Whereis it?
lflf hen an objectburns,the quantityof ashesthat remainissmaller
rt thanthe originalobjectthat wasburned.Whathappened
to the
restof the object?
Safety.Precaqtions."Donot placematches
in the sink.Usecaution
tr
Kilt @
around flames.
Procedure
1. Measurethe massof a large kitchen match. Recordthis measurement and detailedobservations
about the match.
Materials
large kitchen ntatches
laboratorybalance
lab notebook
pen
stopwatch or clock
2- carefully strike the match and allow it to burn for five seconds.
Then, blow it out. CAUTION:Keephair and looseclothing away
from the flame. Recordobservationsabout the match as it burns
and after the flame is extinguished.
3. Allow the match to cool. Measureand recordthe massof the
burned match.
4. Placethe burned match in a containerdesignatedby your instructor.
5. Repeatthis procedure.Compareyour data from the two trials.
Analysis
How do you accountfor the changein mass?Where is the matter
that appearsto have been lost?
TheSloriesof TwoEhemicals
0bjeclives
Explainthe formation and
importanceof ozone.
Describethe development
of chlorofluorocarbons.
Thke a moment to look aroundyou. where did all the "stuff'you seecome
from? All the stuff in the universe is made from building blocks formed in
starssuch as the onesshown in the photo on the oppositepage.And, as you
learnedin the DISCOVERY LAB, this stuff changesform.
scientists are naturally curious. They continually ask questionsabout and
seekanswersto all that they observein the universe.one of the areasin which
scientists work is the branch of sciencecalled chemistry.your introduction
to chemistry will begin with two unrelateddiscoveriesthat now form the basis
of one of the most important environmental issuesof our time.
TheOzoneLayer
You are probably aware of some of the damaging effects of ultraviolet radiation from the sun if you have ever suffered from a sunburn. overexposure
to ultraviolet radiation also is harmful to plants and animals, lowering crop
yields and disrupting food chains. Living things can exist on Earth because
ozone,a chemical in Earth's atmosphere,absorbsmost of this radiation before
it reachesEarth's surface.A chemical is any substancethat has a definite composition. ozone is a substancethat consistsof three parlicles of oxygen.
1.1 The Storiesof Two Chemicals
I
II
L/a
Figure1-l
Earth'satmosphereconsistsof
severallayers.The laYernearest
Earth is the troPosPhere.The
stratosphereis above the
tropospnere.
atmosphereconEarth's atmosphere As you can seein Figure 1-1, Earth's
the air
andcontains
sistsof layers.The lowest iayer is calledthe troposphere
webreathe.ThetroposphereiswherethecloudsshowninFigurel..2occur
andwhereairplanesny.errofEarth'sweatheroccursinthetroposphere.
is ih" luy"r abovethe troposphere.It extendsfrom about
The stratosphere
that protectsEarth
15 to 50 kilometers (km) aboveEarth's surface.The ozone
islocatedinthestratosphere.Aboutg0ZoofEafth,sozoneisspreadoutina
layer that surroundsand protectsour planet'
The troposPhereextendsto
a h e i g h to f a b o u t 1 5 k m '
, r thunC u m u l o n i m b u cs l o u d s o
d e r h e a d sp, r o d u c et h u n d e r ,
l i g h t n i n g ,a n d r a i n .
Topic G.M.B.Dobson
T o l e a r nm o r e a b o u t G . M . B .
Dobson,visit the ChemistrY
websiteat chemistrymc.com
Activity: Researchthe work
o f G . M . B .D o b s o n .M a k e a
graph of his measurements
by year.
ozone (og) is
ozone formation How does ozone enter the stratosphere?
radiation in the upper
formed when oxygen gas is exposedto ultraviolet
made of two smaller
regions of the stratosph""re.Particles of oxygen gas are
particlesinto oxygas
the
breaks
o^lyg"n particles.The energyof the radiation
ozone' Figure 1'
form
g"n"purti.t"s, which then interact with oxygen gas to
and break apart to
5 ilustrates this process.Ozone also can absorbradiation
reformoxygengas.Thus,theretendstobeabalancebetweenoxygengasan
ozonelevels in the stratosPhere.
so its presence
ozone was first identified and measuredin the late 1800s,
becauseair
has been studiedfbr a long time. It was of interestto scientists
forms over the
currents in the stratospheremove ozone around Earth. ozone
toward
then.flows
and
strongest
equator where the rais of sunlight are the
of air
flow
the
follow
the poles. Thus, ozone makes a convenient marker to
in the stratosPhere.
Inthelg20s,G.M.B.Dobsonbeganmeasuringtheamountofozoneinthe
of the stratosphere'
atmosphere.Although ozoneis formed in the higher regions
can be measuredby
most of it is stored in the lower stratosphere,where it
Dobson measinstrumentson the ground or in balloons,satellites,and rockets.
units (DU)' His
ured levels of stratosphericozone of more than 300 Dobson
measurements'
recent
with
measufementsserveis a basis for comparison
Survey was
During 1981-1983, a researchgroup from the British Antarctic
surprisingly low
monitoring the atmosphereaboveAntafctica. They measured
the Antarctic
levels of ozone, ,"uding, as low as 160 DU, especially during
measuretheir
repeated
and
spring in october. They checkedtheir instruments
of
amount
the
in
ments.In October t985, they repofted a confirmed decrease
was thinning'
ozone in the stratosphereani concludedthat the ozonelayer
Chapter 1 Introduction to Chemistry
e
s
fD
T
rD
oxYsensas
&
Figure1-3
+
Ozone
T h i sm o d e l o f t h e f o r m a t i o n o f
ozone showsthat ultraviolet
r a d i a t i o nf r o m t h e S u n c a u s e s
oxygen gas to break down into
two individualparticlesof oxyg e n .T h e s ei n d i v i d u a o
l xygen
p a r t i c l e sc o m b i n ew i t h o x y g e n
g a st o f o r m o z o n e ,w h i c h c o n sistsof three oxygen particles.
Formation of ozone
Although the thinning of the ozonelayer is often called the ozonehole, it
is not actually a hole. You can think of it as being similar to the old sock in
Figure l-4a in which the material of the heel is wearing thin. You might be
ableto seeyour skin throughthe thinning sock.So althoughthe ozoneis still
presentin the atmosphere,the protective layer is much thinner than normal.
This fact has alarmedscientistswho never expectedto find suchlow levels.
Measurementsmade from balloons,high-altitudeplanes,and satelliteshave
supportedthe measurementsmade from the ground, as the satellite map in
Figure 1-4b shows.What could be causingthe ozonehole?
Chlorofluorocarbons
The story of the secondchemical in this chapter begins in the 1920s.
Refrigerators,which usedtoxic gasessuchas ammoniaas coolants,werejust
beginningto be producedlarge scale.Becauseammoniafumes could escape
from the refrigerator and harm the membersof a household,chemistsbegan
to searchfor safercoolants.ThomasMidgley, Jr. synthesizedthe first chlorofluorocarbonsin 1928.Achlorofluorocarbon(CFC) is a chemicalthat consistsof chlorine,fluorine, and carbon.There are severaldifferent chemicals
that are classifiedas CFCs. They are all made in the laboratoryand do not
occurnaturally.CFCs are nontoxic and stable.They do not readily reactwith
other chemicals.At the time, they seemedto be ideal coolantsfor refrigerators. By 1935,the first self-containedhome air-conditioningunits and eight
million new refrigeratorsin the United StatesusedCFCs as coolants.In addition to their use as refrigerants,CFCs also
wereusedin plasticfoamsand aspropellants
in spraycans.
Figure1-4
@ r t r e t h i n n i n g h e e lo f t h i s
s o c km o d e l st h e t h i n n i n g o f t h e
o z o n e l a y e ri n t h e s t r a t o s p h e r e .
Q ffris iolored satellitemap of
stratosphericozone over
Antarcticawas taken on
S e p t e m b e r1 5 , 1 9 9 9 .T h e l o w e s t
a m o u n t o f o z o n e( l i g h t p u r p l e )
appearsover Antarctica(dark
p u r p l e ) .B l u e ,g r e e n ,o r a n g e ,
a n d y e l l o ws h o w i n c r e a s i n g
a m o u n t so f o z o n e .
1.1 The Storiesof Two Chemicals
Concentrationof CFCsin the Atmosphere
CL
o-
= 2oo
r
\J
Now think of all the refrigerators m your
neighborhood,in your city, acrossthe country, and around the world. Think of the air
conditionersin homes,schools,office buildings, and cars that also used CFCs' Add to
your mental list all of the aerosol cans and
ptastic foam cups and food containers used
eachday throughout the world' If all of these
productscontainedor were madewith CFCs,
imagine the quantitiesof thesechemicalsthat
could be releasedinto the environment rn a
single day.
I I I I I I I I I I
#
150
H
ffi
ffi
120
'u+ 'n*
z^
1o- |u"t
bon 7a
bo, la
&o"
br, b'n bo, &$
Year
Figure1-5
Quantitiesof CFCsin the atmos p h e r ec o n t i n u e dt o r i s eu n t i l a
b a n o n P r o d u c t sc o n t a i n i n g
them went into effect in manY
countries.
Scientistsfir stbegantonoti c ethepr e
in the 1970s.
enceof CFCsin theatmosphere
theamountof CFCs
Thevdecidedto measure
andfound that quantities
in the stratosphere
year afteryear'
increased
in the stratosphere
L-5' But' it
Figure
in
is shown
This increase
a threat
pose
*r, ,n""*n, that cFCs dio not
theyaresostable'
because
to theenvironment
hadbeennoticed
occuffences
Two separate
andmeasured:theprotectiveozonelayerintheatmospherewasthinning,and
increasinglylargequantitiesofusefulCFCsweredriftingintotheatmooccuffences?Before you
sphere.couro therebe a connectionbetweenthe two
someof the basic
learn the answerto this question,you need to understand
for that
scientists'
most
ideas of chemistry and know how chemists-and
matter-solve Problems'
Assessmenl
October Ozone Concentrations
r. Why is ozone important in the atmosphere?
2. Where is ozone formed and stored?
3. What are CFCs?How are theYused?
+. Thinking Critically Why do you think ozoneis
formed over the equator?What is the connection
between sunlight and ozone formation?
5. Comparing and Contrastin$ What general
trend in ozone concentrationis shown in the graph
at the right? How does the data for the years
1977-198'7on this graph compareto the same
time span on the graph in Figure L-5? What do
you notice?
450
400
3 3s0
a
9o :oo
b& bt
a
i zso
5
o
h? I
a
2oo
I
r?.
I|
150
p
I
a
100
R
50
0 L
c aE
Chapter'l Introductionto Chemistry
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