chapter 15

Question 1

haloalkanes

Answer 1

compounds containing the elements carbon, hydrogen and at least one halogen atom

Question 2

substitution reaction

Answer 2

a reaction in which one atom or a group of atoms is replaced by another atom or a group of atoms

Question 3

in the hydrolysis of a haloalkane, the halogen atom is replaced by an …………… group to form an alcohol

Answer 3

OH

Question 4

the hydrolysis of haloalkanes occurs under………………..

Answer 4

reflux

Question 5

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?

Answer 5

to minimize repulsion between the halogen atom and the nucleophile, as they are both negative

Question 6

the rate of hydrolysis of haloalkanes depends on the

Answer 6

strength of the carbon-halogen bond

Question 7

organize these bonds in terms of strength(in ascending order)
Iodoalkanes
bromoalkanes
chloroalkanes
fluoroalkanes

Answer 7

iodoalkanes
bromoalkanes
chloroalkanes
fluoroalkanes

Question 8

the stronger the carbon-halogen bond in a haloalkane, the ……………………. it reacts, because ……………… energy is required to break these bonds

Answer 8

slower
a lot of

Question 9

fluoroalkanes are unreactive, true or false

Answer 9

true

Question 10

what happens to the rate of hydrolysis of haloalkanes as the Carbon-Halogen bond strength increases

Answer 10

decreases

Question 11

how do we experimentally measure the rate of hydrolysis of primary haloalkanes

Answer 11

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

Question 12

in the experimental effort to measure the rate of hydrolysis of haloalkanes, why do we add ethanol to the test tubes

Answer 12

it acts as the bridging solvent, as haloalkanes are not soluble in water

Question 13

in the experimental effort to measure the rate of hydrolysis of haloalkanes, what observations do we make

Answer 13

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

Question 14

function of ozone

Answer 14

it absorbs the biologically damaging high-energy UV radiation (UV-B)

Question 15

where is the ozone layer found

Answer 15

at the outer edge of the stratosphere

Question 16

effects of exposure to UV-B

Answer 16

causes sunburn
could cause skin cancer
could cause genetic damage

Question 17

processes that take place in the formation of Ozone in the atmosphere

Answer 17

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

Question 18

CFCs full name

Answer 18

chlorofluorocarbons

Question 19

CFCs are stable compounds due to?

Answer 19

the strength of the carbon-hydrogen bonds

Question 20

when do CFCs break down, and why

Answer 20

when they reach the stratosphere
because of the presence of high-energy UV radiation

Question 21

CFCs break down to form?

Answer 21

chlorine radicals

Question 22

functions of the chlorine radicals formed from the breakdown of CFCs

Answer 22

they catalyse the breakdown of the ozone layer

Question 23

describe the chlorine radical cycle

Answer 23

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

Question 24

4 ways in which we could avoid the use of CFCs and their pros and cons

Answer 24

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