09e Halogenoalkanes

Question 1

Types of halogenoalkanes

Answer 1

Primary Halogenoalkane: The carbon atom bonded to the halogen is bonded to one other carbon or alkyl group

Secondary Halogenoalkane: Carbon atom with the halogen is bonded to two other carbon or alkyl groups

Tertiary Halogenoalkane: carbon atom with halogen is bonded to 3 carbon or alkyl groups

Question 2

Physical Properties of Halogenoalkanes: Boiling Points

Answer 2

Has some amount of pd-pd FOA, therefore has a higher boiling point than its corresponding alkane.

Question 3

Reactions of Halogenoalkanes

Answer 3

Substitution:
X with OH to form alcohols
Reagent: Dilute NaOH(or KOH), heat

Elimination:
From halogenoalkane to alkene
Reagent: ethanolic KOH, heat

Question 4

Distinguishing test for halogenoalkanes

Answer 4

A. Comparing colour of AgX precipitate
1. To the halogenoalkane, add NaOH and heat, to substitute the X ion in the halogenalkane for the OH- ion.
2. Add excess dilute HNO3 to remove excess OH- so that the OH- will not react in the next step
3. Add AgNO3 and observe the colour of the precipitate
Chloroalkane: White (soluble in dilute NH3)
Bromoalkane: Cream (soluble in conc NH3)
Iodoalkane: Yellow (insoluble even in conc NH3)

B. Rate of formation of AgX precipitate
1. Chloroalkane: white ppt formed in 5-8 minutes
2. Bromoalkane: cream ppt formed in 3-5 minutes
3. Iodoalkane: yellow ppt formed almost immediately
C-X bond breaks in the reaction, and the bond energy decreases from Cl to I.

Question 5

Uses for Halogenoalkanes

Answer 5

refrigerants, fire extinguishers