Haloalkanes

Question 1

Why are fluoroalkane un reactive?

Answer 1

due to the high strength of the Carbon - Fluorine bond.
This is why the surface of some non- stick pans is covered in a fluoroalkane.

Question 2

What are the iodoalkanes the most reactive of the haloalkanes?

Answer 2

because the bond is weak and easily broken.

Question 3

What can haloalkanes be classified as?

Answer 3

primary, secondary or tertiary.

Question 4

What are primary haloalkanes?

Answer 4

The -halo group is attached to a carbon atom with at least two H atoms attached.

Question 5

What are secondary haloalkanes?

Answer 5

The -halo group is attached to a carbon
atom with only one H atom attached.

Question 6

What are tertiary haloalkanes?

Answer 6

The -halo group is attached to a carbon atom with no H atoms attached.

Question 7

What are the physical properties of haloalkanes?

Answer 7

halogen has a higher electronegativity than the carbon to which it is attached. The presence of the polar bond and the slight charges on both the carbon and the halogen results in increased intermolecular forces between molecules. It is these permanent dipole-dipole forces which must be overcome in order to melt or boil a sample. There is therefore an increase in boiling points,
melting points and density in comparison to the corresponding alkanes. Because the haloalkanes do not possess hydrogen bonding, they are often insoluble in water, although haloalkanes are more soluble in water than the corresponding alkanes and the alkenes.

Question 8

The intermolecular forces between haloalkanes are-

Answer 8

PDD

Question 9

The intermolecular forces between a haloalkanes and water would be-

Answer 9

Hydrogen bonding

Question 10

d) We would expect 2-chlorobutane to have a boiling point than butane.

Answer 10

higher

Question 11

Define the term electronegativity

Answer 11

the ability of an atom to attract electrons to a covalent bond

Question 12

What is the carbon-halogen bond of haloalkanes and what does this do?

Answer 12

haloalkanes is polar and this gives rise to its reactivity.

Question 13

what does this mean?

Answer 13

-carbon atom attracts electrons less strongly than the chlorine atom. This
makes one end of the molecule δ+ and the other end of the molecule δ-
. In this way the bond is polarised and the positive carbon atom can be attacked by negatively charged species known as nucleophiles

Question 14

What do nucleophiles have?

Answer 14

lone pair

Question 15

When does nucleophilic substitution occur?

Answer 15

a molecule is attacked by an electron pair donor and an atom or group of atoms in the molecule is replaced by the
nucleophile

Question 16

What are nucleophiles attracted to?

Answer 16

positive/ partial positive charge

Question 17

what are reactions that haloalkanes can undergo (nucleophilic substitutions)?

Answer 17

alkaline hydrolysis of a haloalkane
haloalkanes with cyanide ions
ammonia with haloalkanes

Question 18

what are the reagents and conditions for the hydrolysis of a haloalkane? and equations

Answer 18

-Sodium hydroxide aqueous/ KOH
-Warm (or reflux)
water
-CH3Cl + NaOH—>NaCl + CH3OH
reflux

Question 19

What should never be included in the mechanism?

Answer 19

The metal ion as it is a spectator ion

Question 20

what happens when haloalkanes are reacted with an ethanolic solution of sodium or potassium cyanide?

Answer 20

Nucleophilic substitution of the cyanide ion in ethanol will take place to form nitriles

Question 21

What is the source of CN- ions?

Answer 21

KCN

Question 22

Why is nucleophilic substitution with cyanide an important reaction?
IMPORTANT

Answer 22

As it extends the length of the carbon chain

Question 23

What happens when haloalkanes are treated with excess ethanolic ammonia?

Answer 23

reacts to produce the amine, aminoethane

Question 24

what are the general equations for the reaction with ammonia and haloalkanes?

Answer 24

CH3CH2Br + 2NH3—ethanol—> CH3CH2NH2 + NH4+ Br-

CH3CH2Br + NH3 —> CH3CH2NH2 + HBr
Hbr+ NH3—> NH4Br

the plus on NH4+ is the charge

Question 25

What does the reactivity of the haloalkanes depend on?

Answer 25

on the strength of the carbon halogen bond.

Question 26

What happens as we go from C-F to C-I

Answer 26

the bond enthalpies decrease (the bonds get weaker); • it becomes easier to break the carbon to halogen bond and therefore easier to lose the halide ion; • the haloalkanes become more reactive.

Question 27

what is the practical to demonstrate the rates of hydrolysis of haloalkanes (due to strength of bond)

Answer 27

haloalkane is mixed with water and aqueous ethanolic silver nitrate and placed in a water bath at 60oC. Ethanol is used as it dissolves the haloalkanes better. • The water acts as a nucleophile as it has a lone pair of electrons on its oxygen atom but it is a slow reaction. As the hydrolysis reaction occurs, the halide ion, X- is displaced. • The halide ions, X- produced react with the Ag+ ion in the silver nitrate to form a precipitate of the silver halide. Ag+ (aq) + X- (aq) → AgX (s) • By timing the first appearance of a silver halide precipitate it is possible to deduce the rate of hydrolysis.

Question 28

What are the results of the experiment?

Answer 28

1-chlorobutane Slow production of a pale white precipitate 1-bromobutane Cream precipitate produced more rapidly 1-iodobutane Immediate production of a yellow precipitate

Question 29

Why is ethanol used in the practical?

Answer 29

better solvent for the haloalkane

Question 30

What is the role of water and the practical?

Answer 30

acts as a nucleophile

Question 31

what does heating in a water bath do?

Answer 31

Increases rate of reaction

Question 32

What does the silver nitrate do?

Answer 32

produces a precipitate of the silver halide

Question 33

what are some direct applications of Haloalkanes?

Answer 33

-polymers such as polychloroethene PVC used in plastic carrier bags -Polymers such as polytetrafluoroethene, Teflon (PTFE) used for non stick pans -Chlorofluorocarbons such as CF2Cl2 and CF3Cl, used as a refrigeran

Question 34

what do CFCs do? (chlorofluorocarbons.)

Answer 34

responsible for the thinning of the ozone layer

Question 35

what does CFCs do when they reach the stratosphere?

Answer 35

CFCs absorb ultraviolet radiation, which causes photodissociation of the carbon-chlorine bonds. CF2Cl2 → CF2Cl● + ●Cl

Question 36

what is formed when the stratosphere absorbs ultraviolet radiation? and equations

Answer 36

very reactive chlorine radicals which catalyse the decomposition of ozone to oxygen Cl• + O3 —> O2 + ClO• ClO• + O —> O2 + Cl• overall: O3 + O—> 2O2

Question 37

how do nitrous oxide affect the ozone there? and equations

Answer 37

Radicals from NOx gas from thunderstorms and aircraft may also catalyse the breakdown of ozone. •NO+ O3 —>NO2 + O2 •NO2+O —> •NO + O2 overall: O3 + O—> 2O2

Question 38

What does the term radical mean?

Answer 38

a Species that has an unpaired electron

Question 39

Where is the ozone layer found?

Answer 39

In the stratosphere