OVHS The Aldehydes and Ketones Can Be Distinguished by Potassium Analysis

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Assignment: Qualitative Analysis of Functional Groups
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Assignment: Qualitative Analysis of
Functional Groups
Organic compounds can be classified based on the functional groups they contain.
These functional groups help determine a compound’s reactivity and physical
properties, such as boiling point and solubility.
In this lab assignment, you will identify organic compounds based on their reactivity
in six different tests, their solubility in water, and their boiling point. You will also
provide a possible IUPAC name for each unknown assigned to you.
Instructions
To complete this assignment, follow these steps:
1. Read the chart in the accordion panel below to familiarize yourself with the six
tests that you will virtually perform on your unknown substances. Make sure you
understand what a positive and negative result means for each test.
Chemical Tests Table
Test
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Result
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Assignment: Qualitative Analysis of Functional Groups
Test
Result
Cerric Nitrate Test
To determine the presence of alcohols
Reaction
A negative test (left)
and a positive test
(right)
Procedure
The unknown is added to an acidified cerric ammonium
nitrate solution (yellow).
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Assignment: Qualitative Analysis of Functional Groups
Test
Result
Chromic Acid Test
To determine the presence of primary and secondary
alcohols, and aldehydes
Reactions
Aldehydes and primary alcohols are oxidized to
carboxylic acids and while the Cr6+ ion in chromic acid is
reduced to Cr3+ (green).
A negative test (left)
and a positive test
(right)
Secondary alcohols are oxidized to ketones while the
Cr6+ ion is reduced to Cr3+ (green).
Procedure
A mixture of acetone and chromic acid solution (reddishorange) is added to the unknown solution.
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Assignment: Qualitative Analysis of Functional Groups
Test
Result
2,4-Dinitrophenylhydrazine Test
To determine the presence of aldehydes and ketones
Reaction
2,4-dinitrophenylhydrazine reacts with the carbonyl group
of aldehydes and ketones to form a precipitate.
A negative test (left)
and a positive test
(right)
Procedure
A mixture of 2,4-dinitrophenylhydrazine (orange solution)
and ethanol is added to the unknown solution. If no
positive test is observed (orange precipitate forms), than
a final observation is made after 15 minutes.
Iron Chloride Test
To determine the presence of phenols
Reaction
Phenols form a complex with the iron ions, creating a
colour change which varies from reddish brown to purple
to blue to dark green (depending on the nature of the
phenol).
A negative test (left)
and a positive test
(right)
Procedure
The unknown is added to dilute ethanol. A few drops of
dilute iron (III) chloride solution is then added.
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Assignment: Qualitative Analysis of Functional Groups
Test
Result
Iodoform Test
To determine the presence of ethanal and
methyl ketones
Reaction
The methyl group of the ketone (or second carbon of
ethanal) reacts with iodine and sodium hydroxide to form
iodoform (CHI3).
A negative test (left)
and a positive test
(right)
Procedure
Water, dilute sodium hydroxide, and iodine solution
(iodine and potassium iodide in water—a dark brownpurple colour) are added. A positive result is indicated by
the formation of a light yellow precipitate.
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Assignment: Qualitative Analysis of Functional Groups
Test
Result
Potassium Permanganate Test
To determine the presence of aldehydes, alkenes, and
phenols
Reactions
Aldehydes are oxidized to carboxylic acids, alkenes are
oxidized to diols , phenols react in various ways
(although the bonds of the benzene ring are not involved
in the reactions). All reactions create manganese (IV)
A negative test (left)
and a positive test
(right)
oxide, a brown precipitate.
Procedure
The unknown is dissolved in water and ethanol. The
potassium permanganate solution (purple) is then added
and mixed.
2. Create a data table with eight columns: one column for each test, as well as one
column for solubility in water and one for boiling point. It should include five rows,
one for each unknown. See the sample below for unknowns 1-5.
Unknown
Sol. in
water
Boiling
point
Cerric
Nitrate
Chromic
Acid
DNPH
Iron
Chloride
Iodofor
#1
#2
#3
#4
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Unknown
Assignment: Qualitative Analysis of Functional Groups
Sol. in
Boiling
Cerric
Chromic
water
point
Nitrate
Acid
Iron
DNPH
Chloride
Iodofor
#5
3. Contact your teacher to determine which five unknowns you’ll be testing. They
will be assigned to you at random. The unknowns are arranged into groups of
five to optimize page loading time.
a. Group One: unknowns 1-5
b. Group Two: unknowns 6-10
c. Group Three: unknowns 11-15
4. Select the appropriate links below to access the results of each unknown you’ve
been assigned. Read through the results of the eight tests for each of your five
unknowns. Each slide contains the results of the tests on one unknown.
 Remember, you are only responsible for analyzing the five unknowns assigned
to you.
Group One
 Group Two
 Group Three

5. Record your observations in your data table. (10 marks)
6. Complete the following questions
Questions
1. What is the identity of each of your unknowns (e.g. aldehyde, alcohol, etc.)?
Provide support for your choice. (10 marks)
2. Give a possible IUPAC name for each of your unknowns. (Hint: solubility and
boiling point can give you an idea of the length of carbon chain of an unknown.
As a general rule, monofunctional compounds with three or fewer carbons will
be soluble in water, whereas those with six or more will be insoluble.) (5 marks)
3. Using the tests in this experiment, would you be able to distinguish between
each of the following compounds if they were given to you as unknowns? Explain
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Assignment: Qualitative Analysis of Functional Groups
your answers.
a. 2-propanol and ethanol (2 marks)
b. 2-butanone and propanal (2 marks)
Assessment Details
Your submission should include the following:

Your completed observations chart

The answers to all questions, including rationale
Upload your submission to the Assignment: Qualitative Analysis of Functional
Groups Dropbox.
Submit this assignment to the dropbox. This assignment will be evaluated for a grade that will
contribute to your overall final grade in this course.
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