Chapter 14 - Alcohols Flashcards
Why do alcohols have higher melting points than alkanes?
The intermolecular forces between non-polar molecules (e.g. alkanes) are very weak London forces.
Alcohols have a polar O-H bond because of the difference in electronegativity of the oxygen and hydrogen atoms. The intermolecular forces will be very weak London forces but there will also be much stronger hydrogen bonds between the polar O-H groups.
Why are alcohols less volatile than alkanes?
In the liquid state, intermolecular hydrogen bonds hold the alcohol molecules together. These bonds must be broken in order to change the liquid alcohol into a gas. This requires more energy than overcoming the weaker London forces in alkanes.
Why are alcohols soluble in water?
Alcohols are completely soluble in water as hydrogen bonds form between the polar -OH group of the alcohol and water molecules.
Alcohols become less soluble as chain length ________.
Alcohols become less soluble as chain length increases.
What are primary alcohols?
Alcohols in which the -OH group is bonded to a carbon atom that is bonded to one other carbon atom.
Despite this, methanol is a primary alcohol.
What are secondary alcohols?
Alcohols in which the -OH group is bonded to a carbon atom that is attached to 2 other carbon atoms.
What are tertiary alcohols?
Alcohols in which the -OH group is bonded to a carbon atom that is bonded to 3 other carbon atoms.
Primary alcohols can be oxidised to form either…
…aldehydes (by distillation) or carboxylic acids (under reflux).
The product of the oxidation depends on the reaction conditions used because aldehydes are themselves also oxidised to carboxylic acids.
Describe the process of dehydration of alcohols.
An alcohol is heated under reflux in the presence of an acid catalyst such as concentrated H2SO4 to form an alkene.
Alcohol → Alkene + Water
Secondary alcohols can be oxidised to form…
…ketones under reflux.
What is the colour change observed during the oxidation of alcohols?
Orange → Green
What is a common oxidising agent used in the oxidation of alcohols?
Acidified potassium dichromate (VI)
K2Cr2=7 / H2SO4
Describe the process of halide substitution of alcohols.
NaX + H2SO4 (catalyst) → HX
Alcohol + HX → Haloalkane + Water
