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Identification of an organic unknown.

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IDENTIFICATION OF AN ORGANIC UNKNOWN. PLANNING: Aim: To outline a sequence of simple chemical tests that I could use to identify each of the following groups: �an alcohol, �an aldehyde, �a ketone, �a carboxylic acid, �an ester and �a phenol. Introduction: I will be given one of the above organic unknowns and it is my job to investigate which one of them I have via methods of qualitative analysis. Firstly I will need to familiarise myself with each of the groups. Below is a diagram detailing how one group can be transformed into another. Such processes will need to be duly noted when planning the method for the identification of the unknown as we may unintentionally change the chemical structure of the unknown. I must now begin to investigate tests that identify particular groups. These I will have to string together and make into a flow diagram whereby each test is dependant on the result of the previous test. Name (and example) Functional Group Test for the presence of this specific group Alcohol (methanol) Heat and reflux with acidified potassium dichromate (K2Cr2O7 - orange). Unless alcohol is a tertiary alcohol, solution will form Cr3+ ions - blue - and there will be a colour change. Aldehyde (methanal - formerly 'formaldehyde') Aldehydes and ketones (carbonyls) will turn 2,4-dinitrophenylhydrazine (2,4-DNPH) orange in sulphuric acid and methanol. Adding an aldehyde to a clear solution which contains ions of [Ag(NH3)2]+ in a test tube in warm water will make a shiny silver mirror form. An alternative is to use copper (II) ions in an alkaline solution instead of the silver (I). The solution should turn from blue to red-brown. Ketone (propanone - formerly 'acetone') 2,4-DNPH undergoes a condensation reaction with aldehydes and ketones. Adding a ketone to the above mentioned chemicals ([Ag(NH3)2]+ and complexed Cu2+) would produce no results such as a shiny mirror surface or a colour change from blue to red-brown. ...read more.


and unless the alcohol is a tertiary alcohol, the solution will form Cr3+ ions - blue - and there will be a colour change. Now that I have explained and carefully thought out my flow diagram, I will begin to piece it together, beginning with the addition of sodium to the organic unknown. Method - step by step. Safety: As always, a standard risk assessment sheet will need to be filled out before any experiment can take place. Standard laboratory safety procedures should be observed for all off the methods following: �wear goggles �tie hair back �do not run �do not work on the edge of the work surface �turn Bunsen burner on yellow safety flame when not in immediate use �tuck stools under tables etc. Any safety procedures specific to the method will be mentioned after each method. What makes this experiment much more unsafe is the use of an unknown substance. Therefore extra care will need to be taken. Below is a table of the simplest organic compounds the unknowns can be with their risk and safety phrases. As all compounds in a homologous series behave similarly, I can deduce the risk and safety factors from one of those in the group and apply it to any one of them compounds. Organic unknown Risk phrases Safety phrases Alcohol (methyl alcohol) � Highly flammable � Toxic by inhalation � Toxic in contact with skin � Toxic if swallowed � Keep container tightly closed � Keep away from sources of ignition � Avoid contact with eyes and skin Aldehyde (formaldehyde, 37% solution) � Flammable � Very toxic by inhalation � Very toxic in contact with skin � Very toxic if swallowed � Causes burns � Possible risk of irreversible effects � Risk of serious damage to the eyes � May cause sensitisation by skin contact. � Wear safety glasses � Wear gloves � Keep room well ventilated. ...read more.


If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Flush skin with water" (http://physchem.ox.ac.uk/MSDS/DI/2,4-dinitrophenylhydrazine) Test 8: Tollens test Apparatus: �5cm3 Tollens reagent (ammonia solution added drop wise with shaking to silver nitrate) �2-4 drops of the organic unknown �pipette �test tube �water bath 1) prepare 5cm3 of Tollens reagent in a test tube 2) to this drop 2-3 drops of the organic unknown using the pipette 3) if there is no reaction, place test tube in a water bath in warm water 4) observe any physical changes in the appearance of the test tube Safety: Ensure the water in the water bath does not exceed temperatures over 30oC. The test tube must be washed thoroughly after use as if left to stand, can form explosive substances including the detonating material silver azide. A little concentrated nitric acid may be used to clean the test tube after use. Test 9: Add H2NOH to the unknown Apparatus: �5ml H2NOH in solution �5ml 'neutral' iron (III) chloride (10%) �5ml organic unknown �2 measuring cylinders (10ml) 1) add 5ml of H2NOH in solution into a test tube 2) to this, add 5ml of the organic unknown 3) in this mixture, add a few drops of 'neutral' iron (III) chloride 4) notice any colour changes Safety: Be sure to work away from the edge of the work surface. Wear goggles as iron (III) chloride can damage eyes. Test 10: smell the organic unknown Apparatus: �10 ml organic unknown �small conical flask 1) pour out 10ml of the organic unknown into a conical flask 2) whilst swirling the unknown, waft over vapours from the unknown towards your nose using your hands 3) notice any smells encountered Safety: Never directly smell unknown organics. Below is a table for which to record my results onto. I will place a tick for a successful test, a cross for an unsuccessful one and a dash of the test need not be completed. ...read more.

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