3.3.3 Halogenoalkanes Flashcards
What is a nucleophile
It is a chemical species that donates an electron pair to form a chemical bond
Which nucleophiles do you need to know the substitution reactions with
OH-
CN-
NH3
is a carbon halogen bond polar or non-polar
polar
why are carbon halogen bonds polar
and charges
halogens are more electronegative than carbon, and electrons are closer to halogens
the halogen is negative, and the carbon is positive
What colour precipitate does chlorine form
White
What colour precipitate does bromine form
Cream
What colour precipitate does iodine form
Yellow
What is the most common halogenalkanes
Chlorofluorocarbons
Uses of CFCs
Refrigerators
Solvents for dry cleaning
Why do CFCs have many uses
Due to their chemical inertness they are non-flammable & non-toxic
How do CFCs cause the destruction of the ozone layer (3 steps)
CFCs absorb lots of UV radiation in upper atmosphere
CFC are broken down by UV light causing formation of chlorine radicals
The radicals react with ozone and break the layer down
Do paper flash cards for mechanisms
Do it
What is used in elimination reaction
Heated under ….. with…..
Reflux
Sodium/potassium hydroxide dissolved in ethanol
In elimination the hydroxide is acting as a. + why
Base
It is excepting a proton
Equation to show how chlorine catalyses decomposition of the atmosphere
CCl3F + he —> *CCl2F + *Cl
Cl* + O3 —-> ClO* + O2
ClO* + O3 ——> 2O2 + Cl*
*cl + *Cl —Cl2
Why do halogenalkanes have a high boiling point ( than alkanes)
They have Van deer Waals forces but because polarity of carbon halogen bond there are also permanent dipole dipole forces
As we go down group 7 the boiling point of halogenalkanes ….. and why
Increases
Number of electrons increases this means greater Van deer Waals forces
Halogenalkanes are soluble/insoluble + why
Insoluble can’t form hydrogen bonds
They are soluble in non polar
Elimination hydroxide ion conditions why
Solution of hydroxide ions
Ethanol to solubilise the haloalkane so it can react with aqueous hydroxide ions
Heat under reflux increase rate of reaction
(Halogenalkanes insoluble in water so would not react with the dissolved hydroxide ions)
What type of reaction is nucleophilic substitution with hydroxide ion
Hydrolysis
What happens during the rate of hydrolysis practical
The water reacts with the halogenalkanes by nucleophilic substitution and the halide ion is released
Halide ion reacts with silver ion to form precipitate
Order of reactions for hydrolysis of hydrogenalkanes practical + why
Iodine then bromine then chlorine
The bond enthalpy increases lots of energy needed longer time
Why when doing nucleophilic substitution do we use an excess of ammonia
The product amine still has a lone pair of electrons on the nitrogen
so it can act as a nucleophile and react with haloalkane
Excess ammonia more likely to react with haloalkane
What reactions should happen in the ozone layer without CFCs
O2 —> *O + *O (UV light needed)
O2 + *O —> O3
Define free radical
Any species with an unpaired electron
Give two equations to show how chlorine radicals catalyse the decomposition of the ozone
Cl* + O3 —> ClO* + O2
ClO* + O3 —> Cl* + 2O2
What determine reactivity of halgeonalkanes
Bond enthalpy
Halogenalkanes get more reactive going …
Down the group
Why is water used rather than hydroxide ion
Hydroxide ions would react with silver to form insoluble silver hydroxide
What are the 3 steps for makinga cyclohexene
Distillation
Seperation
Purification
Why are anti-bumping granules used
To prevent bubbling
What do we use to heat a round bottom flask in the distillation step
Heating mantle
Why do we use a heating mantle and not a bunsen burner
Cyclohexanol is flammable
How to purify when making cyclohexene
Add anhydrous CaCl2. This dehydrating agent will remove any aqueous substance. Invert and leave
How are alcohol produced
Hydration alkenes
Conditions for hydration of alkenes
Use steam and acid catalysts
Temperature 300 and 60 atm
Is fermentation endo or exothermic
Exothermic
Advantages of biofeuls
Renewable
Carbon neutral
Disadvantages biofeuls
Expensive
Takes up land that could be used for farming
What is used for oxidation of alchols +more info
Acidified potassium dichromate
Turns from orange to green
What are primary acids oxidised to
Aldehydes then carboxylic acids
What a secondary oxidised to
Ketones
What are teritary alcohols oxidised to
Nothing
How do we oxidise alcohols
Distillation then reflux
In the industrial process of making an alcohol from an Alkene is a catalysts used
Yes
Acid catalyst E.g. phosphoric acid
Role of ammonia in nucleophilic substitution
Nucleophile
Then a base
Hydroxide ion acts as x2 in which
Elimination = base
Substitution = nucleophilic
In chlorofluorocarbons which bind is easier to break and why
C-cl lower bond enthalpy
Overall equation destruction of ozone
2O3 —> 3O2
