haloalkanes Flashcards
Compare the reactivity of e.g. chloroalkane to bromoalkane in nucleophilic substitution
- Bromoalkane is more reactive than chloroalkane
- C-Br bond is weaker than C-Cl bond (C-X bond gets weaker down the group)
- Less energy is needed to break the C-Br bond
define nucleophile
electron pair donor
problem with combustion of polymers such as pvc
HCL toxic gas produced
why is it important for the concentration of the ozone in the stratosphere maintained?
protects against UV radiation
which causes skin cancer cells
suggest the formula of a compound that can be used as a refrigerant instead of CCl2F2
HFC
HCFC
balanced equation for the depletion of the ozone
03 + 0 = 202
role of Cl in depletion of the ozone
acts as a catalyst
gets used up then regenerated
why is the C-halogen bond polar?
because halogen atom is more electronegative than carbon atom
4 examples of nucleophiles
ammonia
water
hydroxide
cyanide
define a hydrolysis
A chemical reaction involving water or an aqueous solution of a hydroxide ion, that causes the breaking of a bond
reagents and conditions of nucleophillic substitution
R=NaOH(aq)
C=heat under reflux
what does heating under reflux involve?
importance?
continuous boiling and condensing of a liquid
prevents loss of evaporation
not boiling dry
what type of bond fission is nucleophillic substitution?
heterolytic
what does a curly arrow show?
movement of an electron pair to make or break a covalent bond
how is the rate of hydrolysis of primary alcohols meassured?
R= silver nitrate(aq) to test for halides
C=ethanol solvent and heat in a water bath
The ethanol (solvent) is needed to mix together the aqueous silver nitrate and the haloalkane
method for rate of hydrolysis of primary alcohols
Incubate a set amount of haloalkane in a test tube in a water bath at 50oC
Place a set amount of ethanol and aqueous silver nitrate in another test tube in a water bath at 50oC
Mix the liquids together in one test tube and replace in the water bath at 50oC
Measure the time taken for a precipitate to form
Rate of hydrolysis reaction = 1 / time
reagents and conditions of reaction of a haloalkane and a cyanide ion
R= NaCN or KCN
C=dissolved in ethanol
why is the CN ion dissolved in water instead of ethanol?
water would react with the haloalkane in the hydrolysis reaction.
Why can ammonia behave as a nucleophile?
It has a lone pair of electrons which can be donated
uses of halogen compounds
-polymers e.g. PVC, PTFE for non-stick pans
-as CFC chlorofluorocarbonsw
why were CFCs used?
as inert, non-flammable and non-toxic
used as propellants, refrigerants and solvents for dry cleaning
why are CFCs no longer used?
catalyse depletion of the ozone layer
what replaced CFCs
HFCs hydrofluorocarbons
what is the ozone layer?
Ozone, O3 , is in the stratosphere (upper atmosphere) and absorbs most of the Sun’s UV radiation.
What is the effect of the depletion of Ozone in the Ozone Layer?
Ozone absorbs the Sun’s harmful UV radiation.
If there is less ozone in the ozone layer, there is less protection against the UV radiation, causing a rise in skin cancer / eye cataracts.
Explain why ozone depletion should be of major concern to humans.
Ozone absorbs the Sun’s harmful UV radiation
More UV radiation leads to a rise in skin cancer
