HaloAlkanes

Question 1

What is a halogenoalkane?

Answer 1

A saturated hydrocarbon with a halogen bonded to at least one carbon

Question 2

Name a given halogenoalkane

Answer 2

Chloromethane

Question 3

What explains halogenoalkanes increased reactivity relative to alkanes?

Answer 3

The polar carbon-halogen bond

Question 4

Why do halogenoalkanes contain polar bonds?

Answer 4

Due to the difference in electronegativity between carbon and halogens

Question 5

What kind of reactions do halogenoalkanes undergo?

Answer 5

Nucleophilic substitution

Question 6

What is a nucleophile

Answer 6

A substance with a lone pair of electrons

Question 7

Which three nucleophiles do halogenoalkanes react with?

Answer 7

OH⁻, CN⁻ and NH₃

Question 8

What reagents and conditions are necessary for hydroxyl substitutions of halogenoalkanes?

Answer 8

Reflux in aqueous solution of NaOH

Question 9

What reagents and conditions are necessary for nitrile (cyanide) substitution of halogenoalkanes?

Answer 9

Aqueous, alcoholic KCN

Question 10

What is the importance of nucleophilic substitution with cyanide ions?

Answer 10

Increases the length of the carbon chain

Question 11

What reagents and conditions are necessary for ammonia substitution of halogenoalkanes?

Answer 11

Reflux in aqueous, alcoholic excess ammonia

Question 12

Why is excess ammonia required in its nucleophilic substitution with a halogenoalkane?

Answer 12

To prevent further substitutions

Question 13

Draw a nucleophilic substitution mechanism for a given halogenoalkane reacting with a given nucelophile

Answer 13

CH3Cl + HCN- -> CH3CN + HCl

Question 14

How is the rate of reaction dependent on the enthalpy of the C-X bond?

Answer 14

The greater the enthalpy of the C-X bond, the greater its strength, the slower the reaction

Question 15

What is the trend in C-X reaction rates

Answer 15

Increases down the group from C-F to C-I

Question 16

What is an elimination reaction?

Answer 16

A reaction where a halogenoalkane becomes an alkene

Question 17

Which elements are “eliminated” in an elimination reaction

Answer 17

H and X

Question 18

What conditions favour elimination reactions?

Answer 18

Secondary or tertiary halogenoalkane, hot ethanolic KOH

Question 19

What is ozone?

Answer 19

O₃

Question 20

Where is ozone found and why is it beneficial?

Answer 20

Upper atmosphere, absorbs harmful UV radiation

Question 21

What is a CFC?

Answer 21

A chlorofluorocarbon: a compound containing C-Cl and C-F bonds

Question 22

What were CFCs used for?

Answer 22

Refrigerants and solvents

Question 23

What happens to CFCs when exposed to UV?

Answer 23

C-Cl bond breaks and generates Cl∙

Question 24

How do chlorine radicals interact with ozone?

Answer 24

Catalyse its decomposition into O₂ thus forming a “hole” in the ozone layer

Question 25

Why are CFCs now banned for use?

Answer 25

Due to research results from different groups within the scientific community

Question 26

Give two equations showing the decomposition of ozone with chlorine radicals

Answer 26

Cl∙ + O₃ → ClO∙ + O₂ , ClO∙ + O₃ → 2O₂ + Cl∙

Question 27

What is the overall equation for the decomposition of ozone?

Answer 27

2O₃ → 3O₂