Describe the complete combustion of alcohols.

Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water. This reaction is exothermic, releasing a large quantity of energy in the form of heat.


For example, the equation for the combustion of ethanol is C2H5OH + 3O2 ➔ 2CO2 + 3H2O.

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Describe the oxidation of alcohols by potassium dichromate(VI).

When heated in a solution of acidified potassium dichromate(VI), alcohols undergo oxidation to varying degrees depending on their structure. Primary alcohols are oxidised to aldehydes and carboxylic acids, while secondary alcohols are oxidised to ketones. Tertiary alcohols, however, do not undergo oxidation with potassium dichromate(VI).


For example, ethanol is oxidised to ethanal: C2H5OH + [O] ➔ C2H4O + H2O.

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Describe and explain the colour change that occurs during the oxidation of alcohols by acidified potassium dichromate?

The solution changes from orange to green.


This is because orange Cr2O72- ions are reduced to green Cr3+ ions.


The half-equation for this reaction is: Cr2O72- + 14H+ + 6e- ➔ 2Cr3+ + 7H2O.

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How do the conditions of the oxidation of primary alcohols influence the product formed?

If the alcohol is heated gently using a stoichiometric amount of oxidising agent, the aldehyde can be removed from reaction mixture using distillation.

If the alcohol is heated under reflux using an excess of oxidising agent, the carboxylic acid is formed. 

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What are the oxidation products of primary and secondary alcohols?

Primary alcohols can be oxidised to aldehydes or carboxylic acids.

Secondary alcohols are oxidised to ketones.


Tertiary alcohols do not undergo oxidation.

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Describe, and give the general word equation for, the dehydration of alcohols.

Alcohols are heated under refux in the presence of a catalyst to produce an alkene. The catalyst is can be concentrated sulfuric acid, concentrated phosphoric acid, or heated aluminium oxide powder.


Alcohol ➔ alkene + water


For example, ethanol undergoes an elimination reaction when dehydrated to form ethene: C2H5OH ➔ C2H4 + H2O.

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Name and describe the position of the functional group in aldehydes.

The functional group of aldehydes is the carbonyl (C=O) group which is located at the end of the hydrocarbon chain.

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Name and describe the position of the functional group in ketones.

The functional group of ketones is the carbonyl (C=O) group which is located within the body of the hydrocarbon chain.

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Explain how aldehydes and ketones can be distinguished using Fehling’s solution.

Aldehydes are oxidised to carboxylic acids when warmed with Fehling's solution, which results in a colour change from blue to brick red due to the formation of a copper(I) oxide precipitate.

Ketones do not react with Fehling's solution so the solution remains blue.

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Explain how aldehydes and ketones can be distinguished using Tollens' reagent.

Aldehydes are oxidised to carboxylic acid when warmed with Tollens' reagent, which results in the formation of a silver mirror on the inside of the test tube due to the reduction of silver ions (Ag+) to metallic silver (Ag).

Ketones do not react with Tollens' reagent so do not produce the silver mirror.

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