4.5 - Haloalkanes

Question 1

Why are haloalkanes more reactive than alkanes

Answer 1

due to the electronegative halogens
the carbon - halogen bond is polar with a delta negative end on the halogen

Question 2

What 2 types of reaction can haloalkanes undergo

Answer 2

Nucleophilic substitution
Elimination reactions

Question 3

define nucleophile

Answer 3

an atom or group of atoms that is attracted to an electron deficient atom where it donates a pair of electrons to form a new covalent bond

Question 4

What is Hydrolysis

Answer 4

A Reaction involving water or an aqueous solution of hydroxide that causes the breaking of a bond in a molecule resulting in 2 products

Question 5

In the hydrolysis of a haloalkane what is formed

Answer 5

an alcohol and a halide ion

Question 6

what is hydrolysis of a haloalkane an example of

Answer 6

nucleophilic substitution

Question 7

what are the 6 stages of nucleophilic substitution

Answer 7

1. OH- approaches C atom attached to the halogen on the opposite side of the molecule from the halogen atom
   2. The direction of attack by the OH- ion minimises repulsion between the nucleophile and the delta - halogen atom
   3. A lone pair of electrons on the hydroxide ion is attracted and donated to the delta + carbon
   4. A bond is formed between the O atom and the C atom
   5. Carbon- halogen bond breaks by heterolytic fission
   6.The new organic product is an alcohol + a halide ion formed

Question 8

What does the rate of hydrolysis depend on

Answer 8

The type of halogen in the haloalkane
C-F is the strongest and doesn’t react
C-I is the weakest and has a fast rate of reaction

Question 9

what other substance can you mix a haloalkane with to undergo hydrolysis

Answer 9

water with AgNO3

Question 10

How do you test the rate of Hydrolysis

Answer 10

add acidified silver nitrate and ethanol to 3 test tubes in a 50˚c water bath
add a few drops of a chloroalkane, bromoalkane and iodoalkane to each test tube
time how long it takes for each to form a precipitate - halide ions
white - Cl
cream - Br
yellow - I

Question 11

What is nucleophilic substitution

Answer 11

A reaction in which a nucleophile attacks a carbon atom which carries a partial positive charge an atom with a partial negative charge is replaced by the nucleophile

Question 12

What are 3 uses of CFCs

Answer 12

Refrigerators
propellants for aerosols
solvents for dry cleaning

Question 13

what property do CFCs and HFCs both have

Answer 13

they are inert - not chemically reactive.

Question 14

What do CFC do to the Ozone

Answer 14

they absorb a lot of UV radiation in the upper atmosphere
The CFCs are broken down by the UV light forming Cl radicals
the radicals react with the ozone and break it down

Question 15

What is the chemical reaction for chlorine radicals breaking down the ozone layer

Answer 15

Cl (rad) + O3 -> CLO(rad) + O2
CLO(rad) + O3 -> 2O2 + Cl (rad)
therefore

2O3 -> 3O2

Question 16

Why are HFC used instead of CFC

Answer 16

as they dont break down the ozone

Question 17

What is another radical which can break down the ozone layer and how is it formed

Answer 17

(rad)NO
formed:

naturally during lighting strikes
as a result of air travel in the stratosphere

direct combination of N and O at high temp in a combustion engine

Question 18

What is the chemical reaction for NO to break down ozone

Answer 18

NO(rad) + O3 -> NO2 (rad) + O2
No2(rad) + O -> NO(rad)+O2

overall
O3+O->2O2