4.29-4.33 Alcohols

What are alcohols?

Colourless liquids that dissolve in water to form neutral solutions

What are the first four alcohols commonly used as?

The first four alcohols are commonly used as fuels

What do all alcohols contain?

The hydroxyl (-OH) functional group

What is the formula of Methanol?

CH₃OH

What is the formula of Ethanol?

C₂H₅OH

What is the formula of propan-1-ol?

C₃H₇OH

What is the formula of butan-1-ol?

C₄H₉OH

What are the three different ways that ethanol can undergo oxidation?

1. Combustion (burning in air)

2. Aerobic oxidation

3. Treatment with an oxidising agent

What does the combustion of ethanol and oxygen produce?

Water and carbon dioxide

How (observation-wise) does ethanol burn readily?

Ethanol burns readily with an almost invisible blue flame

Why do school laboratories use ethanol in spirit burners?

In spirit burners, ethanol burns cleanly and without strong odours

What bacterium is responsible for the aerobic oxidation of ethanol in open wine?

Acetobacter (bacteria in the air)

What is the word equation for the aerobic oxidation of ethanol?

Ethanol + oxygen → ethanoic acid + water

Why does wine taste acidic or vinegary after being left open for several days?

Acetobacter bacteria use oxygen from the air to oxidise the ethanol in the wine into ethanoic acid (the carboxylic acid in vinegar)

What type of acid is ethanoic acid?

A weak carboxylic acid

What oxidising agent is used to oxidise ethanol in a laboratory setup?

Potassium dichromate(VI) in sulfuric acid

What is the chemical equation for the oxidation of ethanol using an oxidising agent?

CH₃CH₂OH + [O]  →  CH₃COOH + H₂O

What color change indicates that the oxidation of ethanol by potassium dichromate(VI) has occurred?

Solution changes from orange to green

Why is the reaction mixture heated when oxidising ethanol with potassium dichromate(VI)?

The reaction is slow, so heating it to its boiling point speeds up the process

Why is a condenser placed above the reaction flask during the oxidation of ethanol?

To prevent volatile liquids/substances from evaporating and escaping while heating (refluxing)

How is ethanol synthesised?

By the hydration of ethene

What is ethene a by-product of?

Ethene is a by-product of the cracking of hydrocarbons

What are the three conditions needed to hydrate ethene to make ethanol?

1. 300 degrees C temperature

2. 60-70 atm pressure

3. Concentrated phosphoric acid catalyst

Fill in the gap: Ethanol can also be produced by [ ] where sugar or starch is dissolved in water and yeast is added

Fermentation

What temperatures is the mixture fermented between and what is the optimum temperature [for a few days]?

The mixture is fermented between 25 and 35 degrees C, and the optimum temperature is 30 degrees C.

When yeast respires anaerobically, what does it form?

Ethanol and carbon dioxide

What kind of process is ethanol production and why?

Batch process: yeast are killed off once alcohol concentration reaches 15%

Yes/No. Is oxygen required for ethanol to be produced by fermentation?

No, fermentation is an anaerobic process