2.+solutions (1)
TRANSCRIPT
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Solutions
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Types of solutions
Solute
Solvent
SolutionPhase
Examples
Gas Gas Gas Air, natural gas
Gas Liquid Liquid Club soda (CO2 in H2O), artiial blood
(O2
in per!uorodealin)
Liquid Liquid Liquid "od#a
Solid Liquid Liquid Saline
Gas Solid Solid H2$%d
Solid Solid Solid &'#arat gold (Ag in Au)
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nergetis of solutionfor*ation
• &) %ure sol+ent separated sol+ent *oleules
– ∆H&- beause inter*oleular fores are being
bro#en
•
2) %ure solute
separated solute *oleules – ∆H2- beause inter*oleular fores are being
bro#en
• .) Separated sol+ent and solute *oleules solution
– ∆H./- beause inter*oleular fores are being
for*ed
∆Hsolution0∆H&1∆H21∆H.
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3at it *eans to be ideal
• 4or ondensed p3ases, 5e #no5 t3at t3ereare inter*oleular fores, 53i3 *ay befairly signiant6 Considering t3e ase of
7ust t5o di8erent types of *oleules in asolution (A and 9), t3ere are really three types of interations: AA, A9 and 996
• ;f t3e solution is ideal, t3en t3e
*agnitudes of t3ese interations are allequal < i6e6 it doesn=t really *atter 53oyour neig3bor is>
• ∆Hsolution 0 -,
∆"solution 0 -
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3at it *eans to be nonideal
• ;nter*oleular fores bet5een solute and sol+ent*oleules are stronger t3an ot3er inter*oleularfores
– ∆H.∆H&1∆H2
– ∆Hsolution /-, ∆"solution /-
• ;nter*oleular fores bet5een solute and sol+ent*oleules are 5ea#er t3an ot3er inter*oleularfores
– ∆H./∆H&1∆H2
– ∆Hsolution -, ∆"solution -
– ;f fores are *u3 5ea#er, t3en a solution *ay not for*at all>
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?aoult=s La5
• Consider a solution *ade up of sol+ent A(large purple sp3eres) and solute 9 (s*allgreen sp3eres)6
• T3e rate at 53i3 A lea+es t3e surfae
(+apori@ation) is proportional to 3o5 *anyyou 3a+e on t3e surfae, 53i3 is
proportional to t3e *ole fration: r0#A
• T3e rate at 53i3 A o*es ba#(ondensation) is proportional to t3eonentration of t3e gas, 53i3 is
proportional to t3e partial pressure: r0#=%A• Sine t3ese t5o rates *ust be t3e sa*e:
6
4or a pure liquid A0& so #$#=0%AB6 T3is *eans
t3at
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;deal solutions
• An ideal solution is one 53ere?aoult=s La5 is obeyed6
• Sine %0%A1%9, and t3e +apor
pressure for a liquid is t3esa*e as t3at for a gas, for anideal solution 5e an say t3at
• 4urt3er*ore, sine A190&,
or
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a*ple of an ideal solution
• Solutions tend to be3a+eideally 53en t3e sol+ent (A)
and solute (9) are si*ilarDto ea3 ot3er in ter*s of*oleular struture, polarity,inter*oleular fores, et6
• 6 9en@ene and toluene(*et3ylben@ene)
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a*ple of a nonidealsolution
• Signiant de+iations fro*?aoult=s La5 (eept for
dilute solutions)• Typially ta#es plae 53en
solute and sol+ent aredissi*ilar
• 6 Carbon disulde (CS2)
and aetone (2propanone)
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Co*parison of solutionbe3a+ior
• Fotie t3at in t3e li*it of+ery +ery onentrated
solutions of 9, real solutionsapproa3 ?aoult=s La56
• 4or dilute solutions of 9, t3ereal solution 5ill also
approa3 Henry=s La56
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a*ple
• T3e +apor pressure of pure 5ater at2-6- oC is &6 **Hg6 3at is t3e+apor pressure at 2-6- oC abo+e a
solution t3at 3as -62- *ol C&2H22O&&
(surose) and 6- g CO(FH2)2 (urea)
dissol+ed per #ilogra* of 5aterI
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Solution
• 4irst nd t3e *oles of urea: n 0 6-g $ J-6-J g$*ol 0 &62 *ol urea
• Fet nd t3e *oles of 5ater: n 0&--- g $ &K6-2 g$*ol 0 6 *ol5ater
• Fo5 deter*ine t3e *ole fration of
5ater:
• 4inally, use ?aoult=s la5 to alulatet3e +apor pressure of t3e 5ater
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a*ple
• T3e +apor pressures of ea3 o*ponent in a *iture ofpropanone (aetone, A) and tri3loro*et3ane (3lorofor*,C) 5ere *easured at .oC 5it3 t3e follo5ing results:
• Conr* t3at t3e *iture onfor*s to ?aoult=s La5 for t3e
o*ponent in large eess and to Henry=s La5 for t3e*inor o*ponent6 4ind t3e Henry=s La5 onstants6
xC 0 0.20 0.40 0.60 0.80 1
%C (torr) - .6. K26 &'2 2-- 2.
%A
(torr) .' 2- & 26. .J6K -
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Solution
• ;t is usually a good idea to plot t3edata rst6
• 4or ?aoult=s la5, 5e need to loo# at
t3e t5o etre*es (C
- and C
&)64or bot3 substanes (A and C) itappears t3at t3e data approa3 t3eirorreponding li*its (%AB and %CB)
• 4or Henry=s la5, 5e need to loo# at
t3e sa*e li*its and t to a straig3tline6 4or A, 5e need t3e slope asC&, 53i3 is approi*ately 2.6.
#%a6 4or C, 5e need t3e slope asC-, 53i3 is approi*ately 226-
#%a6
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%ressureo*positiondiagra*s
• e 3a+e already seen 3o5 todeal 5it3 binary *itures6
•
;f 5e assu*e an idealsolution, t3en t3e +aporpressure of ea3 o*ponent5ill be gi+en by ?aoult=s la5:
• T3us t3e total pressure 5illbe: or
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%ressureo*positiondiagra*s
• 3at about t3e +aporI T3e *ore+olatile o*ponent (3ig3er "%)s3ould be present in greaterquantities in t3e gas p3ase6
• Msing Nalton=s la5,
• Sine t3e total pressure *ust bet3e sa*e as t3e +apor pressure (atequilibriu*), for an ideal solution5e an say t3at:
– Fotie t3at if %AB$%9B&, t3en yAA
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%ressureo*positiondiagra*s
• e an also rearrange t3eseequations to sol+e for t3e total
pressure (%A1%9) as a funtionof t3e o*position in t3e gasp3ase (rat3er t3an t3e liquidp3ase):
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4ree@ing point depression and
boiling point ele+ation
• Consider solutions 53ereonly t3e sol+ent is +olatile,and t3e solute onlydissol+es in t3e liquidp3ase of t3e sol+ent
• ∆ Tf 0 iE f m
• ∆ Tb 0 iE bm
i 0 +an=t Ho8 fator (i 0 & fora noneletrolyte, & for a
5ea# eletrolyte, or P ofpartiles for a strongeletrolyte)
E f 0 free@ingpoint
depression (ryosopi)
onstantE b 0 boilingpoint ele+ation
(ebulliosopi) onstant
m 0 *olality
3ttps:$$5556boundless6o*$3e*istry$solutions$olligati+epropertiesnoneletrolytesolutions$free@ingpointdepression$
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a*ple
• 3at is t3e free@ing point of anaqueous surose solution t3at 3as26- g C&2H22O&& per &--6- g H2OI
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Solution
• 4irst nd t3e nu*ber of *oles of surose: n0 26- g $ .'26. g$*ol 0 -6-.- *ol surose
• Fet nd t3e *olality of t3e solution: m 0
-6-.- *ol $ -6&--- #g H2O 0 -6.- m• Fet deter*ine t3e 3ange in free@ing point:∆ Tf 0 iE f m 0 &(&6KJ oC$m)(-6.- m) 0
&6.J oC
• Sine t3e nor*al free@ing point of 5ater is -oC, t3e ne5 free@ing point 5ill be (-1 &6.J)oC, or &6.J oC
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Os*oti pressure
• Os*osis net !o5 of sol+ent*oleules t3roug3 ase*iper*eable *e*brane – Sol+ent *oleules go fro* a
solution of lo5er onentrationto a solution of 3ig3eronentration (solute is notable to pass t3roug3)
• Os*oti pressure (Π) 0
pressure required to stopos*osis
• Π 0 Q?T, 53ere Q 0 *olarity
3ttp:$$3e*istry6tutor+ista6o*$p3ysial3e*istry$os*otipressure63t*l
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a*ple
• An aqueous solution is prepared bydissol+ing &6- g of 3e*oyanin, aprotein obtained fro* rabs, in -62-
L of 5ater6 T3e solution 3as anos*oti pressure of -6--.'2 at* at2E6
• A) 3at is t3e *olar *ass of3e*oyaninI
• 9) 3at s3ould t3e free@ing point of
t3e solution beI
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Solution (part a)
• Msing t3e os*oti pressure, 5e annd t3e *olarity of t3e solution:π0Q?T so Q0π$?T
• Fet nd t3e *oles of 3e*oyanin:Q0n$" so n0Q"
• 4inally, nd t3e *olar *ass:n0*$QQ so QQ 0 *$n (QQ 0 *olar*ass)
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letrolyti solutions
• Feed to ta#e into aount t3e total iononentration
– 4or strong (dilute solutions of) eletrolytes you anuse stoi3io*etry
– 4or 5ea# eletrolytes you an use equilibriu*(o*ing soon>)
• +an=t Ho8 fator (i) < orretion for olligati+eproperties of eletrolytes
∆ Tf 0 iE f m
∆ Tb 0 iE bm
Π 0 iQ?T