Alcohols

Why are the boiling points of alcohols high?

They can form hydrogen bonds between alcohol molecules

Why can smaller alcohols dissolve in water?

They form hydrogen bonds with water molecules

What are primary alcohols?

Alcohols where 1 carbon atom is joined to the carbon joined to the oxygen

What are secondary alcohols?

Alcohols where 2 carbon atoms are joined to the carbon joined to the oxygen

What are tertiary alcohols?

Alcohols where 3 carbon atoms are joined to the carbon joined to the oxygen

What role does Potassium dichromate (K₂Cr₂O₇) play in the oxidation of alcohols?

Oxidising agent

When alcohols are partially oxidised what do they form?

Aldehydes

How do you identify an aldehyde from its displayed formula?

The C=O bond is on the first carbon in the chain

When writing the formula of aldehydes what do you do?

Write CHO and not COH at the end

Outline the reaction for the partial oxidation of alcohols to an aldehyde

What is the observation when alcohols are oxidised to aldehydes?

Orange to green

• Dichromate ion (Cr₂O₇^2-) is reduced to Cr³⁺ ion

What are the reagents for the partial oxidation of alcohols to aldehydes?

Potassium Dichromate (VI) solution and dilute sulfuric acid

What are the conditions for the partial oxidation of alcohols to aldehydes?

Warm gently and distil the aldehyde

Draw a labelled distillation apparatus

Why are electric heaters used in distillation and not naked flames?

As organic chemicals are normally flammable

What is formed in the full oxidation of alcohols?

Carboxylic acid

How do you identify a carboxylic acid?

It has a COOH group, with a C=O bond and an O-H bond

Outline the reaction for the oxidation of primary alcohols to carboxylic acids

What are the reagents for the full oxidation of alcohols to carboxylic acid?

Potassium dichromate (VI) solution and dilute sulfuric acid

What are the conditions for the full oxidation of alcohols to carboxylic acids?

Excess dichromate, so the alcohol is fully oxidised

Heat under reflux

What is the observation of the full oxidation of alcohols to carboxylic acids?

Orange to green

• Dichromate ion (Cr₂O₇^2-) is reduced to Cr³⁺ ion

Draw the labelled apparatus for reflux

Why should you never seal the end of a condenser during reflux?

Build up of gas pressure could cause an explosion

Why are anti-bumping granules added during reflux and distillation?

To prevent vigorous, uneven boiling by making small bubbles

What are the differences in oxidising alcohols to aldehydes and carboxylic acids?

Aldehydes : Limited dichromate and heat under distillation

Carboxylic Acids: Excess dichromate and heat under reflux

What is formed in the oxidation of secondary alcohols?

Ketones

How do you identify a ketone from its structural formula?

A C=O bond in the middle of the chain

Outline the reaction for the oxidation of secondary alcohols to ketones

What are the reagents used for the oxidation of secondary alcohols to ketones?

Potassium dichromate (VI) solution and dilute sulfuric aid

What are the conditions of the oxidation of secondary alcohols to ketones?

Heat under reflux

What is the observation for the oxidation of secondary alcohols to ketones?

Orange to green

• Dichromate ion (Cr₂O₇^2-) is reduced to Cr³⁺ ion

Why can tertiary alcohols not be oxidised?

There’s no hydrogen bonded to the carbon with the -OH group

How do you use Tollen’s Reagent to distinguish between Aldehydes and Ketones?

Tollens’ reagent oxidised aldehydes to carboxylic acids

• Silver mirror forms

Ketones have no visible change

How do you use Fehling’s Solution to distinguish between Aldehydes and Ketones?

Fehling’s solution oxidises aldehydes to carboxylic acids

• Blue Cu²⁺ ions change to a red precipitate of Cu₂O

Ketones have no visible change

How do you test for carboxylic acids?

Add sodium carbonate, which fizzes and produces CO₂

What are dehydrating reactions?

Removal of a water molecule from a molecule

When alcohols are dehydrated what do they form?

Alkenes

What type of reaction is alcohols to alkenes?

Acid-catalysed elimination reactions

What are the reagents for the dehydration of alcohols to alkenes?

Concentrated sulfuric or phosphoric acid

What is the role of the dehydrating agent?

Catalyst

Outline the mechanism from alcohols to alkenes

Why is producing alkenes from alcohols good for the environment?

Provides a route to creating polymers without using monomers derived from oil

What is the equation for fermentation?

Glucose —> Ethanol + Carbon dioxide

What are the conditions for the fermentation of glucose to form ethanol?

Yeast, No air, temperature 38 degrees

Why is a temperature of 38 degrees used, and not higher or lower

Optimum temperature for fermentation

• At lower temps the reaction is too slow

• At higher temps the enzymes denature

Why is there an absence of air?

Air can oxidise ethanol to ethanoic acid

Show the mechanism for the hydration of ethene to ethanol

What is a biofuel?

A fuel produced from plants

Why is ethanol produced from fermentation a biofuel?

As glucose is made in plants during photosynthesis

How is ethanol from fermentation a carbon-neutral process?

As any carbon dioxide given off is taken back in by plants during photosynthesis

What are the equations to show that fermentation of glucose is carbon-neutral?

• 6CO₂ + 6H₂O —> C₆H₁₂O₆ + 6O₂ (6 CO₂ molecules are removed from the atmosphere during photosynthesis)

• C₆H₁₂O₆ —> 2CH₃CH₂OH + 2CO₂ (2 CO₂ molecules released during fermentation of glucose)

• 2CH₃CH₂OH + 6O₂ —> 4CO₂ + 6H₂O (4 CO₂ molecules released during combustion of ethanol)

6 molecules absorbed and 6 emitted