Halogenoalkanes

Question 1

Define halogenoalkane

Answer 1

A homologous series where one or more hydrogen atoms in an alkane have been replaced by a halogen atom.

Question 2

Define primary halogenoalkane

Answer 2

Primary halogenoalkanes have their halide ion joined to a carbon that is itself attached to no other or one
other carbon.

Question 3

Define secondary halogenoalkane

Answer 3

Secondary halogenoalkanes have their halide ion joined to a carbon that is itself attached to 2 other carbon.

Question 4

Define tertiary halogenoalkane

Answer 4

Teritary halogenoalkanes have their halide ion joined to a carbon that is itself attached to 3 other carbon.

Question 5

Define hydrolysis

Answer 5

A reaction in which a molecule is broken down by its reaction with water.

Question 6

Name the reactions of halogenoalkanes

Answer 6

Elimination Reactions
Nucleophilic substituition

Question 7

What is the general formula of halogenoalkanes?

Answer 7

CnH2n+1X

Question 8

Describe the process of elimination reactions

Answer 8

1.Dissolve a alkali in ethanol to avoid hydrolysis
2. the hydrogen halide is acidic and will be neutralised by the alkali (NaOH)

Question 9

Describe the process of monitoring the rate of hydrolysis using sodium hydroxide

Answer 9

1. Add halogenoalkane to excess NaOH
   2.Neutralise NaOH with HNO3(Nitric Acid)
   3.Add AgNO3 and monitor the density of the precipitate formed
   The faster the reaction, the denser the precipitate formed

Question 10

Describe the process of monitoring the rate of reaction using water

Answer 10

1.Add halogenoalkane to water
2. Add AgNO3 to solution with a small volume of ethanol to allow hydrolysis to occur
3. A precipitate will form- time this to detemine the rate of silver halide production

Question 11

Describe what happens to CFCs in the atmosphere

Answer 11

Initiation-Photochlorination, c-cl bond is weakest so breaks first
CFCl3 → Cl· + CFCl2·
Propagation- Cl radicals decompose ozone molecules
Cl· + O3 → ClO· + O2
ClO· + O3 → Cl· + 2O2
Termination- 2 Radical react together

Question 12

What are the uses of halogenoalkanes?

Answer 12

*Solvents-Dry cleaning fluids, polar but are not soluble in water
*Refrigerants-low boiling point so evaporate cooling the surrounding enviroment down.
*Anaesthetics-trichloromethane(CHCl3), Halothane(HClBrCl3)
*DDT- Insecticide
*Thyroxine- Thyroid Hormone

Question 13

Define an elimination reaction

Answer 13

A reaction that involves the loss of a small molecule in order to produce a double bond.

Elimination reactions in halogenoalkanes involves the removal of a hydrogen halide and the formation of an alkene.

Question 14

What is the order of reactivity of the levels of halogenoalkanes?

Answer 14

Teritary> Secondary> Primary

Question 14

What are the conditions required for a hydrolysis reaction of a halogenoalkane?

Answer 14

*Heat under refulx
*Sodium/Potassium Hydroxide

Question 14

Describe the process of nucleophilic substituition

Answer 14

1.Hydrolysis provides OH- ion
2.The halogen has a higher electronegativity than the carbon producing a polar bond and attracking an nucleophile.
3.The OH- aproaches the carboncation and donates its lone pair of electrons forming a new covalent bond and replacing the bromine atom.
4. Walden inversion occurs