haloalkanes Flashcards
what is hydrolysis
hydrolysis is a reaction with water or aqueous hydroxide ions that breaks a chemical compound into two compounds
what ways can hydrolysis happen with haloalkanes
- heating with silver nitrate and ethanol added
- heating under reflux with an aquous alkali eg naoh
what is the mechanism for this reaction called
nucleophillic substitution
what is a nucleophile
an ion or molecule which is strongly attracted to a region of positive charge in something else . it is an electron pair donor
draw the mechanism for bromoethane reacting with NaOH
what happens when a haloalkane reacts with a nucleophile
the nucleophile replaces the halogen in a substitution reaction
why does the halogen - carbon bond break and not one of the h-c bonds
the weakest bond breaks and because C-H bonds are very strong the halogen - carbon bond breaks
what happens to the polarity of the haloalkanes
polarity decreases down the group because electronegativity increases as atomic radius increases , electron sheilding increases and ability to gain an electron decreases
which haloalkane bond has the weakest bond enthalpy
C-I because the attraction is weaker
how can you determine the rate of hydrolysis for different haloalkanes
- the rates can be determined by heating the haloalkane with aqueous silver nitrate with ethanol added
water in the silver nitrate solution acts as a nucleophile .
and the ethanol acts as a common solvent ,. ensuring the silver nitrate and haloalkane mix together and react .
what happens as the hydrolysis reaction occurs
halide ions form . the silver nitrate reacts with it forming a precipitate of the silver halide
what is the equation for 1-chlorobutane and silver nitrate
C4H9Cl(Aq) + H20(l)–>C4H9OH + AgCl~(s)+HNO39aq)
what are organohalogen compounds
molecules that contain atleast one halogen atom joined to a carbon chain
why are organohalogen compounds of slight concern
because they are not broken down naturally in the enviroment
where is the ozone layer found
at the outer edge of the stratosphere at a height that varies of 10-40km above earths surface
what does it do which is good
it absorbs damaging uv rays from the sun (UV-B) stopping them reaching the earths surface
why is depletion of the ozone layer bad
more uv-b will reach our planet and damage genetics and cause a greater risk of skin cancer in organisms
how does uv break oxygen
O2-> 2O
how is ozone formed
O2+O<—–> O3
what are common uses of CFCs
coolants in fridges
propellants in aerosols
dry cleaning solvents
why are CFCs very stable
because of the strong C-H bonds
what decreases their stability
-being in the stratosphere forming radicals which catalyse the breakdown of the ozone layer
what are CFCs
chlorofluoro carbons (haloakanes) molecules with all their hydrogens replaced by chlorine and fluorine
why is the Cl-C bond broken first in CFCs
it has the weakest bond enthalpy
what is the initiation step for the breakdown of ozone
CCl3F(g)—> .CCl2F(g) + .Cl(g)
by uv
what are the 2 propagation steps for the breakdown of ozone
1) Cl .(g) + O3(g) —> O2(g) + ClO .(g)
2)ClO . (g)+ O (g)—> O2(g) + Cl.(g)
what is the termination step for the breakdown of ozone
Cl. (g) + Cl. (g) –> Cl2
whats the overall equation for the breakdown of ozone
2O3 <—-> 3O2
how is Cl. a cataylst
because it is reformed
what other radials destroy ozone
nitrogen oxides formed from vehicle emissions and thunder storms can destroy ozone
what is the initation equation for NO2 breakdown
NO2 (g) —> NO.(g) + O(g)
what are the two propagation steps for the breakdown of NO2
1) NO.(g) + O3(g)—>O2 +NO2.
2) NO2.(g) + O –>O2 + NO.
