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Identification of an unknown organic compound

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Introduction

Identification of an unknown organic I have been supplied with an unknown organic compound containing one of the following functional groups: * Alkene * primary alcohol * tertiary alcohol * aldehyde * ketone * carboxylic acid * ester * phenol By completing a series of chemical tests, the functional group can be established and therefore what the organic compound is. Complete the following tests in this order in accordance with the flowchart and safety procedures, to identify the functional group. 1. Test to identify a C=C bond We will start with the bromine test. This particular test identifies phenols and the presence of unsaturated C=C bonds found in alkenes. Equipment required: * Bromine water * Unknown organic * Pipette * Test tube Procedure: Add the bromine water drop by drop to 1cm3 of the unknown compound a test tube and shake. Outcome for an alkene: The bromine water has a distinct orange/brown colour; an alkene will decolourise the bromine producing a clear liquid. Explanation: The C=C double bond in alkenes consists of a sigma bond and a ? bond, which increases its reactivity. The bromine atom becomes polarised when close to a region of negative charge such as the ? bond in the alkene, in this reaction it acts as an electrophile. ...read more.

Middle

If the test gives a negative result then continue onto test number 4. 3. Test to distinguish between an aldehyde and ketone After confirming the compound contains a carbonyl group, a positive result to the following test will confirm an aldehyde and a negative will confirm a ketone. Required equipment: * Silver nitrate solution * Dilute ammonia solution * Unknown compound * Water bath * Test tube * Pipette Procedure: Add dilute ammonia solution to 3cm3 of silver nitrate solution until the silver oxide precipitate dissolves. The solution now contains [Ag (NH3)2]+ ions. Add 10 drops of the unknown compound and warm the mixture in a water bath. Outcome for an aldehyde: An aldehyde will produce a silver mirror on the inside of the test tube. Explanation: Aldehydes are easily oxidised to acids. 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 and the aldehyde is oxidised to a salt of the corresponding carboxylic acid. The reaction is shown below: Outcome for a ketone: A ketone will not react, and no mirror will be produced. Explanation: A ketone has no available hydrogen atom on the carbonyl carbon that can be oxidized - unlike an aldehyde. ...read more.

Conclusion

Put a bung in the tube, shake vigorously and allow the mixture to stand. Outcome: The mixture will become cloudy or form an insoluble layer almost instantly due to the production of a chloroalkane. Explanation: The reaction is a substitution in which the chlorine replaces the hydroxyl group of the alcohol. If the test gives a positive result, the compound is a tertiary alcohol. If the test gives a negative result then the compound must be an ester Safety - Risk analysis Gloves, goggles and lab coats should be worn at all times throughout the experiment and long hair tied up. Take care if using Bunsen burner and any glassware. Be cautious with all chemicals used: * Do not inhale any vapours * Keep them * If they come into contact with skin wash the area thoroughly with water * Make sure not to rub face or eyes * Clean up any spillages immediately Follow the same safety precautions below for the unknown compound. Risk Cause Safety precautions Irritation to eyes and skin Bromine water 2, 4 DNPH Sulphuric acid Potassium dichromate Ammonia solution (Tollen's reagent) Lucas' reagent Avoid contact with skin and eyes. Wear eye protection and gloves; wash with cold water in the event of contact. Fire/explosion hazard Dry 2, 4 DNPH is extremely flammable and can be explosive. Ethanol is very flammable Tollen's reagent may explode on storage. Make sure the solid doesn't dry out. Avoid working near naked flames. ...read more.

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