Identification of an Unknown Organic Compound

The unknown compound is confirmed to be phenol.

If negative result obtained, then do test 3. The unknown could be an Alcohol (Primary/Secondary or Tertiary) or a Carboxylic Acid.

Safety and Hazards:

• Iron (III) chloride is corrosive and can cause burns. Make sure you don’t spill on to skin, so wear gloves when handling it. If a contact is made then rinse with water immediately and seek medical help if the problem further persists.
• Phenol is toxic and corrosive. Take care when handling it and make sure it doesn’t come in contact. Wear gloves when handling and eye goggles. Don’t inhale it as it’s harmful. If contact occurs, then wash with water immediately and seek medical help.

Test 3 – Ethanoic Acid Test:

This test gives a positive result for an Alcohol.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Water bath
• Spatula
• 400cm3 beaker
• Ethanoic Acid
• Sulphuric Acid

Method and Observations:

Add 2 spatulas or 2.5cm3 of the unknown compound into a test tube. Then add 2.5cm3 of Ethanoic acid into the same test tube alongside 10 drops of concentrated sulphuric acid. Then warm the mixture gently for 2-3 minutes in a water bath. Take the test tube out of the water bath and add it to the 400cm3 beaker containing 200cm3 of water. If a fruity sweet smell is given off then the test is positive for an Alcohol and the alcohol is oxidised to an ester. If no smell is distinguished then the test is negative.

If a positive result is obtained then, the unknown compound must be an Alcohol (Primary/Secondary or Tertiary), so do test 5. If the results were negative then the unknown compound must be a Carboxylic acid, so do test 4 to confirm it.

Safety and Hazards:

• Ethanoic Acid is harmful and corrosive. Make sure you wear gloves and eye goggles when handling it. Don’t let it come in contact with skin. If eye or skin contact is made then flush with plenty of water for at least 10 minutes and remove any contaminated clothing. Call for medical help.
• Concentrated Sulphuric Acid is harmful and corrosive. Always wear gloves and safety goggles while handling it. Make sure not skin contact is made. Keep it away from water. If eye or skin contact is made then flush with plenty of water for at least 10 minutes and remove any contaminated clothing. Call for medical help.

Test 4 – Sodium Bicarbonate:

This test gives a positive result for a Carboxylic Acid.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Spatula
• Methanol
• Saturated Solution of Sodium Bicarbonate
• Limewater

Method and Observations:

Add 1cm3 of methanol into a test tube. Then add 5 drops or a spatula of the unknown compound to the methanol. Then slowly add 1cm3 of the saturated sodium bicarbonate solution to that test tube. Carbon Dioxide gas is released. Add 5 drops of limewater to the solution and if the solution turns milky then the presence of carbon dioxide is confirmed. This then is a positive test for a Carboxylic acid. 

The unknown compound is confirmed to be a Carboxylic Acid.

Safety and Hazards:

• Methanol is toxic and highly flammable. Make sure it’s kept away from any source of ignition. Do not inhale or ingest as it can cause serious harm and could even be fatal. If it comes in contact with eye or skin then keep rinsing with water for some time. Remove any contaminated clothing as it can easily catch fire.
• Aqueous Sodium Bicarbonate is harmful. Contact with eyes and skin can cause irritation. If contact is made then rinse with plenty of water. Seek medical help if condition persists.
• Limewater is harmful and corrosive. Eye or skin contact can result in severe burns and irritation, so make sure that you wear safety goggles and gloves while handling it. Rinse with water if contact is made and call for medical help.

Test 5 – Acidified Potassium Dichromate:

This test gives a positive result for a Primary or Secondary Alcohol. It also gives a negative result for tertiary Alcohol and confirms it.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Spatula
• Acidified Potassium (VI) dichromate
• Water Bath
• Acetone
• Measuring cylinder

Method and Observations:

Add 1.0cm3 of the acidified potassium dichromate solution into a test tube. To the same test tube then, add 2.5cm3 of the unknown compound. If the unknown compound is in solid state then first add 2 spatulas of it in a separate test tube, measure 5cm3 of acetone and it to the unknown compound and stir it to dissolve it. Then add 2.5cm3 of this solution to the acidified potassium dichromate solution as mention earlier. Then gently warm the test tube containing the solution in a water bath for 5 minutes. If there is a colour change of the solution from orange to green, then it’s positive for a Primary or Secondary Alcohol. The alcohol is oxidised to an aldehyde and reduced green chromium (III) ions are produced. If there is no reaction and the colour of the solution remains orange, then it’s a negative test and confirms the compound to be a Tertiary Alcohol.

If the test was positive then do test 6. If the test was negative, then the compound is confirmed to be a Tertiary Alcohol.

Safety and Hazards:

• Acidified Potassium (VI) dichromate is toxic and corrosive. Take care when handling it and if eye or skin contact is made then rinse with water and seek medical help if needed. It is also a carcinogen.
• Acetone is only very slightly toxic and not much harmful. If an eye or skin contact is made then rinse with water immediately. If the problem continues then seek medical help.

Test 6– Tollen’s Reagent:

This is a positive test for an aldehyde. This test uses the solution obtained from test 5.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Tollen’s Reagent
• Water bath

Method and Observations:

In a test tube, add 2.5cm3 of the Tollen’s reagent. Then to the same test tube add 10 drops of the aldehyde solution obtained as a product from test 5. Warm the mixture in a water bath for 5 minutes. If there is a silver precipitate or mirror formed then the test is positive. If no reaction occurs and a precipitate isn’t obtained, then the test is negative.

If the test is positive, the unknown compound is confirmed to be a Primary Alcohol. If the test is negative, the unknown compound is confirmed to be a secondary Alcohol. But note that the unknown compound cannot be a secondary Alcohol in context of this experiment.

Safety and Hazards:

• Tollen’s reagent is corrosive. If there’s a skin contact, the area could become black in colour over couple days. Any contact should be immediately rinsed with water.

Test 7– Aqueous Bromine Water:

This is a positive test which confirms the presence of a C=C double bond and therefore an alkene or phenol.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Spatula
• Bromine Water

Method and Observations:

Add a spatula or 2.5cm3 of the unknown compound into a test tube. To the same test tube, add 2.5cm3 of brown bromine water. Shake the test tube gently. If the solution turns colourless without producing a precipitate then it’s a positive test. If no colour change occurs, then the test is negative.

If the test was positive, then the unknown compound is confirmed to be an Alkene.

If the test was negative, then the unknown compound could be an Aldehyde/ Ketone or Ester. Therefore do test 8.

Safety and Hazards:

• Bromine water is harmful. If prolonged skin contact is made, burns could occur. If there is a contact, then immediately rinse the area with water and ask for medical help if the condition persists.

Test 8– Brady’s Reagent:

This test is positive for an aldehyde or a ketone.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Spatula
• Methanol
• Aqueous Brady’s Reagent (2,4-dinitrophenylhydrazine)

Method and Observations:

Add 2.5 cm3 of Brady’s reagent in a test tube. Then add 10 drops of the unknown compound. If the unknown compound is in a solid state, then in a separate test tube add 2.5cm3 of methanol and 1 spatula of the unknown compound and dissolve the mixture. Then add 10 drops of this mixture to the test tube containing 2.5cm3 of Brady’s reagent as mentioned earlier. If there is a yellow/orange precipitate formed then the test gives a positive result. If no precipitate forms then the test is negative.

If a positive result is obtained then, the unknown compound could be an aldehyde or a ketone.

If a negative result is obtained then, the unknown compound is confirmed to be an ester.

Safety and Hazards:

• 2,4-dinitrophenylhydrazine is harmful, explosive and highly flammable. Do not let the product dry out as it will become explosive. Keep well away from source of ignition. Make sure you clean any spillages as they can dry out and could be potentially explosive. Any contact made should be rinsed with water.
• Methanol is toxic and highly flammable. Make sure it’s kept away from any source of ignition. Do not inhale or ingest as it can cause serious harm and could even be fatal. If it comes in contact with eye or skin then keep rinsing with water for some time. Remove any contaminated clothing as it can easily catch fire.

Test 9– Tollen’s Reagent:

This test gives a positive result for an aldehyde.

Apparatus and Chemicals list:

• Test Tube
• 3cm3 Pipette
• Spatula
• Methanol
• Aqueous Tollen’s Reagent
• Water Bath

Method and Observations:

Add 2.5cm3 of the Tollen’s reagent into a test tube. Then add 10 drops of the unknown compound to this test tube. If the unknown compound is in a solid state, then in a separate test tube add 2.5cm3 of methanol and add a spatula of the unknown compound to the methanol and stir it so it dissolves. Then add 10 drops of this solution to the test tube containing the 2.5cm3 of the Tollen’s reagent as mentioned earlier. Warm this test tube in a water bath for 5 minutes. If there’s a silver precipitate/mirror produced then the test is positive. If no precipitate forms then the test is negative.

If a positive result is obtained, then the unknown compound is confirmed to be an Aldehyde.

If a negative result is obtained, then the unknown compound is confirmed to be a Ketone.

Safety and Hazards:

• Tollen’s reagent is corrosive. If there’s a skin contact, the area could become black in colour over couple days. Any contact should be immediately rinsed with water.
• Methanol is toxic and highly flammable. Make sure it’s kept away from any source of ignition. Do not inhale or ingest as it can cause serious harm and could even be fatal. If it comes in contact with eye or skin then keep rinsing with water for some time. Remove any contaminated clothing as it can easily catch fire.

General Safety Precautions:

• Eye goggle must be worn at all times to avoid any eye contact with harmful chemicals.
• Lab Coats must be worn at all times to prevent any contamination of cloths.
• Chairs and Bags must always be kept under the tables to prevent any accidents and to consider the safety of others
• Always clean up any spillages and keep your work place tidy to reduce any accidents.

Bibliography:

• (http://www.chemguide.co.uk) – I used this website to retrieve value able information on different reactions in organic chemistry and their methods such as oxidation of alcohols, tests using Tollen’s reagent etc. This website is a very accurate and reliable source as it is a major chemistry website used all over the world and the contents of it are genuine if you compare them to those learnt in lectures and books.
• (http://ptcl.chem.ox.ac.uk) – I used this website to get all the information regarding the hazards involved with the chemicals used in this plan. A very accurate and reliable source as it is from a major education institution.
• (http://en.wikipedia.org.uk) – I used this site to get information on some chemicals such as acetone. The information provided contains a lot of depth and is accurate. Very reliable source as it is one of the biggest encyclopaedia online.
• (http://www.wellesley.edu) – I used this site to obtain information regarding the chemical test to distinguish a carboxylic acid. Reliable source as it’s an education institution.
• (http://www.chem.tamu.edu) – This site was used to get hazard information on saturated sodium bicarbonate. Reliable source as again it’s from an education institution.
• (http://www.jtbaker.com) – Used this site to get hazard information regarding limewater. Reliable source as they are a big industrial company providing different chemicals.
• (“Chemistry 2” by B.Ratcliff, H.Eccles) – I used this book to get more information on certain reactions of organic compounds such as the reactions of carboxylic acids and phenols. Very accurate and reliable as it’s a published book for A2 OCR students.
• (“Letts Revise A2 Chemistry” by R.Ritchie) – I used this book to learn more about the esterfication process. Very accurate and reliable source as it’s a published book and revision guide for students.

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