Chapter 15 - Alcohols

Question 1

What is main method use to produce alcohols industrially?

Answer 1

Alkenes are hydrated using an acid catalyst

Question 2

How else can ethanol be produced?

Answer 2

Via the fermentation process, where glucose is broken down by yeast in anaerobic conditions to release the by-product of ethanol, which can then be distilled

Question 3

What can ethanol produced this way be considered as?

Answer 3

A biofuel, because it is essentially only releasing carbon trapped by the source of glucose (usually sugarcane) absorbed from the atmosphere during its lifespan

Question 4

Why is ethanol produced by fermentation not a carbon neutral biofuel?

Answer 4

Becuase it has to be extracted using fractional distillation which requires fuels to be burnt, and then it is transported across the world which also uses fuel, usually from crude oil

Question 5

What mechanism is used to produce ethanol and what is the reaction conditions?

Answer 5

Ethene (usually obtained from cracking of alkanes) is reacted with steam is the presence of an acid catalyst to form ethanol via electrophilic addition

Question 6

What is the difference between primary, secondary and tertiary alcohols and how are they identified?

Answer 6

Primary alcohols and -COH groups which are only bonded to one other carbon (the end of carbon chains) whereas secondary -COH are bonded to 2 alkyl groups and so on for tertiary alcohols

Question 7

How are primary alcohols oxidised and under what conditions?

Answer 7

Primary alcohols are oxidised by acidifed potassium dichromate (K2Cr2O7) which starts orange, and after successfully oxidising turns green. If oxidised under reflux and then distilled, primary alcohols will form carboxylic acids, however if only distilled they will instead form aldehydes

Question 8

How are secondary alcohols oxidised

Answer 8

Secondary alcohols are oxidised by acidifed potassium dichromate to form ketones

Question 9

How are tertiary alcohols oxidised?

Answer 9

Tertiary alcohols are very rarely oxidised

Question 10

What are chemical tests to distinguish carboxylic acids and aldehydes?

Answer 10

Aldehydes will form a “silver mirror” in the presence of Tollens Reagent and also will turn Fehling’s solution red, whereas carboxylic acids will react with sodium hydrogencarbonate and effervesce

Question 11

What can be formed from alcohols

Answer 11

Alkenes can be formed by elimination with an acid catalyst, and can then be used in addition polymerisation, without the need for crude oils