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To identify an organic unknown using basic cohesive chemical tests to discover the functional groups present in the unidentified chemical.

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Introduction

Identification of an Organic Unknown Aim: To identify an organic unknown using basic cohesive chemical tests to discover the functional groups present in the unidentified chemical. There are six unknowns A-F including one of any of the following: Alcohol, Aldehyde, Ketone, carboxylic acid, ester or phenol. Each test used to identify the functional group must be dependant on the previous result. Therefore it is useful to use a flow chart to demonstrate the path of the test. Positive Negative Add a solution of 2,4 dinitropheylhydrazine Silver Mirror Test Add Sodium Hydrogen +ve Carbonate +ve -ve -ve +ve Add Sodium -ve Add Concentrated +ve HCl -ve But what makes these tests so conclusive. The first test is the reaction of 2,4 dinitrophenylhydrazine with the specific C=0 bond present in either an aldehyde or a ketone. The reaction creates a yellow precipitate and shows either a Aldehyde or a Ketone is present. A silver mirror test can then be carried out on the substance to find whether it is either a Aldehyde or a Ketone. Tollens reagent is added to the chemical in a test tube. The tube is placed in a beaker of boiling water and once heated if a silver coating forms on the outside of the test tube the compound is an Aldehyde if no coating is made the substance is a Ketone. ...read more.

Middle

This is achieved by research into the reagents to find which work best and which prove to be the most conclusive and what indications they give. Then when testing the compound it is important to notice precisely what the observations mean as the reliability of the whole experiment depends on good judgement. This judgement can be added by secondary test for example if you presume hydrogen is being released you can use a lighted splint to test to see if it is the case as if hydrogen is being liberated the splint should cause a small explosion or a pop. The risk factors involved are that many of the experiments use chemicals which can be classed as dangerous as they can be toxic or corrosive. Such chemicals require special care. For example when using a concentrated solution of HCl which is highly corrosive it is advisable to wear gloves and goggles to protect you from the acid. Other factors to take into account would be the use of equipment safely and accurately not only for the benefit of reliable results but also for your own protection. Conclusion: The outcome of my investigation proved that compound E was a carboxylic acid. This was discovered as E didn't react with 2,4 dinitrophenylhydrazine this meant that a ketone or aldehyde could be ruled out. ...read more.

Conclusion

In this case E was identified to be a carboxylic acid. But to further the identification and come up with a precise compound the spectra are required. Mass spectrum provides evidence of the compounds Relative Atomic Mass which in this case was 74. This on its own doesn't give much extra evidence to what the compound exactly was but combined with the other evidence it provides a check to prove the identification wrong or right. The I.R is slightly more useful at this stage. It shows us peaks at wave numbers of different functional groups identifying their presence. Although this should of all ready been deduced from the primary tests it acts as confirmation for the original conclusion. In compound Es case there is a peak for an OH group and C=O group which confirms that it is indeed a carboxylic acid. The most useful spectra as far as I am concerned is the nmr. This shows peaks for different protons telling us exactly what atoms make up the compound. The nmr tells us that the compound has in total 6 hydrogen atoms present with a triplet between 0.7-1.6 a R-CH3. A quartet between 2.0-2.9 for and a singlet at 11.7 for This suggests the following structure which also has a Mr of 74. The Mr of 74 confirms this structure so together with the three spectra and the primary chemical tests there has been a positive identification of E showing it to be propanic acid. ANDREW UNDERWOOD - 1 - 5/1/2007 ...read more.

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