Identification of an Unknown Organic Compound

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Identification of an Unknown Organic Compound

The aim of this coursework is to outline a sequence of simple chemical tests that can be used to identify the unknown organic compound. The unknown organic compound could contain any one of the following functional groups:

  • Alkene
  • Primary Alcohol
  • Tertiary Alcohol
  • Aldehyde
  • Ketone
  • Carboxylic Acid
  • Ester
  • Phenol

I will be listing all the tests in order and under each test, I will state the apparatus, chemicals needed for that test along with the method, the quantities of the chemicals, the observations for a positive result and any safety precautions regarding the test. The general safety and hazards are listed at the end which applies to all of the tests. I am also going to produce a flow chart which gives a clear outline of each test and what that tests determines. The flow chart summarising all these tests is included at the end.

Test 1 – Phosphorus Pentachloride:

This test gives a positive result if a hydroxyl group (OH) is present. It’s a Positive test for Alcohols, Phenols and Carboxylic Acid.

Apparatus and Chemicals list:

  • Test Tube
  • Test tube rack
  • 3cm3 Pipette
  • 10cm3 Measuring Cylinder
  • Spatula
  • Weighing boat
  • Weighing Scale
  • Solid Phosphorus Pentachloride
  • Acetone
  • Damp Blue Litmus paper

Method and Observations:

If the unknown compound is in a solid state then using the weighing boat and weighing scale, weigh approx. 0.50g of the compound and add it into a test tube. Then using the measuring cylinder, measure 5cm3 of acetone solvent, pour it into the test tube containing the unknown compound and stir the mixture so it’s completely dissolved. If the unknown compound is in liquid state then using a pipette, add 2.5cm3 of the compound into a test tube. Then place the test tube in a test tube rack in a fume cupboard and gently add a spatula of solid phosphorus pentachloride bit by bit, making sure that the product doesn’t come in contact with water, and hold the damp blue litmus paper above the test tube. If steamy white fumes are given off which turn the blue litmus paper red, then the test is positive for a hydroxyl (OH) group being present. If no reaction occurs, then the test is negative.

This means that the unknown compound could either be an Alcohol (Primary/Secondary or Tertiary), Phenol or a Carboxylic Acid.

If positive result obtained then do Test 2. If negative result obtained, then do test 7.

Safety and Hazards:

  • Phosphorus Pentachloride is harmful and very corrosive. It can cause burns if comes in contact with damp skin so make sure you don’t spill it when adding it. Always work in the fume cupboard because inhaling the fumes can damage the respiratory system. Seek immediate medical attention if any contact with the chemical is made.
  • 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 2 – Neutral Iron (III) Chloride:

This test gives a positive result for Phenol.

Apparatus and Chemicals list:

  • Test Tube
  • 3cm3 Pipette
  • Neutral Iron (III) Chloride solution
  • Spatula

Method and Observations:

Add a spatula or 2.0 cm3 of the unknown compound into a test tube. Then add 1.0cm3 of the aqueous Neutral Iron (III) chloride solution to the test tube containing the unknown compound and gently shake it. If there is a colour change to violet/purple then it’s a positive test for Phenol. If there’s no colour change then the test is negative.

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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 ...

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