Halogenoalkanes

Question 1

What is a halogenoalkane?

Answer 1

A species in which one or more hydrogen atoms in an alkane are replaced by a halogen.

Question 2

What makes halogenoalkanes polar?

Answer 2

The halogen being more electronegative than the carbon attached to it.

Question 3

What are the three types of halogenoalkanes?

Answer 3

Primary- Carbon that halogen attached to is attached to one carbon
Secondary- Carbon that halogen is attached to is attached to two carbons
Tertiary- Carbon that halogen is attached to is attached to three carbons

Question 4

How would you identify a halogenoalkane?

Answer 4

Heat your compound with aqueous sodium hydroxide to perform nucleophilic substitution. Then, the presence of the halogen can be viewed by adding silver nitrate (AgNO3) and HNO3.

Question 5

Why is HNO3 added in the silver nitrate test?

Answer 5

To remove excess NaOH.

Question 6

What are the results of the silver nitrate test?

Answer 6

Chlorine- white precipitate
Bromine- cream precipitate
Iodine- yellow precipitate

Question 7

What is a further test you can do to confirm the presence of halogens?

Answer 7

Adding NH3 to the precipitate formed.
Chlorine- dissolves in dilute NH3
Bromine- dissolves in concentrated NH3
Iodine- does not dissolve in NH3

Question 8

What are the conditions for nucleophilic substitution?

Answer 8

Warming the compound and adding NaOH (aq).

Question 9

What are the conditions for an elimination reaction?

Answer 9

Warm the solution, add NaOH (aq) and ethanol.

Question 10

What happens in an elimination reaction?

Answer 10

The loss of a small molecule to produce a double bond.

Question 11

Why must ethanol be added to an elimination reaction?

Answer 11

The hydrogen halide is acidic and can be removed using an alkali. To avoid hydrolysis the alkali must be in ethanol. Allow all reactants to mix.

Question 12

What is a nucleophile?

Answer 12

A chemical species that forms bonds by donating an electron pair replacing an element.

Question 13

What is a substitution reaction?

Answer 13

A reaction in which one atom or group is replaced by another.

Question 14

What are the two reactions halogenoalkanes can perform?

Answer 14

Nucleophilic substitution and elimination.

Question 15

What are the uses of halogenoalkanes?

Answer 15

They can be used as solvents, anaesthetics and refrigerants.

Question 16

Why is a reflux method used with reactions?

Answer 16

As many organic compounds are volatile and escape to the atmosphere when heated, resulting in loss of product. By cooling the vapours from the mixture the chemicals are contained within the reaction flask as they condense and run back.

Question 17

Write an ionic equation for the silver nitrate test

Answer 17

Ag+ (aq) + Cl- —> AgCl (s)

Question 18

What are CFCs?

Answer 18

Halogenoalkanes containing both fluorine and chlorine.

Question 19

What are HFCs?

Answer 19

Halogenoalkanes containing fluorine as the only halogen.

Question 20

What are some adverse environmental effects of CFCs?

Answer 20

CFCs produce chlorine radicals which create a hole in the ozone layer, which protects the earths surface from UV rays. UV enters the earth atmosphere and causes mutations in DNA which leads to skin cancer.

Question 21

What is homolytic bond fission?

Answer 21

Breaking a covalent bond between two halogens where each atom receives an unpaired electron to form two radicals.