Alcohols

What are Alcohols

it has the suffix “-ol” and has the general formula CnH2n+1OH

how to name alcohols

you need to know which carbon is attached to the functional group “OH” and how many functional groups are there.

Shape of Alcohols

the oxygen atom has two bonding pairs of electrons and two lone pairs. the COH angle is 105 because the lone pairs will repel the pairs of electrons in the covalent bond

Primary Alcohol

the carbon attached to the functional group is attached to 1 alkyl

Secondary Alcohol

the carbon attached to the functional group is attached to 2 other alkyls.

Tertiary Alcohols

the carbon attached to the functional group is attched to 3 other alkyls.

Hydrogen bonding in Alcohols

hydrogen bonding exists between the OH bond. the hydrogen bonds exist between the positive hydrogen atom and lone pairs of oxygen in other molecules.

Melting and boiling points of alcohols

hydrogen bonds are the strongest intermolecular force so a lot of energy is required to overcome this strong force so alcohols have a high melting and boiling point.

solubility of alcohols

as hydrocarbon chain in an alcohol increases, the solubility decreases. the hydrocarbon chains are forcing their way between water molecules and so they’re breaking hydrogen bond between those water molecules.

reactions of alcohols

combustion, dehydration, and oxidation.

Combustion

Alcohols burn completely to carbon dioxide and water or burn incompletely to carbon or carbonmonoxide.

Dehydration

Alkenes can be made by eliminating water from alcohols in a dehydration reaction which is the elimination of water.

Conditions of Dehydration of an Alcohol

concentrated sulfuric or phosphoric acid whihc is the dehydrating agent. the reaction needs to be under reflux.

General Formula of dehydration of an alcohol

CnH2n+1OH → CnH2n + H2O

First step of dehydration of an alcohol

a lone pair of electrons from the oxygen bonds to an H+ from the acid. the alcohol is protonated, giving the oxygen a positive charge

second step of dehydration of an alcohol

the positively charged oxygen pulls electrons away from the carbon

third step of dehydration of an alcohol

A water molecule leaves creating an unstable carbocation intermediate and the alkene is formed

What are the three ways to make ethanol?

Hydrating alkenes, fermentation of glucose, and nucleophillic substitution of a halogenoalkane.

Hydrating alkenes

Steam hydration of ethene is used industrially to produce ehtanol. Ethene can be hydrated by steam at 300c and 60atm. It needs solid phosphoric acid catalyst.

General equation of hydrating alkenes

C2H4 + H2O → C2H5OH

first step of hydrating an alkene

a pair of electrons from the double bond bonds to a H+ from the acid

second step of hydrating an alkene

a lone pair of electrons from a water molecule bonds to the carbocation and the water loses a H+ and the alcohol is formed

rate of reaction of hydrating an ethene

Very fast.

quality of product of hydrating an alkene

Pure alcohol is formed

Raw material of hydration of ethene

Ethene from oil which is a finite resource

Process/costs of hydration of ethene

continuous process so expensive equipment is required but low labour costs.

Fermentation of glucose

it is an exothermic process carried out by yeast in anaerobic conditions

Why is producing ethanol by fermentation important

As ethene comes from heavy cracking fractions of crude oil, crude oil will run out one day in the future so ethene will become more expensive so producing ethanol by fermentation will become more important in the future.

Conditions of fermentation of glucose

yeast produces enzymes which convert glucose into ethanol and carbon dioxide. the enzyme only works at optimum temperature of 30-40c.

Rate of reaction of fermentation of glucose

very slow

Quality of product of fermentation of glucose

very impure so it needs further processing

Raw material of fermentation of glucose

it uses sugars which is a renewable resource.

Process/costs of fermentation of glucose

its a batch process so cheap equipment is needed but high labour costs.

General equation of fermentation of glucose

C6H12O6 → 2C2H5OH + 2CO

What’s a biofuel

a fuel that’s made from biological material thats recently died

advantages of biofuel use

renewable energy reource so it won’t run out so they’re more sustainable. biofuels produce the same amount of carbon dioxide that the crop plant took in as it was growing so its carbon neutral.

disadvantages of biofuel use

land is used to grow crops for biofuel so that land can’t be used to grow food. trees may be cut down to create more land to grow crops for biofuels which destroys habitats and removes trees. fertilisers are added to soil to increase biofuel crop production which pollute waterways and release nitrous oxide.

What is used as the oxidising agent to oxidise alcohols

potassium dichromate

During the reaction what happens to potassium dichromate

it changes colour from orange to green

Primary alcohols can be oxidised to

Aldehydes and Carboxylic acids

Secondary Alcohols can be oxidised to

Ketones

How to produce just an aldehyde when oxidising a primary alcohol

by gently heating excess alcohol with a controlled amount of oxidising agent in a distillation apparatus. the aldehyde is distilled off immediately.

how to produce a carboxylic acid when oxidising a primary alcohol

the alcohol needs to be vigorously oxidised by mixing with excess oxidising agent and heating it under reflux

conditions and reagents of oxidisng a secondary alcohol

its heated under reflux, it uses acidified potassium dichromate

why can’t tertiary alcohols be oxidised

because the carbon bonded to the functional group doesn’t have enough hydrogens for it to be oxidised.

what are the two ways to test for aldehydes and ketones

reaction with tollens reagent and reaction with fehling’s solution

reaction with tollens reagent

the reagent is colourless. when it is added to an aldehyde it becomes a metallic silver. when it is added to a ketone, nothing changes.

reaction with fehling’s solution

the solution is blue. when an aldehyde is added to it, the solution becomes a brick red. when a ketone is added to it, nothing changes.