AQA A-Level Chemistry Alcohols

What is the general formula of alcohols?

CnH2n+1OH

What does the name end in?

-ol

What is the prefix of OH group?

hydroxy-

If there are 2 or more -OH groups then what is used?

di,tri..

What are the bond angles for all H-C-H bonds and C-C-O bonds?

109.5

What is the bond angle in H-O-C bond (bent-line shape) Explain.

104.5

2 bond pairs of electrons and 2 lone pairs

repelling to a position of minimum

repulsion. Lone pairs repel more than

bond pairs so the bond angle is

reduced.

Describe the volatility and boiling point in alcohols, due to their ability form what type of bond between alcohol molecules?

Relatively low volatility and

high boiling points due to their ability to form

hydrogen bond between alcohol molecules.

Describe the carbon cation formations?

Primary= 1 carbon attached to carbon adjoining oxygen

Secondary= 2 carbons attached to carbon adjoining oxygen

Tertiary= 3 carbons attached to carbon adjoining oxygen

What is the oxidising agent that causes alcohols to oxidise?

Potassium dichromate K2Cr2O7

Partial Oxidation of Primary Alcohols: what is the overall reaction between? Reagent used? Conditions?

Reaction: primary alcohol -> aldehyde

Reagent: potassium dichromate (VI) solution and dilute sulfuric acid

Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it forms:

What does the aldehyde's name end in? State the bonds?

-al C=O bond

on the first carbon of the

chain.

What symbol represents O from the oxidising agent?

[O]

In the oxidation equations what do you observe? CH3CH2CH2OH + [O] -> CH3CH2CHO + H2O

propan-1-ol propanal

Observation:the

orange dichromate ion

(Cr2O7 2-) reduces to

the green Cr 3+ ion

When writing the formulae of aldehydes in a condensed way, how do write C, H, O together?

CHO

In distillation, what is it generally used as?

Separation technique to separate

an organic product from its reacting mixture. In order to maximise yield collected, only collect the distillate at the approximate boiling point of the desired aldehyde and not higher.

Explain where and why the bulb of the thermometer should be placed?

At the T junction connecting to the

condenser to measure the correct boiling

point

Why is the water at the bottom of the condenser?

To go against gravity. This allows

more efficient cooling and prevents back flow

of water.

Why are electric heaters used to heat organic chemicals?

Organic chemicals are normally highly flammable and could set on fire with a naked flame.

What can be done to the collection flask to help improve the yield of distillate?

Cooled in ice

Full Oxidation of Primary Alcohols, what is the overall reaction between? Reagent? Conditions?

Reaction: primary alcohol -> carboxylic acid

Reagent: potassium dichromate(VI) solution and dilute sulfuric acid

Conditions: use an excess of dichromate, and heat under reflux: (distill off product after the reaction has finished)

In this equation what observation do you make?

CH3CH2CH2OH + 2[O] -> CH3CH2COOH +H2O

propan-1-ol propanoic acid

The orange dichromate

ion (Cr2O7 2-) reduces to the green Cr 3+ ion

When is Reflux used? What does the condenser prevent?

Used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping

by condensing them back to liquids.

Why should you never seal the end of the condenser?

As the build up of gas pressure could cause the apparatus to explode. This is true of any

apparatus where volatile liquids are heated including the distillation set up.

Why are anti-bumping granules added to the flask in both distillation and reflux?

To prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles.

Oxidation of Secondary Alcohols: What is the overall reaction? Reagent? Conditions?

Reaction: secondary alcohol -> ketone

Reagent: potassium dichromate(VI) solution and

dilute sulfuric acid.

Conditions: heat under reflux

What do ketones end in? When does it need a number to show the position of the double bond?

-one

5C's or more in a chain

What observation do you make in the equation propan-2-ol -> propanone

The orange dichromate ion (Cr2O7 2-) reduces

to the green Cr 3+ ion

Why can't tertiary alcohols be oxidised at all by potassium dichromate?

No hydrogen atom bonded to the carbon with the -OH group

Distinguishing between Aldehydes and Ketones:

Tollen's Reagent:

Reagent?

Conditions?Reaction:aldehydes only?

Observation: aldehydes, ketones?

Reagent: Tollen's reagent formed by aqueous ammonia + silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+ .

Conditions: heat gently

Reaction: aldehydes only are oxidised by

Tollen¡¦s reagent into a carboxylic acid. The

silver(I) ions are reduced to silver atoms

Observation: with aldehydes, a silver mirror

forms coating the inside of the test tube.

Ketones result in no visible change

CH3CHO + 2Ag+ + H2O „³ CH3COOH + 2Ag + 2H+

Distinguishing between Aldehydes and Ketones:

Fehling's solution:

Reagent?

Conditions? Reaction: aldehydes only?

Observation: aldehydes, ketones?

Reagent: Fehling's solution containing blue Cu2+

ions.

Conditions: heat gently

Reaction: aldehydes only are oxidised by Fehling's solution into a carboxylic acid. The

copper (II) ions are reduced to copper(I) oxide .

Observation: Aldehydes :Blue Cu 2+ ions in

solution change to a red precipitate of Cu2O.

Ketones do not react

CH3CHO + 2Cu2+ + 2H2O CH3COOH + Cu2O + 4H+

How can we test the presence of carboxylic acid?

Addition of sodium carbonate. It will fizz and produce carbon dioxide.

Reaction of Alcohols with Dehydrating Agents:

Overall reaction?

Conditions?

Role of reagent?

Type of reaction?

Reaction: Alcohol -> Alkene

Reagents: Concentrated sulfuric or phosphoric acids

Conditions: warm (under reflux)

Role of reagent: dehydrating agent/catalyst

Type of reaction: acid catalysed elimination

What is the definition of dehydration reaction?

Removal of a water molecule from a molecule

Forming Ethanol: Fermentation

Overall equation?

Conditions?

Optimum temp?

What happens at lower and higher temp than optimum?

Why is it done in absence of air?

Adv? Dis?

glucose -> ethanol + carbon dioxide

C6H12O6 -> 2 CH3CH2OH + 2 CO2

Conditions:

•Yeast

•No air

•temperatures 30 -40oC

Optimum temperature:38 oC

Lower temperatures: reaction is too slow.

Higher temperatures: the yeast dies and the enzymes denature.

Fermentation is done in an absence of air because presence of air causes extra reactions to occur. It oxidises the ethanol produced to ethanoic acid (vinegar).

Advantages

•sugar is a renewable resource

•production uses low level technology / cheap

equipment

Disadvantages

•batch process which is slow and gives high production costs

•ethanol made is not pure and needs purifying by fractional distillation

•depletes land used for growing food crop

Forming ethanol: from Ethene:

Reagent?

Equation and type of reaction?

Definition of hydration?

Essential conditions?

Adv? Dis?

Reagent: ETHENE - from cracking of

fractions from distilled crude oil

CH2=CH2 (g) + H2O (g) CH3CH2OH (l)

Type of reaction: Hydration/addition

Definition: Hydration is the addition of water

to a molecule

Essential Conditions

high temperature 300 °C

high pressure 70 atm

strong acidic catalyst of conc H3PO4

Advantages:

•faster reaction

•purer product

•continuous process (which means cheaper

manpower)

Disadvantages:

•high technology equipment needed (expensive

initial costs)

•ethene is non-renewable resource (will become

more expensive when raw materials run out)

•high energy costs for pumping to produce high

pressures

What is biofuel?

Fuel produced from plants

What does carbon neutral mean?

"an activity that

has no net annual carbon (greenhouse gas)

emissions to the atmosphere"

How is ethanol ( from fermentation is a biofuel) argued as carbon neutral?

Any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew. There would be no net CO2 emission into the atmosphere.