Chapter 14 - Alcohols Flashcards
What is the functional group of the alcohols?
-OH
What intermolecular forces do the alcohols have?
They have a polar O-H bond due to the difference in electronegativity between O and H, and therefore alcohols are polar. The intermolecular forces will be very weak London forces, but also much stronger hydrogen bonds between the polar O-H groups.
What is the difference in volatility of the alcohols and alkanes?
Alkanes - only weak London forces
Alcohols - strong hydrogen bonds hold alcohol molecules together (have to be broken to boil)
Therefore alcohols have a lower volatility to their relative alkane
What is the difference in water solubility between the alcohols and alkanes?
Alkanes are not soluble in water as they are non polar so cannot form H bonds with water
Alcohols are polar and the short chain ones like methanol and ethanol are completely soluble
What happens to the solubility of the alcohols in water as chain length increases?
As the hydrocarbon chain increases in size, the influemce of the -OH group becomes relatively smaller, and the solubility begins to decrease
What is a primary alcohol?
An alcohol where the OH group is attached to a C atom that is attached to 2 hydrogen atoms and one alkyl group.
What is a secondary alcohol?
An alcohol where the OH group is attached to a C atom that is attached to 1 hydrogen atom and two alkyl groups
What is a tertiary alcohol?
An alcohol where the OH group is attached to a C atom that is attached to no hydrogen atoms and three alkyl group.
How do alcohols combust?
Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water. The reaction is exothermic, releasing a large quantity of energy in the form of heat. As the number of C atoms in the alcohol chain increases, the quantity of heat released per mole also increases
What is used to oxidise primary and secondary alcohols?
A solution of potassium dichromate (VI) K2Cr2O7, acidified with dilute sulfuric acid, H2SO4
What happens to the acidified dichromate solution if the alcohol is oxidised?
The orange solution containing dichromate (VI) ions is reduced to a green solution containing chromium (III) ions.
Cr2O7 2- → Cr 3+
What are primary alcohols oxidised to?
Either aldehydes or carboxylic acids
How are aldehydes prepared from primary alcohols?
Primary alcohols gently heated with acidified potassium dichromate forming an aldehyde, which is distilled out of the reaction mixture as it forms - preventing further reaction with the oxidising agent.
How are carboxylic acids prepared from primary alcohols?
Primary alcohol heated strongly under reflux, with an excess of potassium dichromate, to ensure that all of the alcohol is oxidised. Heating under reflux insures any aldehyde formed also undergoes oxidation to the carboxylic acid
What are secondary alcohols oxidised to form?
Ketones
