organic chemistry- haloalkanes

Question 1

why is the carbon-halogen bond in a haloalkane polar?

Answer 1

because halogen atoms are more electronegative as the electron pair is closer than to the carbon atom. The slightly positive charge on the carbon attracts species containing a lone pair of electron.

Question 2

what are nucleophiles?

Answer 2

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

Question 3

what happens when a nucleophile reacts with a haloalkane?

Answer 3

nucleophile replaces halogen atom in a substitution reaction. A new compound is formed containing a different functional group. The reaction mechanism is nucleophilic substitution.

Question 4

what is hydrolysis?

Answer 4

a chemical reaction involving water or an aqueous solution of hydroxide which causes the breaking of a bond in a molecule.

Question 5

how does a hydrolysis reaction occur in a haloalkane?

Answer 5

halogen atom is replaced by -OH group which is an example of nucleophilic substitution.

Question 6

Describe the steps involved in the hydrolysis of haloalkanes?

Answer 6

1)the nucleophile, OH-, approaches delta positive carbon on the opposite side of the halogen atom which minimises repulsion.
2)lone pair of electron is attracted and donated to the carbon atom. A new bond is formed.
3)carbon-halogen bond breaks in heterolytic fission. Halide ion and new alcohol compound is formed.

Question 7

Can haloalkanes be converted into alcohols using aqueous sodium hydroxide.

Answer 7

Yes, but the reaction is very slow at room temperature so it is heated under reflux to obtain a good yield of product

Question 8

what does the rate of hydrolysis on haloalkanes depend on mainly?

Answer 8

the strength of the carbon-halogen bond. Compounds with the slower rate of reaction have stronger carbon-halogen bonds.

Question 9

which halogen has the strongest to least strong halogen bond? (Cl,Br,I)

Answer 9

1)most strong: carbon-chlorine bond (slowest rate)
2) carbon-bromine bond
3)least strong: carbon-iodine bond (fastest rate)

Question 10

what is the other factor of the rate of hydrolysis of haloalkanes?

Answer 10

it structure depending if it is tertiary, secondary or primary. Primary structures are the slowest and tertiary structures are the fastest. This is because the teriary structure has a greater stability of carbocation and it has a two step mechanism.

Question 11

what are organohalogen compounds?

Answer 11

compounds that contain at least one halogen atom joined to a carbon chain. They are rarely found naturally and are not broken down naturally. They are used in pesticides, refrigerants and solvents.

Question 12

where is the ozone layer found?

Answer 12

outer edge of stratosphere.

Question 13

How does the ozone layer protect earth?

Answer 13

by absorbing ultraviolet radiation from the sun which can cause genetic damage and skin cancer in humans.

Question 14

what happens in the ozone layer usually?

Answer 14

-ozone is continually formed and broken by uv radiation. Oxygen molecules break down into oxygen radicals.
-a steady state is then set up involving O2 and oxygen radicals which forms O3 in a reversible reaction where formation and breaking down is at the same rate.

Question 15

where are CFCs found?

Answer 15

aerosol propellants, refrigerants and air conditioning units. They are very stable due to the strong carbon-halogen bond.

Question 16

how do CFCs damage the ozone layer?

Answer 16

CFCs begin to breakdown into chlorine radicals which catalyses the breakdown of the ozone layer when reaching the atmosphere.

Question 17

how do CFCs form chlorine radicals?

Answer 17

UV radiation in the stratosphere provides enough energy to break the C-Cl bonds through homolytic fission. Since radiation initiates the process is called photodissociation of CF2Cl2.

Question 18

how does a chlorine radical breakdown the ozone layer into oxygen?(propagation steps)

Answer 18

propagation step 1: Cl. + O3 forms ClO. + O2
propagation step 2: ClO. + O forms Cl. + O2
overall equation: O3 + O forms 2O2
chain reaction

Question 19

what other radicals catalyse breakdown of ozone layer?

Answer 19

nitrogen oxide radicals from lightning strikes and aircraft travel in stratosphere.

Question 20

How do nitrogen oxide radicals breakdown the ozone layer?(propagation steps)

Answer 20

propagation step 1: NO. + O3 forms NO2. + O2
propagation step 2: NO2. + O forms NO. + O2
overall equation is the same as CFCs

Question 21

what are the properties of CFCs?

Answer 21

-very volatile
-chemically stable
-chemically stable
-non-flammable

Question 22

Describe how to monitor the hydrolysis of haloalkanes

Answer 22

-add 1cm cubed of ethanol and two drops of haloalkane to test tube
-stand test tube in water bath at 60 degrees
-place test tube containing 0.1mol/dm cubed of silver nitrate in water bath to reach a constant temperature.
-ad. 1cm cubed of silver nitrate quickly to the test tube and immediately start stop watch.
-observe test tubes and record time taken for precipitate to form

Question 23

what observations are made when observing chloro, bromo and iodo haloalkanes?

Answer 23

chloroalkane- white precipitate forms
bromobutane- cream precipitate
iodobutane- yellow precipitate

Question 24

why are people still worried about ozone depletion despite CFCs being illegal? (2 marks)

Answer 24

-CFCs are still being used
-other substances still cause ozone depletion

Question 25

why is the organic product likely to be an aldehyde when distillation is used?

Answer 25

aldehydes are most volatile/ partial oxidation and has a boiling point less than 60 degrees

Question 26

explain why product is likely to be carboxylic acid in reflux conditions? (2marks)

Answer 26

product cannot escape and complete oxidation will be achieved.

Question 27

how does a precipitate occur from hydrolysis of primary haloalkanes?

Answer 27

negative halide ions react will positive silver ions forming a precipitate of silver halide.

Question 28

are haloalkanes soluble in water?

Answer 28

no

Question 29

why is ethanol solvent used in the hydrolysis of haloalkanes?

Answer 29

ethanol allows water in the aqueous silver nitrate to mix with the haloalkane and produce a single solution.

Question 30

greenhouse effect is dependant on what?

Answer 30

-abundance of greenhouse gases in atmosphere
-atmospheres ability to absorb UV rays

Question 31

what happens to bonds when UV radiation is absorbed?

Answer 31

it vibrates

Question 32

what are CCSs?

Answer 32

they react with carbon dioxide to form metal oxides they can reduce global warming in the atmosphere but they are also used in deep in the ocean

Question 33

what is the chemical test and observation of a haloalkane?

Answer 33

test- silver nitrate and ethanol and warm in 50 degrees water bath
observation- chloroalkane: white precipitate
bromoalkane: cream precipitate
iodoalkane: yellow precipitate