2.6 - Alcohols

Define miscibility

liquids that mix in all proportions

Define primary/secondary/tertiary alcohol

alcohol with one/two/three carbons directly bonded to carbon bonded to -OH group

General formula for alcohol with one hydroxyl group

CnH2n+1OH

How are alcohols named?

ending alkane name with no. to show position of OH group on C chain and add -ol or if 2 OH groups, -diol

What alcohols have structural isomers?

alcohols with 3 or more C atoms

Three types of alcohols

primary, secondary and tertiary

What are physical properties of smaller alcohols influenced by?

ability to form hydrogen bonds

Volatility of alcohols

H bonds are strong intermolecular forces and ability of alcohol molecules to form H bonds with themselves make them less volatile so bpt/mpt higher than expected

Solubility of alcohols

have both highly polar -OH group and non-polar hydrocarbon group. As series ascends -OH group becomes less important compared to increasingly large non-polar hydrocarbon chain so larger alcohols less soluble in water

Which alcohols are completely miscible in water?

smaller alcohols

How to prepare alcohol

reflux corresponding halogenoalkane with aqueous NaOH, liquid alcohol distilled off and purified by fractional distillation

What kind of reaction is preparation of an alcohol by refluxing corresponding halogenoalkane?

alkaline hydrolysis reaction taking place by nucleophilic substitution mechanism

What flame does ethanol burn with?

clean blue flame

When alcohols combusted in plentiful supply of air what is produced?

carbon dioxide, water and heat energy

What can ethanol be used as instead of others?

alternative fuel to petrol and other hydrocarbon fuels

Why is ethanol a cleaner fuel that octane in complete combustion?

less CO2, less soot causing photochemical smog and no sulfur impurities - combustion of causes acid rain

What kind of fuel is ethanol - environment?

carbon-neutral fuel as ethanol produced by fermentation of sugars made by photosynthesis. This uses CO2 balancing CO2 produced by ethanol combustion

What other fuel can ethanol be described as - source?

bio-fuel which is substance derived from biological material which burns to release energy

Method to react alcohol with sodium

put ethanol in test tube, add sodium, test gas produced with burning splint

Observations of reaction between alcohol and sodium

fizzing, solid sodium disappears and heat produced

Equation of reaction between ethanol and sodium

2C2H5OH + 2Na = 2C2H5ONa + H2

What are tests for an -OH

effervescence caused by production of H2 gas in addition of Na and misty fumes of HCl gas produced on addition of PCl5

What test is effervescence caused by production of H2 gas in addition of Na caused?

test for an -OH

How to react alcohol with hydrogen bromide

heat alcohol under reflux with HBr and corresponding halogenoalkane produced

Equation for reaction of ethanol with hydrogen bromide

C2H5OH + HBr = C2H5Br + H2O

Formal name for phosphorus pentachloride

phosphorus(V) chloride

Method for reaction between alcohol and phosphorus pentachloride

put ethanol in test tube, in fume cupboard add tip of spatula of phosphorus pentachloride, test gas produced with ammonia fumes

Observations of reaction between alcohol and phosphorus pentachloride

misty fumes, hissing, heat produced and PCl5 disappears

Equation of reaction between ethanol and phosphorus pentachloride

C2H5OH + PCl5 = C2H5Cl + POCl3 + HCl

What test are misty fumes of HCl gas produced on addition of PCl5?

test for -OH

Method for oxidation of alcohols

add dilute sulfuric acid and potassium dichromate(VI) soln to ethanol, warm in water bath and smell cautiously, repeat with propan-2-ol/2-methylpropan-2-ol instead of ethanol

Oxidation in primary ethanol changes - product created

oxidised, orange to green, ethanal

Oxidation in secondary propan-2-ol - product created

yes, orange to green, propanane

Oxidation in tertiary 2-methylpropan-2-ol

no, remains orange

How can primary, secondary and tertiary alcohols be distinguished from eachother?

reactions when warmed with oxidising agents like acidified potassium dichromate(VI) soln

What does primary alcohol form when warmed with oxidising agents such?

aldehyde, then carboxylic acid

What does secondary alcohol form when warmed with oxidising agents such?

ketane

What does tertiary alcohol form when warmed with oxidising agents such?

resistant to oxidation

If oxidation of an alcohol occurs, what colour change and smell will there be?

orange to green and change in smell

Oxidation of primary alcohols - full explanation

distillation and excess of the alcohol yields aldehyde, refluxing and excess of the potassium dichromate yields carboxylic acid