Chapter 14 Flashcards
What important properties do alcohols have?
- They are polar and can form hydrogen bonds
List 3 differences between the properties of alkanes and alcohols.
- Alcohols have higher boiling points,
- are less volatile
- and are more soluble
Why do alcohols have higher boiling points than alkanes?
- They have hydrogen bonds
How does the boiling point of alcohols change as the chain length increases, and why?
- As alcohols get longer, their boiling points become more similar to those of alkanes
- This is because the contribution of the -OH decreases
Why are alcohols less volatile than alkanes of the same chain length?
- The higher the boiling point of a substance, the lower its volatility
Why are alcohols more soluble than alkanes?
- Hydrogen bonds form between the alcohol and water molecules, so alcohols are very soluble
- Alkanes are non-polar so they are insoluble
How can alcohols be classified?
- According to the number of other carbon atoms the carbon atom they are bonded to is bonded to
- In a primary (1°) alcohol, the carbon the hydroxyl group is attached to is bonded to one other carbon (e.g. ethanol)
- In a secondary (2°) alcohol, it is bonded to 2
- In a tertiary (3°) alcohol, it is bonded to 3
What happens when alcohols undergo combustion in a plentiful supply of oxygen?
- They produce carbon dioxide and water
How does the chain length of an alcohol affect its combustion?
- The longer the chain, the more energy released per mole
What oxidising agent is used to oxidate alcohols?
- Acidified potassium dichromate (VI)
- Written as: K2Cr2O7/ H2SO4
How can you tell if an alcohol is oxidised in the presence of potassium dichromate(VI), and why?
- The orange solution containing the dichromate ions goes from orange to green
- This is because the solution containing dichromate (VI) ions is reduced to a solution containing chromium (III) ions
What can primary alcohols be oxidised into, and what causes the difference?
- Aldehydes, when heated gently with acidified potassium dichromate and distilled as it’s formed
- Carboxylic acids, when heated under reflux with an excess of potassium dichromate
Why must alcohols be heated gently and distilled when forming aldehydes?
- To prevent further oxidation into a carboxylic acid
Why are alcohols heated strongly under reflux to make carboxylic acids?
- This ensures any aldehyde that is initially made is oxidised
Why are alcohols heated with excess potassium dichromate to form carboxylic acids?
- To ensure all of the alcohol is oxidised
