C15 - Alcohols

Question 1

Why are alcohols soluble in water?

Answer 1

Alcohols can mix with water because their molecules can form hydrogen bonds with water molecules

Question 1

Why can alcohols hydrogen bond?

Answer 1

The presence of the hydroxyl group with its electronegative oxygen atom means that alcohols are polar

Question 2

What factors effect alcohol soulbilty?

Answer 2

OH (hydroxyl) group increases solubility in water by hydrogen-bonding
Hydrocarbon chain length decreases solubility (due to apolar nature)

Question 3

What is a secondary alcohol?

Answer 3

Secondary (2°) alcohols have two R groups attached to the carbon to which the OH group is attached

Question 4

What happens when oxygen undergoes complete comustion?

Answer 4

It forms carbon dioxide and water

Question 5

What happens when primary alcohols are oxidised?

Answer 5

Primary alcohols can be oxidised to form aldehydes by an oxidizing agent [O] such as an aqueous solution of acidified potassium dichromate (VI) or potassium manganate(VII), KMnO4

Aldehydes contain a carbonyl group (C=O) at the end of the carbon chain, and are named using the suffix –al

If primary alcohols are reacted with an excess of oxidizing agent and refluxed, they can be oxidized to aldehydes and then further oxidised to carboxylic acids

Question 6

What happens when secondary alcohols are oxidised?

Answer 6

Secondary alcohols can be oxidized to ketones by an oxidizing agent. Ketones contain a carbonyl group (C=O) attached to any carbon in the chain except a terminal carbon atom, and are named using the suffix –one. Secondary alcohols must be heated under reflux gently with an excess of the oxidising agent to produce the ketone. Ketones cannot be further oxidised

Question 7

What happens when tertiary alcohols are oxidised?

Answer 7

Tertiary alcohols are resistant to oxidation due to the lack of hydrogen atoms on the carbon atom to which the hydroxyl group is attached

Question 8

What are the 2 ways of testing for aldehydes and ketones?

Answer 8

• Tollens’ reagentis an aqueous alkaline solution of silver nitrate in excess ammonia solution. Whenwarmedwith an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Ag+ions are reduced to Ag atoms, creating a silver mirror. Ketonescannot be oxidised and therefore give anegative testwhen warmed with Tollens’ reagent
• Fehling’s solutionis an alkalinesolution (OH-) containing copper(II) ions which act as the oxidising agent. Whenwarmedwith an aldehyde, the aldehyde is oxidised to a carboxylic acid and theCu2+ions are reduced to Cu+ions. Theclear bluecolour of the solution turnsopaquered due to the formation of a copper(I) oxideprecipitate. Ketonescannot be oxidised and therefore give anegative testwhen warmed with Fehling’s solution

Question 9

What happens in the oxidation of alcohols?

Answer 9

Alcohols can undergo dehydration to form alkenes with water as a by-product.. The water is from the -OH group and a H atom on the adjacent carbon atom.
A hot concentrated acid like sulfuric acid is used as the catalyst