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Investigate the chemical properties of alkanols and phenol.

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Introduction

Carmen Tse 7C 21 Experiment 20 Chemical Properties of Alkanols and Phenol 24-09-2003 Objective To investigate the chemical properties of alkanols and phenol. Introduction: Alkanols and phenol are all from hydroxyl compound containing the functional group OH. In this experiment, the chemical properties of hydroxy compounds are studied and compared, the reactions involving cleavage of O-H bond including solubility, pH, reaction with sodium hydroxide, reaction with sodium and reaction with alkanoic acid. The reactions involving cleavage of C-O bond including the reaction with phosphorus pentachloride (PCl5) and reaction with acidified potassium dichromate. Results: AI Testing solubility and pH Ethanol Phenol pH Neutral with pH7 Acidic with pH4 Solubility Soluble in water Soluble in water AII Reaction with NaOH Ethanol Phenol Temperature No change Increase AIII Reaction with sodium metal Ethanol Phenol Pop Sound Test +ve indicate there is H2 evolved +ve indicate there is H2 evolved pH Alkaline with pH11 Alkaline with pH9 AIV Reaction with Alkanoic acid Ethanol Phenol Smell Sweet No reaction and smell BI Reaction with Phosphorus Pentachloride and silver nitrate solution Ethanol Phenol White ppt Clear with no reaction BII Reaction with Acidified Potassium Dichromate Colour change Ethanol Orange to green Propan-2-ol Orange to green 2 methylpropan-2-ol No change Phenol Orange to Dark Brown Conclusion: Phenol is more acidic than ethanol. ...read more.

Middle

For the reaction with sodium metal, both phenol and ethanol react and give out hydrogen indicated by pop sound test. It is a typical acid-metal reaction: 2Na(s) + 2ROH(aq) --> 2RO-(aq) + Na+(aq) + H2(g) Phenol reacts in a faster rate than ethanol as seen in the rate of bubbles given out. It is also due to the acidic properties of phenol is stronger than ethanol. After all the sodium metal had reacted, add water and test for the pH. Both sodium ethanoxide and sodium phenoxide are alkaline, but ethanoxide shows a higher pH than phenoxide. It may because the excess ethanol and phenol in the test tube will neutralize the alkaline. As ethanol is neutral and phenol is acidic, ethanoxide shows a higher pH than phenoxide. The water should be added to the test tube only when the sodium metal had reacted and dissolved totally. It is because water reacts more vigorous with sodium than ethanol. 2Na(s) + 2H2O (l) --> 2NaOH (aq) + H2 (g) In the reaction with alkanoic acid, ethanol reacts with alkanoic acid to form a sweet smell compound. In fact it is a condensation reaction called esterification and the sweet smell compound is called ester. ...read more.

Conclusion

Primary alcohols are first oxidized to aldehydes and to carboxylic acid. In the experiment, ethanol is oxidized as follows: CH3CH2OH --> CH3CHOH --> CH3COOH Secondary alcohols can be oxidized to ketones and stop at ketones because further oxidation requires the breaking of strong C-C bond. In the experiment, propan-2-ol is oxidized as follows: For tertiary alcohols, like 2 methylpropan-2-ol in the experiment, are generally resistant to oxidation unless they are subjected to sever condition like strong oxidizing agent and heat. It is because any oxidation would immediately involve the cleavage of C-C bonds in alcohol molecules. In the experiment condition, only mild oxidizing agent Cr2O7- is used thus there is no reaction. For the phenol, it turned dark brown because phenol is oxidized to benzoquinone which is brown in color. Source of error and way of improvement: Phenol is a solid while ethanol is in aqueous solution. The amount of them is difficult to compare. For a fair test, phenol and ethanol should be in the same concentration and state. Phenol put in the air without cover will absorb water and dilute itself which will change the concentration of the reactants. Therefore phenol should be covered properly. ?? ?? ?? ?? 1 ...read more.

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