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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