction in 

tube 2. Compare the tests to the positive and negative tests in 2 and 3 above. Record the results on the 

data sheet. 

5. Testing for alkyl halides: Take a small length of copper wire and brush it clean using the sand paper. Hold 

it over a flame for about 30 seconds. Take it out of the fire and let it cool down. Dip the wire in hexane and 

hold over the flame. Repeat the procedure using methylene chloride. Record the results on the data 

sheet. 

6. Testing your unknown: Obtain your unknown and perform the tests described in steps 1-5. Make careful 

observations and record your results on the data sheet. Compare to the results to those for the known 

chemicals to determine the functional groups present in your compound. 

Waste Disposal 

Collect all chemicals in the appropriate waste container. 

Clean-Up 

Wash all glassware with soap then rinse 3 times with tap water, and once with deionized water. 




Data Sheet 1 

Name: _______________________________ 

Lab Partner: ______________________________ 

Test Sample Observations 

Alkene Test 

Hexane 

(control) 

Propene 

Alcohol Test 

Hexane 

(control) 

Ethanol 

Ketone Test 

Hexane 

(control) 

Acetone 

Aldehyde Tests 

Reaction with 

Chromic acid 

Reaction with 

2,4-DNPH 

Alkyl Halide Test 

Hexane 

(control) 

Methylene 

Chloride 




Data Sheet 2 

Unknown Number: _______________________________________ 

Test 

Observations 

Positive 

(+) or 

Negative 

(-)? 

Alkyl Halide 

Test 

Aldehyde Test 

Ketone Test 

Alcohol Test 

Alkene Test 




Post-lab Assignment 

Name: ______________________________ 

1. Which functional groups are present in your unknown chemical? Explain your reasoning using the results 

of the tests performed on your unknown. 

2. Using what you have learned in this lab, is there a way to identify a chemical that has an alcohol and an 

aldehyde functional group on it? If yes, which tests would you use and why? 

3. Propose a way to identify a compound with both an aldehyde and a ketone functional group. Explain your 

answer. 




Pre-lab Assignment 

Name: _________________________________ 

1. Draw the Lewis-dot structures of the compounds listed below that you will be using in this lab. Circle and 

name the functional group. 

a) Hexane 

d) Ethanol 

b) Acetone 

e) Hexanal 

c) Propene 

f) Methylene chloride 

2. Name and circle the functional groups shown in the compounds below. Which test would you use for the 

following chemicals? 

CH 3 

a) 

H 3 C 

C 

C 

H 

H 2 

C 

CH 3 

CH 3 

b) 

H 

C 

CH 

CH 3 

O

Investigating Organic Functional Groups Cautions HCl and NaOH ...

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