Alcohols

Question 1

Alcohol Homologous Series

Answer 1

=> Saturated : only single C to C bonds
=> General formula of Cn H2n+1
=> Hydroxyl group (OH) is responsible for physical + chemical properties

Question 2

Physical Properties compared to corresponding alkanes

Answer 2

• Less volatile (tendency to evaporate)
• Higher boiling point
• Greater water solubility
  => All explained by polarity

Question 3

Alkanes vs Alcohols

Answer 3

ALKANES: have non polar bonds (small diff in electronegativity of C and H) => is non-polar => intermolecular forces between non-polar molecules are v weak

ALCOHOLS: have polar O-H bonds due to (electronegativity diff between O and H) => is polar => very weak London forces but much stronger H bonds between -OH groups

Question 4

Volativity + Boiling Point

Answer 4

=> In liquid state, intermolecular H bonds hold alcohol molecule together which must be broken to (l) to (g)
=> Requires more energy compared to overcoming weaker London forces in alkanes
=> THUS alcohols have lower volativity than alkanes with the same no of carbon atoms

Question 5

Solubility In Water (and other polar solvents)

Answer 5

=> Alkanes are non polar so cant form H bond with water to dissolve
=> Alcohols are completely soluble as H bonds form between polar -OH group of the alcohol + water molecules

As the chain increases in size influence of -OH group becomes relatively smaller => solubility decreases

Question 6

Classifying Alcohols

Answer 6

Depends on number of H atoms and alkyl groups attached to the C atom that contains alcohol group

Question 7

Primary Alcohol

Answer 7

The -OH group is attached to the C w/ no mare than 1 alkyl group and 2 H atoms (methanol is the exception w/ 3 H atoms)

Question 8

Secondary Alcohols

Answer 8

The -OH group is attched to C atom that is attached to 1 H and 2 alkyl group

Question 9

Tertiary Alcohols

Answer 9

The -OH group is attached to the C atom that is attached to no H and 3 alkyl groups

Question 10

Boiling Point Trend

Answer 10

As chain lenght increases so does boiling point
=> molecule gets longer => more SA contact => stronger London forces of attraction => more energy is required to overcome them