Lab8 Part II (Major Assessment) Determine an Unknown Organic Substance. the Report

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

http://en.wikipedia.org/wiki/Chemical_compounds

http://en.wikipedia.org/wiki/Molecules

http://en.wikipedia.org/wiki/Carbon

http://en.wikipedia.org/wiki/Carbonates

http://en.wikipedia.org/wiki/Cyanides


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.


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


20𝑚𝐿 𝟏𝟓.𝟕𝟕


20𝑚𝐿 𝟐𝟔.𝟒𝟎


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


20𝑚𝐿 𝟏𝟗.𝟖𝟔


20𝑚𝐿 𝟐𝟎.𝟗𝟖


20𝑚𝐿


THIS

BLANK

PAGE

IS

WHERE

THE

FLOWCHART

GOES


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


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.


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.



Tertiary alcohols 2-methyl-2-propanol

Ketones Propanone


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.


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.



Ketones Propanone


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.


Propanone has now been ruled out as ketones have been eliminated because the unknown organic substance has been found to be an alkyl halide.


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


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.

Documents

Lab8 Part II (Major Assessment) Determine an Unknown Organic Substance. the Report