• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Identify an unknown organic compound.

Extracts from this document...


IDENTIFICATION OF AN ORGANIC UNKNOWN Introduction: In this assessed practical we have to plan a sequence of simple chemical test tube tests in order to identify an unknown organic compound containing a functional group. The functional group could be an alkene, primary alcohol, tertiary alcohol, aldehyde, ketone, carboxylic acid, ester or phenol. Safety: During all experiments Laboratory coats and safety glasses must be worn. When using a Bunsen burner tie long hair back and use a safety mat to protect the bench. Plastic gloves must be worn when handling the chemicals. There are some chemicals that need special attention when handling them: * 2, 4-DNP - is an irritant to skin and eyes. * Bromine water - is harmful if ingested or inhaled and prolonged skin contact can cause burns. It is an irritant to the eye and also make sure there is good ventilation. * Silver nitrate - is an irritant and can cause burns. * Ammonia - is an irritant and can cause burns. * Sodium hydroxide - is an irritant to skin and eyes. * Iron (III) Chloride - is toxic and can cause burns. Can also give off Hydrogen Chloride gas. * Sodium carbonate - is a low hazard, but still needs to be considered * Organic unknown - can be considered to be toxic and harmful if swallowed. If any of the above chemicals come into contact with skin or eyes, wash off immediately with cold water. ...read more.


A positive test will give a violet colour. Test 3 - 2,4-DNP Using a dropping pipette, place 5 drops of the organic unknown in a test tube. Measure out and add 2cm3 of 2,4-DNP solution. This is if the unknown is a liquid. If the unknown is a solid then measure out 20cm3 of de-ionised water and add 1g of the unknown solid and 2cm3 of 2,4-DNP in a test tube. Now do the same for the unknown if it is a liquid. Give the test tube a mix. A positive test will give an orange/yellow precipitate and a negative test will not give a precipitate. Test 4 - Tollens reagent (Ammoniacal Silver Nitrate solution) Take a 500cm3 beaker and fill it approximately half full with water. Place this on a tripod and gauze and heat the beaker of water using a Bunsen burner. Measure out 1cm3 of 0.05 mol dm-3 of silver nitrate in a measuring cylinder and place it in a test tube. Now add 5 drops of sodium hydroxide solution (2M) using a dropping pipette. Using a different dropping pipette, add 2M of ammonia solution drop wise until the precipitate has just dissolved. Then add 5 drops of the organic unknown and shake gently. Place the test tube in the beaker of warm water. A positive test will give a silver mirror on the inside of the test tube and a negative test will not give a mirror. ...read more.


Place this on a tripod and gauze and heat the beaker of water using a Bunsen burner. After the water has boiled, remove the flame and place the test tube into the beaker. Leave the test tube for about 5 - 10 minutes. A positive test will give a green coloured solution and a negative test will not give a green colour. Potassium Dichromate is a reagent, which oxidises alcohols when mixed with dilute sulphuric acid and warmed. The dichromate ion gives a colour change from orange to green, because it is reduced from an oxidation state of +6 to +3. However, this test does not oxidise a tertiary alcohol, therefore does not turn green. Alternative tests: For some of the tests that have been selected, there are alternatives that can be used. Firstly, to distinguish an aldehyde and a ketone, a test involving a solution called Fehling's can be used. This would involve mixing Fehling's A (aqueous copper sulphate), with Fehling's B (aqueous sodium hydroxide) and then adding the carbonyl. This test would give a brick red precipitate with an aldehyde but no precipitate with a ketone. However, Tollens will be used because it a test which is more familiar to me. An alternative test for an alkene that could be used is to add iodine in methylene chloride solution. This will produce a light tan solid, while retaining the purple colour of the iodine solution. However, this will not be used as it also gives a positive test for some alcohols and ketones. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Aqueous Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Aqueous Chemistry essays

  1. Peer reviewed

    Identification of an Organic Unknown.

    4 star(s)

    of ethanol, add several drops of the test substance using a pipette and heat with a water bath. OUTCOMES: A colour change to orange/yellow indicates the presence of a carbonyl group, which will be an aldehyde or a ketone. No colour change indicates that it is an alcohol, carboxylic acid, ester or phenol.

  2. To identify an organic unknown using basic cohesive chemical tests to discover the functional ...

    The tests are possible due to the different ways in which the functional groups react. This means to discover what compound you have you need to know simply how each functional reacts and what reagents can take advantage of this.

  1. ‘The Relative Strength of an Unknown Acid’.

    This second decimal place of a burette reading is only approximate and therefore is an error. An error of one drop in a volume of 25.20cm3 represents an error of 2%, but this has to be doubled because two burette readings are taken for each titration.

  2. Identification of an unknown organic compound

    Primary alcohols are oxidized on heating with acidified aqueous potassium dichromate: however tertiary alcohols remain unchanged with the reagent. (Chemistry 1 endorsed by OCR page 131 first paragraph). The test I will be using to identify whether it is a primary or tertiary alcohol will be by adding acidified potassium dichromate to the unknown organic compound.

  1. Identification of an Organic Unknown.

    Aldehydes carry a hydrogen atom next to their carbonyl group. This hydrogen is activated by the carbonyl group and is readily oxidised to OH. Aldehydes are therefore readily oxidised to carboxylic acids. Fehlings reagent is used to detect the presence of an aldehyde.

  2. identifying an unknown compound

    When the silver nitrate with ammonia to form Tollen's reagent then the complex ion is formed [Ag (NH3) 2) +.This is reduced to silver during the process. Tollen, s reagent is the oxidising agent. Equipment and reagent: * Test tube * Pipette * Silver nitrate solution * Sodium hydroxide solution * Ammonia solution * Water bath 5.

  1. Organic compound identification.

    Secondary Alcohol The infra red and the mass spectrum data both have told us that the unknown compound is a secondary alcohol; further chemical tests will reveal the real identity. Chemical Tests 1. Mix 1 - 2 cm3 of A with about 5 cm3 of tap water.

  2. Identification of an organic unknown

    * Hydrochloric Acid (HCl) * Ethanol * Lucas reagent [ZnCl2 - conc. HCl] Tabulated chemical tests Test Method Observation PCl5 Test For Hydroxyl groups, OH in Alcohols, Phenols and Carboxylic acid Pour 1 cm3 of sample into test tube in fume cupboard (making sure that the test tube is in a rack).

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work