Alcohols

Question 1

What is does an alcohol contain in its name if it has 2 or 3 OH groups?

Answer 1

2 OH groups is -diol
3 OH groups is -triol
E.g. pentan-3,4-diol

Question 2

Why are alcohols soluble and how does chain length affect it?

Answer 2

• dissolve in water as have hydrogen bonds between polar -OH group and the water molecules.
• the more OH groups the more soluble the alcohol as it forms more Hydrogen bonds
• Solubility decreases as chain length increases as more hydrocarbons present which can’t form Hydrogen bonds with the water molecules
• more branched is less soluble as less IDD

Question 3

What boiling point and volatility of alcohols?

Answer 3

Hydrogen bonds cause alcohols to have a lower volatility than alkanes .e.g. ethanol has lower volatility than ethane
- Hydrogen bonds between alcohol molecules cause alcohols to have a higher boiling point than expected (strong intermolecular, more OH groups=higher BP.)
- low volatility=high bp

Question 4

Whats equation for complete combustion of alcohols?

Answer 4

E.g.
CH4O(l) + 11/2O2 (g) —> CO2(g) + 2H20 (l)

Question 5

What are the suitable mixtures for oxidation of alcohols and what would you observe?

Answer 5

Primary/secondary alcohols oxidised by oxidising agents.
Suitable oxidising agent contains acidified dichromate ions(H+/Cr2O7-2)
Oxidising mixture made from potassium dichromate(K2Cr2O7) and sulfuric acid (H2SO4)
During reaction, the acidified potassium dichromate changes from orange to green.

Question 6

Whats initial oxidation of primary alcohols produce?

Answer 6

Distilled to produce aldehyde.
E.g.
C3H8O + [O] —> C3H6O + H2O
Need to know apparatus set up

Question 7

What does complete oxidation of primary alcohols produce?

Answer 7

Under reflux to produce Carboxylic acid.
E.g.
C3H8O + 2[O] —> C3H6O2 + H2O
It ensures that contents of flask don’t boil dry
need to know apparatus set up

Question 8

What are secondary alcohols oxidised to form?

Answer 8

Under reflux to produce ketone.
Further oxidation doesn’t occur
E.g.
C3H8O + [O] —> C3H7O + H2O

Question 9

What do tertiary alcohols produce in oxidation?

Answer 9

Tertiary alcohols resistant to oxidation
Dichromate solution remains orange.

Question 10

What are alcohols dehydrated to and what are the suitable catalysts?

Answer 10

Dehydrated to form alkenes in presence of an acid catalyst.
Example of an elimination reaction.
Acid catalysts: Concentrated Phosphoric acid (H3PO4) or Concentrated Sulfuric Acid (H2SO4)
The alcohols heated under reflux.

Question 11

Whats the definition of dehydration?

Answer 11

The removal of a molecule from a saturated molecule to make an unsaturated molecule.

Question 12

What do alcohols produce when they react with hydrogen halides (substitution reactions of alcohols)?

Answer 12

React with hydrogen halides to form haloalkanes.
Alcohol heated under reflux with sulfuric acid and a sodium halide.
Sodium halide and sulfuric acid react together to form a hydrogen halide which reacts with alcohol.
E.g. 2 reactions take place
1) formation hydrogen halide: NaBr + H2SO4 —> NaHSO4 + HBr
2) hydrogen halide reacts with the alcohol: C4H10O + HBr —> C4H9Br + H2O