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Identification of an unkown compound

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Introduction

Identification of an Organic Unknown (Skill P) Equipment: Test tubes Pipette Water Bath Sodium Bicarbonate Methanol Bromine Water 2, 4 DNPH Ethanol Silver Nitrate solution Sodium Hydroxide solution Ammonia solution Potassium Dichromate solution Sulphuric acid General safety: * In the event of getting a substance in my eye I will wash it out with cold water immediately. Safety goggles will be worn for all of the experiments. * If irritation is felt on my skin due to having contact with a substance I will wash the area of skin immediately with cold water. * If a spillage of any of the substances used occurs, I will notify those around me straight away. If the substance is not considered harmful I will clear it up personally, if it is hazardous I will inform a technician. * In the event of swallowing a harmful substance, medical help would be received be urgently requested. * Highly flammable substances must be kept at least 1 metre away form an open flame. * When tidying up at the end of my experiments it will be important to check those solutions that are safe to pour down the sinks and those that need to be handled with more care. 1) Test for an Alkene or Phenol The reaction of an alkene with Bromine water is an electrophilic addition reaction; the alkene will open up its double bond and form bonds between its carbon atoms and the electrophilic Bromine atoms. ...read more.

Middle

Once this is achieved add 2cm3 of 2,4 DNPH, using a pipette, to the solution and agitate for 1 minute, before leaving to stand for 5 minutes in a water bath . Result: The formation of a bright orange precipitate indicates the presence of a carbonyl compound, which will be an Aldehyde or a Ketone. If no change occurs then an unknown functional group still remains. Hazards: 2, 4 DNPH is explosive and toxic, so must be handled in a fume cupboard whilst wearing gloves. Also I am aware that ethanol is highly flammable, so it will be kept away from any open flames. 4) Test for an Aldehyde Aldehydes are easily oxidised to acids, whereas Ketones cannot be oxidised, as there is no place for the oxygen from the oxidising agent to attach on to. When the silver nitrate is mixed with ammonia to form Tollen's reagent, the complex ion [Ag (NH3) 2]+ is formed. [Ag (NH3) 2]+ + e- Ag (s) + 3NH2 This is reduced to silver during the process of oxidation. Tollen's reagent is the oxidising agent. Into a test tube, place 2cm3 of Silver nitrate solution and add 1 drop of dilute Sodium Hydroxide (NaOH). Add ammonia solution drop wise until the initially formed brown precipitate of silver oxide is re-dissolved. Then add 5 drops of Methanol to the solution and 5 drops of the unknown compound. ...read more.

Conclusion

Likewise, goggle must be worn as getting the reagent in your eye can be dangerous. 7) Test for a Carboxylic acid Using a Pipette add approximately 6 drops of the unknown compound solution and mix with 3 drops of methanol, to this then add 2 crystals of NaHCO3 and shake the test tube vigorously. Result: Solubility will be indicated by a colour change, or the evolution of Carbon dioxide. In this case a Carboxylic acid is present. To test for the evolution of Carbon dioxide, and thus the presence of a Carboxylic acid, the limewater test can be used. Lime water is a solution of calcium hydroxide (slaked lime). If Carbon dioxide is bubbled through it, a solid precipitate of Calcium Carbonate is formed. Calcium Carbonate is chalk or limestone, it is this that makes the lime water cloudy. calcium hydroxide + carbon dioxide calcium carbonate + water. Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l) Equipment: Bunsen burner Bung Rubber tube Hazards: Sodium Hydrogen Carbonate may cause skin irritation if constantly exposed to it, so gloves should be used. It is also Moisture sensitive so should be kept in a closed container, before and during the experiment. As mentioned earlier I am aware as to the dangers of Methanol. If all the tests prove a negative result then the unknown organic compound should be an Ester. All experiments should be carried out at least 3 times to be completely certain however. ...read more.

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