Halogenoalkane ORGANIC

Question 1

What can be used to explain different reactivities of halogenoalkanes?

Answer 1

Bond energies as substitution reactions have different rates and involve breaking carbon-halogen bond

Question 2

What is meant by heterolytic fission reaction?

Answer 2

Where one atom gets both electrons from covalent bond

Question 3

What is formed when chloride reacts with aqueous silver nitrate solution?

Answer 3

White precipitate (silver chloride)

Question 4

What is formed when bromide reacts with aqueous silver nitrate solution?

Answer 4

Cream precipitate (silver bromide)

Question 5

What is formed when Iodide reacts with aqueous silver nitrate solution?

Answer 5

Pale yellow precipitate (silver iodide)

Question 6

Which halogenoalkane is most reactive in aqueous silver nitrate solution?

Answer 6

Iodide

Question 7

Which halogenoalkane is least reactive in aqueous silver nitrate solution?

Answer 7

Fluoride

Question 8

Are halogenoalkanes or alkanes more reactive? Why?

Answer 8

Halogenoalkanes are much more reactive
Due to presence of electronegative halogens

Question 9

What two types of reactions will halogenoalkanes undergo?

Answer 9

Nucleophilic substitution
Elimination

Question 10

What happens in the nucleophilic substitution reactions of halogenoalkanes?

Answer 10

A halogen is substituted for another atom or group of atoms

Question 11

What is produced in the nucleophilic substitution reactions of halogenoalkanes?

Answer 11

Alcohols, amines, nitriles

Question 12

What happens in the elimination reactions of halogenoalkanes?

Answer 12

Hydrogen halide is eliminated during reaction

Question 13

What is produced in the elimination reactions of halogenoalkanes?

Answer 13

Alkene

Question 14

What is the nucleophile in the formation of alcohols?

Answer 14

Hydroxide

Question 15

What is the aqueous solution used for formation of alcohols?

Answer 15

Sodium hydroxide
Potassium hydroxide with ethanol

Question 16

What type of reaction is the formation of alcohol?

Answer 16

Hydrolysis

Question 17

What determines rate of reaction in the formation of alcohols? How?

Answer 17

Type of halogen in halogenoalkane
Stronger the C-X bond, slower reaction

Question 18

Why is hydroxide better than water as nucleophile in formation of alcohol?

Answer 18

Full negative charge instead of partial

Question 19

What can be used to measure the rate of hydrolysis of halogenoalkanes?

Answer 19

Acidified silver nitrate

Question 20

Describe how acidified silver nitrate is used to measure the rate of hydrolysis of halogenoalkanes.

Answer 20

Set up three test tubes in 50ᵒC water bath with mixture of ethanol and acidified silver nitrate
Add few drops of chloroalkane, bromoalkane and iodoalkane to each test tube and start timer
Time how long for each precipitate to form

Question 21

What is formed in reaction between chloroalkane and acidified silver nitrate?

Answer 21

White precipitate

Question 22

What is formed in reaction between bromoalkane and acidified silver nitrate?

Answer 22

Cream precipitate

Question 23

What is formed in reaction between iodoalkane and acidified silver nitrate?

Answer 23

Yellow precipitate

Question 24

What conclusions can be made from reaction between halogenoalkanes and acidified silver nitrate?

Answer 24

Yellow precipitate forms fastest as C-I bond has lowest bond enthalpy so easiest to break
White precipitate will form slowest as C-Cl bond has highest bond enthalpy so hardest to break

Question 25

What is the nucleophile in the formation of nitriles?

Answer 25

Cyanide

Question 26

What happens in nitrile formation?

Answer 26

Ethanolic solution of potassium cyanide is heated under reflux with halogenoalkane

Question 27

What is significant about nuclephilic substitution of halogenoalkanes with KCN?

Answer 27

Adds extra carbon atom to carbon chain

Question 28

What is the nucleophile in formation of primary amines?

Answer 28

Ammonia

Question 29

What happens in formation of primary amine?

Answer 29

An ethanolic solution of excess ammonia is heated under pressure with halogenoalkane

Question 30

What is lost in halogenoalkane elimination reactions?

Answer 30

A hydrogen halide

Question 31

What happens in halogenoalkane elimination reaction?

Answer 31

Halogenoalkanes heated with ethanolic sodium hydroxide causing C-X bond to break heterolytically forming X- ion and leaving alkene as organic product

Question 32

What is the result of an elimination reaction using NaOH (hot, in ethanol)?

Answer 32

Alkene

Question 33

What is the result of an elimination reaction using NaOH (warm, aqueous)?

Answer 33

Nucleophilic substitution Alcohol produced

Question 34

What are the most common halogenoalkanes?

Answer 34

Chlorofluorocarbons

Question 35

What are chlorofluorocarbons?

Answer 35

Compounds containing carbon atoms with chlorine and fluorine atoms attached

Question 36

What properties do chlorofluorocarbons (CFCs) have which make them useful?

Answer 36

Chemical inertness Non-flammable Non-toxic

Question 37

State three uses of CFCs.

Answer 37

Refrigerators Propellants for aerosols Solvents for dry cleaning

Question 38

Why is the ozone layer beneficial?

Answer 38

Absorbs most of suns harmful UV radiation

Question 39

Why is UV radiation bad?

Answer 39

Linked to skin cancer, damaging DNA and harming marine life

Question 40

How do CFCs effect ozone layer?

Answer 40

CFCs absorb lots of UV radiation in upper atmosphere CFCs are broken down by UV light to form chlorine radicals Chlorine radicals react with and break down ozone layer

Question 41

Why are HFCs often used instead of CFCs?

Answer 41

Don't contain chloride atoms so no adverse affects on ozone layer

Question 42

What are hydrofluorocarbons (HFCs)?

Answer 42

Compounds that contain a carbon attached to hydrogen and fluorine atoms only Chemically inert like CFCs