ComparingRatesof
Evaporation
1! everal factors determine how fast a sample of liquid will evaporate.
volume of the sarnplels a key factor. A drop of water takes tess
Drfr*
time to evaporate than a liter of water. The amount of energy supptied
to the sampleis another factor.ln this lab, you will investigatehow the
type of liquid and temperature affect the rate of evaporation.
Problem
How do intermolecular
forcesaffect the evaporation ratesof liquids?
Objectives
. Measureand romparethe
ratesof evaporationfor
differentliquids.
r class'fyliquidsbasedon
their ratesof evaporation.
r Fredictwhich intermolecular forcesexistbetween
the particlesof each
liquid.
Materials
distilledwater
ethanol
isopropylalcohol
acetone
household
ammonia
droppers(5)
smallplasticcups(5)
greasepencilor
maskingtape and
a markingpen
paper towel
squareof waxed
pap€r
stopwatch
Safety Precautions
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Always wear safety gogglesand a lab apron.
Wear glovesbecausesorneof the liquidscan dry out your skin.
Avoid inhalingany of the vapors,especiallyammonia.
Thereshould be no open flamesin the lab; someof the liquids are
flammable.
Pre-Lab
l. I{eatl the entire CHEIIILAB. U.r^efhe data tahle
on the next page.
.\
;i,)
z,rfuh;t is evuporation'Jlfqscribc rvhat happens If
the rnolscruIarlevel during evayroration.
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6
'Lr
l, I-ist thethreepossibleintennnleculiulorces.Wrich
Which fbrceis the strongest?
tbrceis the u,eakest'l
u{earf?,
t ;
ffr"nq€r*:
a
'r
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4. Luok at the materials list for this lah. Consider the
liquicl.syou rvill test. Precliutu,hich liquids
.fr!
rvill evaporatequickly and which unill take longer
t(] evap()rate.
fas*"e"r*;/:-
50
Chem is t r yM
: a tte r a n d C h a n g e ' C h a p te r1 3
T"h
t
f:t
Procedure
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Usc a gr:easepencil or tnasking taFe to lahel each
of five srnall plastic cups. Use A firr distilled
rvater, B for ethanol. C tirr isupnrpyl aluohol, D
lor acetune. and E fulr householtl atntnutria.
2. Place tlre plastlc cupriorl a papcr towel.
drops rnust be as tar apilrt iis pr:ssihle to
avoid rnixing.
5. I]avcryour-stop\\riltchrcady. Collcct riorile water
in ,vour wiiter dropper and place a single drop on
the u,axed paper:.13cgintinring. Time holv long it
takes firr the drop to com;rletely evaporate.While
you rvait. make two drarvings of the drop. One
clrawing should shor,vthe shape of the drop as
vierved Irorn above. The other clrarvir
a side view at eye level
e.lrop takes longer
:t. use a dnr;lper fu c:ollectabout I mL uf distilled
rvater ancl ;:lace the rvater in the cup lahcled .4.
Place the r:lnrppcrrxr the pa; er towel directly in
fl'qrntol the cup. Repert r,r,iththe other liquids.
.srt/
diita table.
tL. Place a squars of wa.ted paper on your lnb sur-
6. Repeat step 5 with the tbur other liqr.ricls. r
firr-:e.Illan r,vl"tere
on fhe waxetl paper you rvill
place each ot thc 5 dnrps that you rvill test. "fhe
Wrrrate , record> 300 in your
r\
7. Use the ahove procedure to design an experiment
in lvhich you can obse,rvethe eJleut uf temperature on the r:atetrJ'evapnratinnof ethanol. Your
'teachcr will provide a siunple ol""varm ethanol.
Rccord yntrr ohserr,ations.
Cleanupand Disposal
1. Cnrn-rpleLrptlre rvaxed paper and place it in the
containcrassignedby yuur teac'her.
t. Placeunusedlicluidsin the containersspecitied
by your teacher.
3. \\'irsh oui all dr:nppersaneltest tubes except those
used for distilled u'ater.
Distiiledwater
Ethanol
Ethanol{warm)
lsopropylalcohol
Flou se holdam m onia
Questions:
1. Rank the evaporation rate of the liquids, from fastest to slowest.
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Fast -----------------------------------------------------------------------------------------------> Slow
2. Based on your data, in which liquid(s) are the attractive forces between the molecules likely to be…
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Hydrogen bonding:! !
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3. Make a generalization about the shape of a liquid drop and the evaporation rate of the liquid.
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4. What is the relationship between surface tension and the shape of a liquid drop?
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Which intermolecular force increases surface tension?!
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5. The isopropyl alcohol used in this investigation (“rubbing alcohol”) contains 5% water. Would
pure isopropyl alcohol evaporate more quickly or more slowly? Give a reason for your answer.
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6. The “household” ammonia used in this investigation is a mixture of ammonia and water. Pure
ammonia is a gas at room temperature. Based on your data, is there more ammonia or water in
household ammonia? Give a reason for your answer.
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7. How does the rate of evaporation of warm ethanol compare to ethanol at room temperature?
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Use kinetic-molecular theory to explain your answer.
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