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Flashcards in 4C - Haloalkanes Deck (26):

Mechanism for the hydrolysis of bromoethane?

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What are CFCs and HCFCs used?

Industry e.g. for aerosoles and refridgerators


Apart from CFCs and HCFCs what else contributes to the depletion of the ozone layer

Nitrogen monoxide (NO) which naturally forms during lightning.


What type of bond fission is the hydrolysis of a haloalkane?

Heterolytic fission


Equations for how the ozone layer is formed?

O2 → O• + O•

O2 + O• → O3


Define electronegativity

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond


Regarding the depletion of the ozone layer due to CFCs. What role does the Cl radical take in this reaction?

It's a reactive intermediate


Why do iodoalkanes have the fastest rate of hydrolysis?

They contain the most number of sheilding electrons, decreases the nuclear attraction and the energy required to break the C-I bond is the least


Give 3 examples of nucleophiles





Write an equation to show the photodissociation of CFCs in the stratosphere.

Conditions required?

What type of bond fission is this?

CF2Cl2 → CFCl• + Cl•

Condition = UV light

Homolytic fission


Equation to show the depletion of the ozone layer

O3 → O2 + O•


What does a curly arrow show in a mechanism?

The movement of an electron pair


Out of radical substitution, electrophilic addition and nucleophilic substitution:

Which has the greated atom economy?

Nucleophilic substitution = 100% atom economy (produces only one product.


-Radical substitution - Too many possible isomers and byproducts.

-Electrophilic addition - Produce isomers.




What does it stand for?

CFCs and HCFCs?

CFCs = Chlorofluorocarbons

HCFCs = Hydrochlorofluorocarbons



3 Ways of synthesising a haloalkane?

1. Free radical substitution - Alkane + Halogen

2. Electrophilic addition - Alkene + Halogen or Alkene + Hydrogenhalide

3. Nucleophilic substitution - Alcohol + hydrogenhalide


Write equations showing how NO contributes to the depletion of the ozone layer. 

Overall equation?


NO• + O3 → NO2• + O2

NO2• + O → NO• + O2


Overall equation:

O3 + O → 2O2


The rates of hydrolysis of chloroethane, bromoethane and iodoethane are different.

-Describe how you would monitor the reaction rates.

-Explain why the different haloalkanes react at different rates.

(8 marks)

-Add 3 drops of each haloalkane into a test tube. Lable them accordingly.


-Add 1cm3 of ethanol to each of these 3 test tubes. The ethanol acts as a co-solvent


-Get 3 new test tubes. Add 1cm3 of aqueous AgNO3 to each of them. Place these 3 test tubes into a hot water bath. Hot water bath ensures that a constant temperature is maintained throughout experiment.


-Add one test tube of the aqueous AgNO3 to each of the test tubes containing the haloalkanes and ethanol.


-Place the 3 test tubes into the hot water bath. Heat from hot water bath will provide heat to speed up the rate of the reaction.


-Use stop watch to time how long it takes for a coloured precipitate to form (this is the silver halide precipitate).


-Equation for hydrolysis (X = halogen):

CH3CH2X + H2O → CH3CH2OH + X-


-Equation for precipitation reaction:

Ag+ + X- → AgX


Iodoethane reacted the fasted, chloroethane reacted the slowest. The strength of the C-X bond affects the reactivity of the haloalkane. C-I bond is the weakest of the 3 C-X bonds and so iodoethane had the fastest rate of reaction.


What does the ozone layer protect us from?

UV radiation - over exposure increases chance of developing skin cancer


Define nucleophile

An atom (or group of atoms) which is attracted to an electron deficient center or atom, where it donates a pair of electrons to form a new covalent bond.


Where is the ozone layer found?



Preperation of an alchohol by hydrolysis of a haloalkane:

-Name reagent used


Reagent = Aqueous NaOH

Conditions = Heat under reflux

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Radical mechanism for the depletion of the ozone layer due to CFCs


Overall equation?

Conditions = UV light



CF2Cl2 → CFCl• + Cl•



Cl• + O3 → ClO• + O2

ClO• + O → Cl• + O2


Overall equation:

O3 + O → 2O2


Why do organic reactions often require heating under reflux?

Organic compounds have a simple molecular structure so they ahve low boiling points. In order to keep the contents of the flask from boiling dry you need to heat the mixture under reflux.


Order of rate of hydrolysis of chloro-, bromo- and iodoalkanes?

Iodoalkanes = Fastest


Chloroalkanes = Slowest


Why do you think haloalkanes are generally more reactive than alkanes?


Why is this not the case for fluoroalkanes?

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Carbon-Halogen bond is weaker than the C-H bond which means that they require less energy to break so they can react more easily.


C-F bond is stronger than the C-H bond so the C-F bond requires more energy to break, therefore  fluoroalkanes are less reactive than alkanes.


In CFCs why does the C-Cl bond break instead of the C-F bond?

The C-F bond is stronger than the C-Cl bond