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An Experiment To Identify A Series Of Liquids

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Introduction

BACKGROUND THEORY ALKENES The alkene in this set of liquids is cyclohexene. It has the structural formula of CH2CHCHCH2CH2CH2. It has an intense, sharp smell. The test for alkenes is the addition of bromine water. In the event of an alkene being present, the bromine water, which is normally an orange-brown colour, will decolourise to leave a clear halogenoalkane. In this case, the halogenoalkane formed will be 1,2 - dibromocyclohexane. The reaction is electrophilic addition or in this case, halogenation. Equation: CH2CHCHCH2CH2CH2 + Br2 ==> CH2CHBrCHBrCH2CH2CH2 Cyclohexene bromine 1,2 - dibromocyclohexene HALOGENOALKANES Bromoethane is the halogenoalkane in the set of liquids given. It is also known as ethyl bromide, and has an ether-like smell. Its structural formula is CH2CH2Br. The test for halogenoalkanes is to add aqueous sodium hydroxide, then warm with ethanolic silver nitrate solution. If there is a halogenoalkane present, a precipitate of silver bromide will be formed. In the case of bromide ions, a cream precipitate will form; chloride ions form a white precipitate, and iodide ions form a yellow precipitate. ...read more.

Middle

Its structural formula is CH3COOH. The test for carboxylic acids is to add sodium bicarbonate solution. If a carboxylic acid is present, the solution will effervesce or fizz. The gas given off is carbon dioxide. Water is also formed, and the remaining compound is sodium acetate. The reaction is decomposition, and is reversible. Equation: CH3COOH + NaHCO3(alc) ==> CH3COONa + CO2 + H2O Ethanoic acid sodium bicarbonate sodium acetate carbon dioxide water WATER Water is the other chemical in this test. Its chemical formula is H2O. The test for water is to add anhydrous copper (II) sulphate solution. This solution is white, but after adding it to water, the solution will turn blue. The solution is now pentahydrate copper (II) sulphate, or chalcanthite. The reaction is hydration. Equation: 5H2O + CuSO4(l) ==> CuSO4.5H2O Water anhydrous copper (II) sulphate pentahydrate copper (II) sulphate METHOD * Place a few cm3 of each liquid into a separate test tube, labelling each with the appropriate letter label from the bottle. * Place the test tubes in the test tube holder * Add approximately 3cm3 of bromine solution, which will be orange-brown, to each test tube. ...read more.

Conclusion

o Rinse out the other test tubes and add the relevant chemicals to the three remaining tubes again. * Add approximately 3cm3 of anhydrous copper (II) sulphate to each test tube. o If the solution turns from white to blue, there is water present. The solution now contains pentahydrate copper (II) sulphate. o Rinse out the other test tubes and add the relevant chemicals to the two remaining tubes again. * Heat water in the kettle and pour into water bath if necessary * Add approximately 3cm3 of acidified potassium dichromate to each test tube, and warm in water bath. o If the solution turns from orange to green, there must be butan-1-ol, as this only occurs with primary or secondary alcohols; butan-1-ol is a primary alcohol. The other alcohol, methylpropan-2-ol is a tertiary alcohol, and so will not undergo a colour change. o Rinse out the remaining test tube and add the relevant chemical. * Add propanoic acid to the remaining test tube o The solution will remain colourless, but give off a sweet smell. This means that an ester is formed. This esterification is the confirmation of an alcohol, and means that methylpropan-2-ol must be present if the previous oxidation reaction did not occur. ...read more.

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