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Organic Qualitative and Quantitative Analysis

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Introduction

Experiment 4 Organic Qualitative and Quantitative Analysis Date performed: Nov 18, 2004 Oleksandr Halytskyy Lab sect. 21 TA: Andrew Chan Chm140y Purpose: The purpose of the experiment was to become familiar with tests for different organic compounds (i.e. an aldehyde, a ketone, a primary alcohol, a secondary alcohol and an ester) in order to identify the functional group of an unknown organic compound. Dumas method was then used to determine the molar mass of the unknown organic compound. Method: Five known compounds and one unknown were given. A test was performed on each of the five compounds using a specific reagent for every compound. The five known compounds were: i. an aldehyde ii. a ketone iii. a primary alcohol iv. a secondary alcohol v. an ester i. Testing for aldehyde involved adding one drop of aldehyde to one millilitre of Tollen's reagent in a test tube and allowing the mixture to react for less than 10 minutes before noting down the result. ii. Testing for the ketone required placing 2 drops of the ketone in a test tube with about 1 ml of the 2,4-dinitrophenylhydrazine reagent, which was then sealed and shaken to accelerate the reaction. ...read more.

Middle

v. The odour of the unknown was then noted and compared to the odour of the ester sample. The results of the tests of the unknown were then compared to each of the five tests performed on each of the five known substances. The results that showed the greatest similarity indicated the functional group of the unknown to be the same as on the known compound with the similar observations. To find the molar mass of the unknown compound Dumas method was used. The molar mass of a volatile liquid is equal to the molar mass of its vapour, assuming that the liquid neither dissociates nor associates in the progress. To find the molar mass of the vapour, a known volume was captured at known temperature and pressure. The vapour was then condensed and its mass measured. A 125 ml Erlenmeyer flask was used as a container to trap the vapour. 4 ml of the unknown compound were placed in the Erlenmeyer flask; the liquid was then placed in boiling water and boiled off. A piece of aluminium foil with a pinhole was placed over top the flask to allow the liquid to evaporate but to preserve the vapour once all the liquid had boiled away. ...read more.

Conclusion

/ (number of moles) M = (0.3856g) / (0.005 mol) M = 77.12 g/mol The relative uncertainty in the molar mass was found using the following formula: ?z / z = V [(?x/x)2 + (?y/y)2] The relative uncertainty came out to be: ?M / M = V [(0.001L / 0.152 L)2 + (0.5K / 369�K)2 + (0.0002g / 0.3856g)2] = 6.7 x 10-3 Only a four carbon secondary alcohol could produce a molar mass similar to that obtained. The closest molar mass is the one of the butan-2-ol which is 74 g/mol. Since butan-2-ol has no structural isomers the unknown compound must have had the same molecular formula. H OH H H | | | | H - C - C - C - C - H M = 74 g/mol | | | | H H H H Conclusions: The unknown compound was found to be a secondary alcohol with a formula C4H9OH, and name butan-2-ol. The functional group of the unknown was determined to be the hydroxide because it reacted with the alcohol reagent. The time of reaction proved it to be a secondary alcohol. The molar mass was found using Dumas method and found to be 77 g/mol. That molar mass corresponds to the closest molar mass of a secondary alcohol butan-2-ol, with a molar mass of 74 g/mol. ...read more.

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