chapter 15 Flashcards
haloalkanes
compounds containing the elements carbon, hydrogen and at least one halogen atom
substitution reaction
a reaction in which one atom or a group of atoms is replaced by another atom or a group of atoms
in the hydrolysis of a haloalkane, the halogen atom is replaced by an …………… group to form an alcohol
OH
the hydrolysis of haloalkanes occurs under………………..
reflux
in nucleophilic substitution reactions of haloalkanes, why does the nucleophile approach the partially positive carbon atom on the opposite side from the partially negative halogen atom?
to minimize repulsion between the halogen atom and the nucleophile, as they are both negative
the rate of hydrolysis of haloalkanes depends on the
strength of the carbon-halogen bond
organize these bonds in terms of strength(in ascending order)
Iodoalkanes
bromoalkanes
chloroalkanes
fluoroalkanes
iodoalkanes
bromoalkanes
chloroalkanes
fluoroalkanes
the stronger the carbon-halogen bond in a haloalkane, the ……………………. it reacts, because ……………… energy is required to break these bonds
slower
a lot of
fluoroalkanes are unreactive, true or false
true
what happens to the rate of hydrolysis of haloalkanes as the Carbon-Halogen bond strength increases
decreases
how do we experimentally measure the rate of hydrolysis of primary haloalkanes
Add 3-4 drops of the haloalkanes to respective test tubes
Add ethanol and silver nitrate to the test tubes
Warm the test tubes in a water bath and measure the times taken for the precipitates of silver halide to form. Record this
in the experimental effort to measure the rate of hydrolysis of haloalkanes, why do we add ethanol to the test tubes
it acts as the bridging solvent, as haloalkanes are not soluble in water
in the experimental effort to measure the rate of hydrolysis of haloalkanes, what observations do we make
for fluoroalkanes, there is no reaction
for chloroalkanes, a white precipitate of silver chloride forms very slowly
for Bromoalkanes, a cream precipitate of silver bromide forms slower than for iodoalkanes, but faster than for chloroalkanes
for iodoalkanes, a yellow precipitate of silver iodide forms rapidly
function of ozone
it absorbs the biologically damaging high-energy UV radiation (UV-B)
where is the ozone layer found
at the outer edge of the stratosphere
effects of exposure to UV-B
causes sunburn
could cause skin cancer
could cause genetic damage
processes that take place in the formation of Ozone in the atmosphere
Initially, very high-energy UV radiation breaks oxygen molecules into oxygen radicals, by homolytic fission
A steady state is then set up involving the oxygen radicals in which the ozone is constantly being formed and broken down
This is a reversible reaction, and the both reactions occur at the same time
CFCs full name
chlorofluorocarbons
CFCs are stable compounds due to?
the strength of the carbon-hydrogen bonds
when do CFCs break down, and why
when they reach the stratosphere
because of the presence of high-energy UV radiation
CFCs break down to form?
chlorine radicals
functions of the chlorine radicals formed from the breakdown of CFCs
they catalyse the breakdown of the ozone layer
describe the chlorine radical cycle
UV light hits a CFC molecule, like CFCl3, breaking off a chlorine atom and leaving CFCl2 (both as radicals)
the chlorine atom attacks an ozone molecule(O3) pulling an oxygen atom off it and leaving an oxygen molecule(O2).
the chlorine radical binds to the oxygen atom to form a chlorine monoxide radical
A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form an oxygen molecule and a chlorine radical
once free the chlorine radical is off to attack another ozone molecule and begin the cycle again
4 ways in which we could avoid the use of CFCs and their pros and cons
using hydrofluorocarbons: have no chlorine, but are expensive to manufacture
using HCFCs: breaks down more easily than CFCs but they still contain chlorine atoms which will eventually reach the stratosphere
using pump action spray dispensers
using hydrocarbons as propellants in aerosol
