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THERHODYN,V.liCS OF A�UEOUS .Al·IDW
ACID SOLUTIONS
A thesis presented in partial fulfilment
of the requirements for the degree of
Doctor of Philosophy in Chemistry
at �assey University
Rex Stuart Humphrey
1977
ABSTRACT
1. The vapour pressures of L-serine-water solutions have been
measured at 288.15K and 298.15K using a differential static
method. From these the activity coefficients for L-serine as
a function of concentration at each temperature have been
calculated.
2. The integral enthalpies of finite dilution of aqueous solutions
of L-alanine, L-arginine, L-cysteine, glycine, L-serine and
L-valine ha�e been measured at 298.15K using an LKB 10700-1 flow
microcalorimeter. These have been used to calculate the relative
apparent molal enthalpies and the relative partial molal enthalpies
of the particular solutes as a function of concentration.
3. The relative partial molal entropies of water in aqueous solutions
of the amino acids L-alanine, glycine, L-serine and L-valine have
been calculated from activity data and from enthalpy of dilution
data.
4. The results have been discussed qualitatively in terms of the
proposals of Frank and Evans for water-solute interactions.
ACK.NO\v'LEDG:2l ENTS
I would like t o thank Professor G . N . t-lalcolm and Dr I . D . i-/atson
for their supervision of this thesis.
For many helpful suggest ions I v1ould like t o t hank Dr G.R.
Hedwig. J\lso I would especially t hank Dr I .R. �;cKinnon for his t imely
encouragemen t and many useful discussions.
I would like t o express my appreciat ion t o t he t echnical staf f
for their assist ance and in part icular, �.essrs H. Grant, S. C oat es ,
N. l<,oot and !· •• 'iilne whose cheerful assist ance was invaluable in
development and const ruct ion of t he vapour pressure apparat us.
For f inancial assist ance I acknowledge the awards o f a
Post graduate Scholarship and a Shirtclif fe Fellowship from t he
University Grant s Commi t t ee and also a Depart ment al Demonst rat orship
f r om Massey Universit y.
Finally, I would like to thank my wife , Anne , for her patient
support and encouragement during this thesis.
CHAPI'ER I
CH/PI'� II
'l'ABLE OF CON'l'ENTS
INTRODUCTION
I . A IHTRODUCTIOf�
I .B T!IEHl·,ODYl'lr(·.ICv OF AhiNO ACID SOLUTIOi·lS
I.B1 Ide�l So lut ions
I.B2 Real Solutions
I.B3 Act ivity Coef ficient s from Vapo ur Pressures
1
11
11
11
12
I . B4 \ct iv it y Coe ff ic ient s o f the S o lut e 16
I . B5 Enthalpies of Solut i o ns 17
I .B6 Te mper�t ure De pende nc e o f the Ac t i vit y 20 Coe f f ic ient
I . B7 Ent ropie s of Di lut ion of Amino Ac id 21 Solut ions
li. A Dl:.:I'L:I<L Ii I AT IOtl OF ACT I'! IT I.C::S OF fU''t II'lO ACIDS
IN i�ATER
II. 1 he thods o f Det e rmining Ac t ivit ie s
II .A2 Vapour Press ure Apparat us
II.A3 Vapour Spac e Vo lume o f the Apparat us
I I . i\4 S ample Pre pann:ion
I I . A5 Vapour Pressure he asure ments
I I .B ENTHALPY OF DILUTION F.EASUREHENTS
II .B1 Calori me t e rs f o r Enthalpy o f Dilut i o n Heasure ment s
I I .B2 Calori me t e r
I I . B3 Sample Pre parat i on
I I . B4 Enthalpy o f Di lut i on Measurement s
I I . C DENSITIES OF AQUEOUS Al'i INO ACID SOLUTIONS
I I . C1 Experiment al
I I . C2 Calc ulat ion o f Dens i t i e s
23
23
29
39
42
45
45
50
51
53
56
56
56
C HAPrER I I I
CHAPI'ER IV
CHAPI'ER V
EXPERI I'iENT AL RESUL'l'S
Ill . A VAPOUR PRESSURE t·iEASUR.iJ'IENTS
III.A1 Vapour Pressures o f Pure \-lat e r at 5<3 288.15K, 293.15K and 298.15K
I I I . A2 Vapo ur Pre ssures o f L-Serine -Wat er 58 Solu t i o ns at 2d8.15K and 29B.15K
III .B :t:I�THALPY OF DILUT IOIJ ,£J\3URB-iENT.S 59
I I I .B1 Int e gral llit halpi e s of Di lut i o n of 59 Aque o us �i no Ac i d S olut i o ns at 298.15K
ANALYS IS OF RESULTS
IV . A
IV.B
IV . C
ANALYSIS OF VAPOUH Pl�ESSUHE hEASUREHEHTS 60
IV. A1 Ac t i vi t y Coe ffi c i e nt s of L-Serine - 60 Wat er S o lut i o ns at 288.15K and 29B.15K
IV.A2 Compar i s o n wi t h Literat ure Values 61
IV •. t3 Error Analysis 62
ANALYS I S OF I;'IT�Gi:.�L EN'l'HALPIES OF DILU'riOii 63
I V.B1 Re lat i v e 1ppare nt Molal Enthalpie s at 63 298.15K
IV.B2 R e lat i ve Par t i al Ho lal Enthalpie s at 63 29B.15K
IV .B3 Comparison with Lit erat ure Values 61+
IV .B4 Error Analy s i s 64
THlPEHATURE DEPENDEN CE OF /tCT IVITY
COEFFICIEN TS OF L-SEIUNE-ivATER SOLUT IONS
IV . D ENTROPI ES OF DILUTION 66
DIS CUSSION 67
B IBLIOGHAPHY 72
LIST OF ?IGUR!::S
Figure
1.1 Frank i.illd \Jen Ionic Sol ut ion �·.odcl
I.2 Some Amino Acid Structures
II.1 Vapour Pressure ,�pparatus
II.2 Differential Lnt;nifyinc L .. mo:�eter
II.3 V01.pour Pressure .11.ppnratm;: Voluce of tite Vnpour Space
II.4 De�assing Apparatus
II.5 Vnpour Pressure kpparatus
II.o Hydrostat ic Pressures in Vapour Pressure ,\pparatus
II. 7 Calorimeter
n.8 Typical-Hecorder Trace for a Dilution Experiment
Ill.1 E..xperimento.l Vapour Pressures of L-Serine-\-/ater Solutions
IV .1 liOle FrL:tction H< . .1.tio x1;x2 vs lot; �1 for L-Serine-V/ater Solutions
IV.2
lV.3
IV .4
IV.5
IV .6
IV.?
l·;ole J<'raction H01.tio x2/x1 vs log o 2 for L-Serine-1'/ater Solutions
Relative Apparent holal Enthalpies of 1'-.mino Acids in 'dater
Relative Partial 1-iolal Enthalpies of Amino Acids in '.Vater
�elati ve 1'.pparent l·!olal Enthalpy of Glycine in \vat er: a comparison with literature
Relative Apparent 1-iolal Enthalpy of L-Alanine in 'dater: a comparison vli th literature
Relative Apparent Holal Enthalpy of L-Valine in Water: a comparison with literature
V.1 Some Amino Acid Structures
V.2 Relative Apparent Molal Enthalpies of 1\.mino Acids in \o/ater
V.3 Relative Partial Molal Enthalpies of Amino Acids in Water
V .4 Relative Partial �olal Entropies of \-later in Aqueous Amino Acid Solutions