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Identification of an Organic Unknown.

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A-Level Chemistry Coursework Practical 1- Identification of an Organic Unknown Introduction In this investigation I will be supplied with a compound which will contain one of the following functional groups: * Alcohol * Aldehyde * Carboxylic acid * Ester * Ketone * Phenol The following is a flow diagram of the chemical tests I will use to identify the functional groups outlined above: (1.TEST WITH UNIVERSAL INDICATOR) TURNS RED TURNS ANY OTHER COLOUR (2.TEST WITH BROMINE WATER) (3.TEST WITH 2, 4 DNP) (4.TEST WITH TOLLENS REAGENT) General Safety Procedures For all experiments involving any unknown compound the wearing of goggles, lab coat and gloves is necessary because one or more of the compounds could be an irritant/corrosive/etc. 1. Test with Universal Indicator EQUIPMENT: Universal indicator Test tube Pipette PROCEDURE: Add several drops of the unknown substance to universal indicator inside a test tube using a pipette. OUTCOME: A colour change to red indicates either a carboxylic acid or phenol is present. Any other colour change shows alcohol, aldehyde, ketone or ester. EXPLANATION: Single indicators, such as litmus, are very weak acids. If the concentration of hydrogen ions is changed at a certain pH the indicator will change to a different structure. Universal indicator is a mixed indicator i.e. ...read more.


4. Test with Tollens Reagent EQUIPMENT: Test tube Pipette Silver nitrate solution Sodium hydroxide solution Ammonia solution Water Bath PROCEDURES: Put about 1cm� of 0.05M silver nitrate solution into a very clean test tube and add 3 or 4 drops of sodium hydroxide solution. Drop by drop; add ammonia solution until the precipitate of silver oxide nearly dissolves. Add a few drops of unknown to the tube and shake gently. Place tube in a beaker of warm water, note observations and immediately rinse out test tube. OUTCOMES: A change from clear to a silver mirror precipitate on the side of the test tube indicates the presence of an aldehyde. No change indicates a ketone. EXPLANATION: Aldehydes are easily oxidised to make them acids. Ketones cannot be oxidised, as there is no place for the oxygen from the oxidising agent. When the silver nitrate is mixed with ammonia to form Tollens reagent, the complex ion [Ag (NH3) 2] + is formed. This is reduced to silver during the process; Tollens reagent is the oxidising agent. SAFETY: Follow general safety procedures and silver nitrate solution, sodium hydroxide solution and ammonia solution are all corrosive so always make reference to the relevant hazcards. 5. Test with Acidified Potassium Dichromate EQUIPMENT: Test tube Pipette Potassium dichromate solution Sulphuric acid Water bath PROCEDURES: Add 1cm� of potassium dichromate ...read more.


To get a more specific answer I had to use the physical techniques as well. With all chemical techniques there is always a possibility of an error occurring through the contamination of equipment, chemicals or the unknown compound itself. This would result in an incorrect result so therefore I had to pay particular care when conducting all parts of the chemical tests. None of the spectra are particularly useful independently and only really come in to good use when one or more of them are used together. The mass spectrum gives the relative atomic mass of the unknown this can be used to give a general idea of the molecular formula. However the atomic mass could be appropriate to more than one functional group so I would not be able to use this technique on its own to find the identity of any organic unknown substance. The infrared spectrum doesn't simply make a distinction between an aldehyde and ketone so other tests would be required to make this distinction if this situation occurred. The NMR spectrum was very useful as it gave most information needed to identify an unknown. Another technique I could use to identify an unknown which I didn't use would be finding the melting and boiling points. There would however be difficulties if the compound contained any impurities so I would have to make sure the organic unknown was pure. ...read more.

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An excellent coursework that produces a very detailed series of tests for identification of organic compounds. This is an A Level coursework however it is classified under GCSE. This coursework might be extremely confusing for the GCSE level chemistry. The ...

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Response to the question

An excellent coursework that produces a very detailed series of tests for identification of organic compounds. This is an A Level coursework however it is classified under GCSE. This coursework might be extremely confusing for the GCSE level chemistry. The coursework is very clear and easy and well-organised to give the reader a very complete information about this procedure. The usage of diagram/chart to show the series of the reactions is incredible however for this level of coursework, diagrams for the apparatus used for each test should be included.

Level of analysis

The analysis of the experiment is good and produces a very detailed manual for the reader. However there can be some debate concerning some stages of the test. The usage of Universal indicator might not be accurate as the pH of phenol is above 5 and very close to 6 which is not easily detected by Universal indicator so usage of a digital pH meter or blue litmus paper would be a better option. I can also point out at the test used to distinguish between an alcohol and an ester. This test definitely works unless a tertiary alcohol is used as stated however we do not know if the alcohol is tertiary or not. so it is better to use Phosphorus pentachloride (PCl5) to detect alcohols as all alcohols produced steamy fumes of Hydrogen Chloride with PCl5. In another part of the coursework, If Brady's reagent test is negative it would only conclude that alcohol or ester is the compound since the posiblity of Phenol & Carboxylic acid is already eliminated before doing the test with the Brady's reagent. However in general this is a very excellent coursework.

Quality of writing

The grammar, spelling and the usage of technical terms are completely fine and there is nothing to be pointed out.

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Reviewed by alireza.parpaei 14/03/2012

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