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In this investigation I will get a number of unknown organic compounds to which I have to identify using a number of different chemical and physical techniques.

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Shama Lalji IDENTIFICATION OF AN ORGANIC UNKNOWN INTRODUCTION In this investigation I will get a number of unknown organic compounds to which I have to identify using a number of different chemical and physical techniques. The flow-chart below shows the chemical techniques I will use to identify the functional group of the unknowns. (1.TEST WITH UNIVERSAL INDICATOR) TURNS RED TURNS ANY OTHER COLOUR (2.TEST WITH BROMINE WATER) (3.TEST WITH 2,4 DNPH) (4.TEST WITH TOLLENS REAGENT) General safety procedures Always wear gloves and goggles when handling any unknown because some materials could be corrosive or an irritant. Be careful when disposing organic materials insure there is an organic waste beaker or bucket available. 1. Test unknown with Universal indicator 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. ...read more.


When the silver nitrate is mixed with ammonia to form Tollen's reagent, the complex ion [Ag (NH3) 2]+ is formed. This is reduced to silver during the process; Tollen's 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 hazcards 87, 91 and 6. EQUIPMENT: Test tube Pipette Silver nitrate solution Sodium hydroxide solution Ammonia solution Water Bath 5. Test to find an alcohol PROCEDURES: Add 1cm� of potassium dichromate into a test tube also add 1cm� of sulphuric acid to the test tube and add a few drops of the unknown and warm using a water bath. OUTCOMES: A colour change to green shows an alcohol is present. No colour change shows an ester. EXPLANATION: Primary alcohols are oxidised by acidified dichromate to aldehydes and then to acids. C2H5OH + [O] --> CH3CHO + H2O [O] is the oxygen from the oxidising agent then CH3CHO + [O] --> CH3COOH If this is done with a secondary alcohol, only a ketone forms. In each oxidation, the dichromate is reduced to Cr3+ (green). ...read more.


The chemical techniques I used only gave the functional groups of the unknowns and I cannot find out what exactly the unknown is by just using these techniques. I had to use the physical techniques as well. With all the chemical techniques there was always the possibility that an error could occur through the contamination of equipment, chemicals or the unknowns themselves. This would result in an incorrect result so therefore I paid particular care when taking part in this experiment. The mass spectrum gave me the relative atomic mass of the unknown this can be used to find a molecular formula however this 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 an unknown. The infrared spectrum doesn't simply make a distinction between an aldehyde and ketone so other tests would be required 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 with impurities so I would have to make sure the unknown was pure. 1 ...read more.

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