Haloalkanes

Question 1

What is the general formula of haloalkanes

Answer 1

C2n H2n+1 X

Question 2

What is a haloalkane

Answer 2

An alkane with at least one halogen atom in place of a hydrogen atom

Question 3

Why is C-X polar

Answer 3

Because the halogen is more electronegative than the carbon atom

Question 4

What is a nucleophile

Answer 4

An electrophile pair donor

Question 4

What are examples of nucleophiles

Answer 4

OH-
CN-
NH3
Water is a nucleophile but reacts more slowly

Question 5

What are primary secondary and tertiary haloalkanes

Answer 5

It depends on the position of the halogen in the carbon chain. Primary has one alkyl group secondary has 2 and tertiary has 3

Question 6

What is the reaction for nucleophilic substiution

Answer 6

Haloalkane—> Alcohol

Question 7

What are the conditions for nucleophilic substitution

Answer 7

Warm/hot

Question 8

What are the reagents and type of reaction for nucleophilic substitution

Answer 8

NaOH (aqueous)
Type- Substitution

Question 9

What is the conversion for nucleophilic substitution in CN

Answer 9

Haloalkane- Nitride ( R-C(triple) N)

Question 10

What are the conditions for the reaction with CN

Answer 10

In ethanol

Question 11

What are reagents and type of reaction for CN

Answer 11

KCN/NaCN
Substitution

Question 12

How does the alcohol form during nucleophilic substitution

Answer 12

The OH- behaves as a nucleophile and has a lone pair of electrons and these are attracted and donated to the positive carbon.
Leads to the formation of a dative covalent bond between the carbon atom and the halogen atom in the OH

Question 13

How do the products form

Answer 13

The C-H bond breaks by heterolytic fission and both electrons from the bond move to the halogen forming a halide ion

Question 13

What is hydrolysis

Answer 13

A reaction with water or hydroxide ions that breaks a bond in a compound turning it into 2 compounds

Question 14

What is the hydrolysis reaction with OH-

Answer 14

CH3CH2CH2CH3X + OH- —–> CH3CH2CH2CH2OH+ X-

Question 14

What is the hydrolysis reaction with H20

Answer 14

CH3CH2CH2CH2X+ H20 ——> CH3CH2CH2CH2OH + HX

Question 15

What is the hydrolysis reaction for the halides

Answer 15

Add ethanol as the solvent is water and organic as its imissible so dont mix so the alovent allows it to mix so the reaction can occur

Question 16

Why do you add AgNO3 for the reaction

Answer 16

To form the precipitate with halide ions then heat in a water bath for a constant temperature

Question 17

How do you compare the reactivities of the halides

Answer 17

Set up 3 test tubes each containing a different haloalkane, ethanol as a solvent and silver nitrate solution
Warm the tubes in a water bath (50-60 degrees)
Time how long it takes for ppt to form
A pale yellow precipitate quickly forms with 2-iodopropane so iodoalkanes are the most reactive. Bromo alkanes react slower than iodoalkanes to form a cream precipitate and chloroalkanes form a white precipitate the slowest

Question 18

Why was a water bath used

Answer 18

To ensure all experiments are performed at the same temperature

Question 19

How can the rate of hydrolysis be found

Answer 19

By calculating 1 divided by time taken for ppt to form

Question 20

Why does it take longer for hydrolysis to take place

Answer 20

As the rate of hydrolysis increases the strength of the carbon-hydrogen bond decreases. Higher bond enthalpies mean there are stronger bonds so the energy required to break the C-X bond is greater so takes longer for hydrolysis to take place

Question 21

How do you determine the rate of hydrolysis of a haloalkane

Answer 21

As you go down group 7 the strength of the C-X bond decreases so the lower the bond enthalpy the faster the rate of hydrolysis

Question 22

How many oxygen atoms are bonded to eachother for the ozone

Answer 22

3

Question 23

Why is the ozone layer useful to humans

Answer 23

It absorbs harmful UV radiation which could cause skin cancer from the sun and converts it into heat

Question 24

What are the equations with oxygen

Answer 24

O2------>2O O2+O----->O3 (+heat) O3-------->O2+O

Question 25

How is the concentration of ozone maintained in the ozone layer

Answer 25

It is kept at equilibrium as a reversible reaction O2+O -----> O3 The rate of formation = the rate of decomposition

Question 26

What are CFCS

Answer 26

Well known haloalkanes which only contain carbon fluorine and chlorine as all the halogens have been replaced

Question 27

What were CFCS used as

Answer 27

Aerosols and cooling devices

Question 28

Why were CFCS used a refrigerants

Answer 28

They are non toxic Non flammable Very stable

Question 29

Why do CFCS only break down high in the atompshere

Answer 29

they form chlorine radicals which catalyse the breakdown of ozone

Question 30

What are 2 alternatives to CFCS

Answer 30

HCFC AND HFC

Question 31

How would the mass of a haloalkane compare with the mass of an alkane of the same carbon chain

Answer 31

Greater as the mass of a halogen is greater than the mass of a hydrogen

Question 32

How do CFS break down the ozone layer using radical substitution (initiation)

Answer 32

CFCl3---------> Cl+C*FCl2

Question 33

How do CFS break down the ozone layer using radical substitution (propagation)

Answer 33

Cl* + O3-------> ClO + O2 ClO+ O-------> Cl+ O2

Question 33

What is the overral equation for the catalysation

Answer 33

O3+ O------------> 2O2 this is the same for all ozone degradation reactions

Question 34

How are nitrogen oxides produced

Answer 34

Car and aircraft engines and thunderstorms

Question 35

What are the 2 propagation steps for nitrogen oxide

Answer 35

NO* + O3-----------> NO2* + O2 NI2* + O-------------> NO* + O2

Question 36

What is the overral equation for nitrogen oxide

Answer 36

O3+O--------->2O2

Question 37

Why are all of these reactions chain reactions

Answer 37

The radicals are used in step 1 and regenerated in step 2