Mark Riley 3107631608 I dentification of an Unknown Organic 1
Identification of an Unknown Organic Compound
Mark Riley
Task Practical report
Introduction An organic compound is any member of a large class of chemical compounds whose molecules
contain carbon with exception of a few types of compounds such as carbonates, carbides and
cyanides. One or more of the carbon atoms are often covalently linked to atoms of other
elements, most commonly hydrogen, oxygen, or nitrogen. Organic compounds are found in
nature but can also be synthesized in the laboratory. We encounter so many organic compounds
everyday, such as when we use perfumes or even drink a glass of alcohol. Each organic
compound belongs to a particular chemical family and this experiment will investigate aldehydes,
ketones, alkyl halides, carboxylic acids and alcohols- culminating in an evaluation of to which
family an unknown organic sample belongs to.
Aim To identify an unknown organic compound using a pre-prepared flow chart.
Hypothesis By following the prepared flow chart, the unknown organic sample will be correctly identified.
(Provided that steps & procedures are followed as carefully and accurately as possible)
1. Follow the procedures in the series of tests outlined on the flow chart.
2. Using the results, determine the nature of the unknown organic compound.
3. Knowing the nature of the unknown compound, determine (even if by elimination) the family
to which the unknown sample belongs.
4. Use confirmation tests to confirm these results.
5. If there is more than one organic compound listed that belongs to this same family, conduct
further experimentation using boiling points or density to identify the compound.
(refer to flow chart and pages 5-9)
Method
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Equipment
Safety glasses
Lab coat
Rubber gloves
Test tubes
Blue litmus paper
Dropping pipettes
Bulb pipette
250mL beaker
Digital scales
Test tube rack
Bunsen burner
Heating mantle or oil bath
Reflux apparatus
Thermometer
Heat resistant mat
Tripod
Gauze
Retort stand
Clamp
Chemicals- o 1M H2SO4 (Sulphuric acid) o 0.1M K2Cr2O7 (Potassium dichromate) o 0.1M AgNO3 (Silver nitrate) o 2M NH3 (Ammonia) o NaHCO3 (Sodium bicarbonate) o 2-butanol o Sodium metal o 2-methyl-2-propanol o Ethanol o KOH (potassium hydroxide) o 2M HNO3 (Nitric acid)
Safety Precautions
Some of the chemicals being used are considered to be toxic and gloves as well as safety glasses should be worn throughout the experiment.
Check that the eye wash basin is functioning correctly before starting the experiment.
A pathway to the wash and eye wash basin should be clear at all times.
A chemical & flame retardant protective lab coat should be worn during the experiment.
Fully covered shoes must be worn.
Work benches should be kept clear and used equipment should be rinsed after use.
All chemicals being used should be clearly labeled.
Chemicals are flammable so open containers must be kept away from flames.
Much care should be taken when using sodium as it is very reactive.
Mark Riley 3107631608 I dentification of an Unknown Organic 3
Organic Compound
1-propanol 1-butanol 2-butanol 2-methyl-2-
propanol dichloromethane
Chemical Family
Alcohol Primary
Alcohol Primary
Alcohol Secondary Alcohol Tertiary Alkyl Halide
Chemical Formula
C3H8O C4H10 O C4H10 O C4H10O Cl2H2C
Structure
CONFIRMATION TESTS Use density wherever possible
Boiling point 97.4°C (96-98) 118°C (116-120) 99.5°C (99-101) 82.3°C (81-83) 61.7°C (96-98)
Density 𝟏𝟔.𝟎𝟕 𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 𝟏𝟔.𝟐𝟎
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 16.14
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 𝟏𝟓.𝟕𝟕
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 𝟐𝟔.𝟒𝟎
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿
Organic Compound methanal propanone propanoic Acid ethanoic Acid
Chemical Family Aldehyde Ketone Carboxylic Acid Carboxylic Acid
Chemical Formula CH3O C3H6O C3H6O2 C2H4O2
Structure
CONFIRMATION TESTS Use density wherever possible
Boiling point 100°C 56.1°C (55-58) 141°C (139-142) 117.9°C (116-119)
Density 𝟐𝟏.𝟓𝟔 𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 𝟏𝟓.𝟕𝟎
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 𝟏𝟗.𝟖𝟔
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿 𝟐𝟎.𝟗𝟖
𝐺𝑟𝑎𝑚𝑠
20𝑚𝐿
Mark Riley 3107631608 I dentification of an Unknown Organic 4
THIS
BLANK
PAGE
IS
WHERE
THE
FLOWCHART
GOES
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TEST 1.
Test Number 1
Equipment •Test tube •Test tube rack •Distilled water •Dropper •Blue litmus paper
Procedure (also see flow chart)
1. Add a few drops of distilled water into a test tube along with 10 drops of the unknown organic sample.
2. Test the mixture using blue litmus paper.
Observations The unknown sample and the water were miscible. The solution remained colourless and transparent. The
litmus paper did not undergo any colour change.
Discussion
Blue litmus paper will turn red if [H+] present which identifies a solution as acidic. From the organic compounds listed, only carboxylic acid will ionize to any extent (H-atom attached to the –OH group).
The litmus paper did not undergo any colour change and remained blue indicating the unknown solution was not acidic, thus eliminating carboxylic acid as a possible family to which the unknown sample could
belong to.
Families & compounds eliminated
The carboxylic acid family of organic compounds have been eliminated which include propanoic acid and ethanoic acid.
Remaining possibilities
Alkyl halides Dichloromethane
Primary alcohols 1-propanol, 1-butanol
Secondary alcohols 2-butanol
Tertiary alcohols 2-methyl-2-propanol
Aldehydes Methanal
Ketones Propanone
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TEST 2.
Test Number 2
Equipment •Test tube •Test tube rack •1M H2SO4 sulphuric acid •0.1M K2Cr2O7 potassium dichromate
•Dropper
Procedure 1. Place 10 drops of the unknown substance into a test tube. 2. Add 20 drops of 1M H2SO4 sulphuric acid into the test tube. 3. Add 5 drops of K2Cr2O7 potassium dichromate
Observations The solution was miscible and orange. The solution remained orange and no noticeable reaction occurred.
Discussion
K2Cr2O7 potassium dichromate is easily reduced & works as a mild oxidant. K2Cr2O7 is orange & when reduced (𝐶𝑟6+ → 𝐶𝑟3+) it turns green. When a reactant is reduced another reactant has been oxidized.
The only organic compounds listed that can be oxidised are as follows-
Primary Alcohol OXID→ Aldehyde Aldehyde OXID→ Carboxylic acid Secondary Alcohol OXID→ Ketone
A positive test (orange to green) therefore indicates that one of the substances underlined above is present. A carboxylic acid can be oxidized to CO2 + H2O but this is with much difficulty and for the purpose of this experiment will be ignored. In this test the solution remained orange, so there must not have been
any primary alcohols, secondary alcohols or aldehydes present. Therefore all three ofthese can be eliminated as possibly being the unknown organic sample.
Families & compounds eliminated
Primary alcohols have been eliminated which include 1-propanol and 1-butanol. 2-butanol is no longer a possibility either as all secondary alcohols have been eliminated. Methanol is from the aldehyde family
which has also been eliminated.
Remaining possibilities
Alkyl halides Dichloromethane
Tertiary alcohols 2-methyl-2-propanol
Ketones Propanone
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TEST 4.
Test Number 3
Equipment •Test tube •Test tube rack •Sodium metal •Dropper
Procedure 1. Add 5 drops of the unknown organic sample to a clean DRY test tube. 2. Carefully add a small piece of sodium metal to the test tube.
Observations There was no visible reaction. The sodium metal stayed in a solid state and underwent no transformation.
The unknown sample remained colourless and transparent.
Discussion
Just as sodium reacts with water to liberate hydrogen gas so too does sodium liberate hydrogen from alcohols or carboxylic acids. A positive test (fizzing as the hydrogen gas is released) indicates that the
substance is either a carboxylic acid or an alcohol. Because no reaction happened when the sodium metal was added to the unknown organic sample, it can now be deduced that the organic sample is not a tertiary
alcohol. This test has also further proved the results from the previous tests that had already eliminated primary alcohols, secondary alcohols and carboxylic acids as being the unknown organic sample.
Families & compounds eliminated
2-methyl-2-propanol is a tertiary alcohol and the possibility that the unknown organic sample may be a tertiary alcohol has now also been eliminated.
Remaining possibilities
Alkyl halides Dichloromethane
Ketones Propanone
Mark Riley 3107631608 I dentification of an Unknown Organic 8
TEST 5.
Test Number 4
Equipment •Test tube •Test tube rack •Dropper •0.1M AgNO3 silver nitrate solution •Ethanol •Potassium
hydroxide solid KOH •2M HNO3 Nitric acid •Blue litmus paper
Procedure (Alkyl halide test)
1. Add 6 drops of the unknown organic sample into a mixture of 12 drops of ethanol with a little solid KOH potassium hydroxide (the ethanol helped dissolve the KOH)
2. Cool mixture & add 2M HNO3 (nitric acid) until blue litmus paper turns red indicating solution is acidic.
3. Add 7 drops of AgNO3 (silver nitrate) solution.
Observations
The potassium hydroxide was added to the solution and reacted instantly. The solution heated up and bubbled as gas was released. After the potassium hydroxide had completely dissolved, the solution was
colourless and miscible. After the solution was made acidic and the AgNO3 silver nitrate solution was added, a white cloudy precipitate formed.
Discussion
This is an Alkyl Halide Test and a precipitate forming is a positive indication that the unknown organic
sample is a halo alkane and therefore the unknown organic sample must be dichloromethane. This test works because hallogens on carbon chains are easily displaced by hydroxide ions. An aqueous solution of
potassium hydroxide is a good source of hydroxide ions. In step 1, the unknown organic sample was added to a hydoroxide solution & the halogen was displaced. The solution is basic so drops of HNO3 Nitric Acid
were added to the solution until it just became acidic. The silver nitrate solution (nitrate because soluble in almost everything) was then added. (Acid+metal → salt+water). The white cloudy precipitate that formed
was AgCl.
Families & compounds eliminated
Propanone has now been ruled out as ketones have been eliminated because the unknown organic substance has been found to be an alkyl halide.
Mark Riley 3107631608 I dentification of an Unknown Organic 9
CONFIRMATION TEST
Confirmation Test
Equipment •Digital scales •Test tube •50 mL beaker •Bulb pipette
Procedure
1. Weigh and record the mass of the empty beaker 2. Using the bulb pipette measure 5 mL of the unknown sample 3. Add the 5 mL of the unknown sample to the beaker and record the new mass 4. Work out the mass of the 5mL sample of dichloromethane 5. Compare this mass with the expected mass per 1mL (density)
Results
Mass of empty beaker- 𝟐𝟗.𝟒𝟑 grams
Expected density of dichloroethane per mL- 𝟏.𝟑𝟐 grams
35.79g − 29.41g = 6.38g per 5mL
6.38g
5mL= 1.28 grams per mL
1.32 − 1.28 = 0.04
0.04
1.32× 100 = 𝟑% difference ( very small )
CONFIRMATION TEST IS POSITIVE FOR DICHLOROMETHANE
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CONCLUSION
The unknown sample was found to be dichloromethane from the functional group haloalkanes. The hypothesis was correct. By following the pre-prepared flow chart and the steps and procedures included in it carefully and as accurately as possible, the unknown organic sample was able to be identified. Flow charts can make identifying unknown chemicals and compounds a much simpler task.