The equilibrium of silver chloride, silver hydroxide, potassium hydroxide, and potassium chloride in
aqueous solution at different temperatures and varying concentrations of potassium hydroxide : the
calculation of the heat of the reaction
by William Wallace Harrity
A THESIS Submitted to the Graduate Committee in partial fulfillment of the requirements for the
Degree of Master of Science in Chemistry
Montana State University
© Copyright by William Wallace Harrity (1933)
Abstract:
I. The reaction AgCl + KCH = KCl + AgOH was carried out at 30°, 40° and 50° using different
concentrations of aqueous potassium hydroxide and the equilibrium constants were obtained.
2. It was found that the concentration of potassium hydroxide used had little if any effeot on the
equilibrium of the reaction.
3. The heat of the reaction at the various temperatures was calculated by use of van't Hoff's reaction
isochore equation.
4. The heat of the reaction was found to decrease quite rapidly as the temperature was increased.
5. Conparisons are given with data submitted by Newton,3 and the heat of the reaction calculated by
use of the above mentioned data.
6. Data will have to be secured for the activities of ions in solutions of higher concentration before the
true equilibrium constants for these solutions can be determined.
The author wishes to take this space to express his appreciation to Dr. R. M. Melaven, Dr; O. E.
Sheppard, Dr. B. L. Johnson, and Professor P. C. Gaines of the chemistry department, and Mr. Jesse
Green, of the Montana State College Agricultural Experiment Station for the time, assistance, and
inspiration they have given him during the year while the above work was being carried to completion. THE EQUILIBRim OF SILVER CHLORIDEi.
SILVER HYDROXIDE, POTASSIUM HYDROXIDE, AM) POTASSIUM
CHLORIDE IN AQUEOUS SOLUTION AT DIFFERENT TEMPERATURES
AND VARYING- CONCENTRATIONS OF POTASSIUM HYDROXIDE*
THE CALCULATION OF THE HEAT OF THE'REACTION.
BY
WILLIAM WALLACE HARRITY.
' A THESIS
S u b m itted to th e G raduate Committee in
p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts
f o r th e Degree of, M a ste r o f S cience
i n C hem istry a t Montana
S ta te C o lleg e
' I n Charge "of M ajor Worl
. Chairman E x a m in in g ^ C # m ittee
/Chairm an G raduate Committee
Bozeman,. Montana
’,i; ID'I K M R * '
I''I/W . I vIi-lI
N"57#
H T #
2
TABLS OF OONTtiNTS
Page
3
I n tr o d u c tio n
5
t P r e p a r a tio n o f m a te r ia ls
P rocedure
11
T ables o f d a ta
14
Data f o r com parison
17
D isc u ssio n o f r e s u l t s
18
C a lc u la tio n o f th e e q u ilib riu m c o n s ta n t
18
The h e a t o f th e r e a c tio n
21
Summary
27
L i te r a tu r e c i t e d
28
ILLUSTRATIONS
T herm ostat ( f ig u r e I)
8
S haker o r a g i t a t o r ( fig u r e 2)
9
R ea c tio n a p p a ra tu s ( f ig u r e 3)
10
44561
5
IHE EQUILIBRIUM OF SILVER CHLORIDE, POTASSIUM HYDROXIDE,
SILVER HYDROXIDE, AHD POTASSIUM CHLORIDE IN AQUEOUS SOLUTION AT DIFFERENT
TEMPERATURES AND VARYING CONCENTRATIONS OF POTASSIUM HYDROXIDE.
THE CALCULATION OF THE HEAT' OF THE REACTION.
INTRODUCTION
G. W etzlar in 1888,' and J . P e rc y ? ' i n 1880, found t h a t a t o rd in a ry
te m p e ra tu re s an aqueous s o lu tio n o f sodium o r p o tassiu m c h lo r id e would r e a c t
vfith m o ist s i l v e r o x id e to g iv e a w h ite p r e c i p i t a t e o f s i l v e r c h lo rid e and a
s o lu tio n o f th e a l k a l i h y d ro x id e . The a c ti o n , however, was n o t com plete, and
i f th e s o lu tio n was b o ile d th e r e v e rs e a c tio n to o k p la c e p ro d u cin g s i l v e r ox"
id e . T h is was found to be tr u e o f a l l . th e ,a lk a lin e e a r th c h lo r id e s .
W. G regory i n 1859, and E . Mohh6 'i n 1848, made s i l v e r oxide by b o il*
in g f r e s h l y p r e c i p i t a t e d s i l v e r c h lo rid e w ith a s o lu tio n o f aqueous p o ta ssiu m
h y d ro x id e . The s i l v e r oxide" th u s, made was washed w ith w a te r to remove th e a lk ­
a l i and d r ie d on f i l t e r p a p e r.
In 1908, "Noyes and Kohni p u b lis h e d a p ap er on th e measurement o f th e
e q u ilib riu m betw een s i l v e r o x id e , s i l v e r c h lo r id e , p o ta ssiu m h y d ro x id e, p o t*
assium c h lo r id e , and w a te r. They found th e v a lu e o f th e e q u ilib riu m c o n s ta n t
a t 85° to be 0.00937* Noyes a n d 'E o h r' s r e s u l t s were n o t v e ry c o n s is te n t and
i n 1988, Newton^-, w orking a t Purdue U n iv e r s ity , p u b lis h e d a p a p er on "The
E q u ilib riu m o f S ilv e r Oxide and S ilv e r C h lo rid e w ith Aqueous P otassium C hlor#
id e and P o ta ssiu m H y d ro x id e ,n The method u sed by Newton w a s ,to p la c e v a ry in g •
p ro p o r tio n s o f s i l v e r o x id e and s i l v e r c h lo r id e in g ro u n d -g la s s -s to p p e re d
P y rex E rlenm eyer f l a s k s , and add th e d e s ir e d q u a n t i t i e s o f p o tassiu m hydrox—
4
id e , p o ta ssiu m c h lo r id e » and w ater and r o t a t e th e sam ples "in a th e rm o s ta t a t
25° i 0 .0 2 ° f o r p e rio d s o f tim e v a ry in g from s e v e r a l h o u rs to th r e e days.
The e q u ilib riu m was .approached from b o th s i d e s i K o c o n s is te n t d if f e r e n c e s were
o b se rv e d . Samples o f th e l i q u i d p o rtio n s -w e re th e n f i l t e r e d from th e f l a s k s
and t i t r a t e d w ith 0 .5 N s u lp h u ric a c id , u s in g p h e n o lp h th a le in a s an in d i c a t ­
o r . The s o lu tio n was th e n c a r e f u l ly e v a p o ra te d to sm all b u lk and t i t r a t e d
e le c tr o m e tr ic a lly w ith 0 .0 1 H s i l v e r s u l f a t e s o lu tio n , u s in g a s i l v e r - s i l ­
v e r c h lo r id e e le c tr o d e and c o n n e c tin g to a s a tu r a te d p o ta ssiu m s u l f a t e m ercurous su lfa tei-m e rcu ry e le c tro d e * The sam ples o f s i l v e r o x id e were p re ­
p a re d i n d i f f e r e n t ways b u t th e v a lu e s o b ta in e d d id n o t d i f f e r s i g n i f i c a n t ­
l y from one a n o th e r. The av erag e v a lu e o f th e e q u ilib riu m c o n s ta n t u s in g an
a p p ro x im a te ly 0 .1 H s o lu tio n o f p o tassiu m h y d ro x id e a t 25° ± 0 .0 2 ° was
found to be 0 .00905.
The r e s u l t s o f N ew ton's experim ent g iv e v a lu e s somev/hat below
th o s e o b ta in e d by Noyes and Kohr, b u t i n a l l p r o b a b ility th e y ag ree w ith in
th e l i m i t s o f e x p e rim e n ta l e r r o r . The e q u ilib riu m c o n s ta n t f o r 0 .05 N and
0 .1 N s o lu tio n s a p p e a rs to be th e same w ith in e x p erim en tal e r r o r .
The purpose o f t h i s p ap er i s :
(I ) to d eterm ine th e e q u ilib riu m
c o n s ta n t f o r th e r e a c tio n
AgOl + KOH s
AgOH 4 KCl
i n aqueous s o lu tio n a t d i f f e r e n t te m p e ra tu re s and v a ry in g c o n c e n tra tio n s o f
p o ta ssiu m h y d ro x id e , and (2) to d eterm ine by c a lc u la tio n th e h e a t o f th e
re a c tio n *
EREPARATIOH OF MATERIALS
'
5
"
The g r e a te s t d i f f i c u l t y e n co u n te re d in p re p a rin g m a te r ia ls was in
th e p r e p a r a tio n o f c a r b o n a te -fr e e p o ta ssiu m h y d ro x id e. The g e n e ra l method
u sed was to e le c tr o l y z e an aqueous s o lu tio n o f a p o tassiu m s a l t u s in g a mer­
cu ry cath o d e and a p la tin u m anode. By t h i s method th e p o ta ssiu m amalgam was .
• made. Then by r e v e r s in g th e c u r r e n t th e amalgam was broken down and th e p o t­
assium h y d ro x id e o b ta in e d .
- An a tte m p t was f i r s t made to p re p a re th e p o ta ssiu m h y droxide by
e le c tr o l y z in g a s a tu r a te d s o lu tio n o f p o ta ssiu m o x a la te . The s a tu r a te d s o l­
u tio n of p o ta ssiu m o x a la te was p la c e d i n an e l e c t r o l y t i c c e l l and m ercury
p la c e d i n th e bottom o f th e c e l l . A p la tin u m anode"was suspended i n th e
s o lu tio n and a n o th e r p la tin u m -w ire s e a le d i n a g la s s tu b e was p la c e d in
c o n ta c t w ith th e m ercury. E l e c t r o l y s i s a t 8 .5 to 8 .7 am peres and 4 .5 to 5
v o l t s was c a r r i e d on f o r f i v e h o u rs . The s o lu tio n was th e n removed from
th e to p o f th e m ercury and th e amalgam was washed w ith c o ld d i s t i l l e d w a ter
u n t i l i t gave no tr a c e o f o x a la te when te s te d , w ith one drop o f a 0 .0 1 H
p o ta ssiu m perm anganate s o lu tio n . The washed amalgam wa§ th e n p la c e d in a
d e s ic c a to r in to which c a rb o n d io x id e ^ fre e a i r was p a sse d and covered w ith
d i s t i l l e d w a te r. The c u r r e n t was re v e rs e d u s in g a p la tin u m w ire suspended in
th e s o lu tio n a s th e cath o d e and a n o th e r p la tin u m w ire co n n ected to th e am al­
gam a s an anode.
The c u r r e n t u sed w as.0 .1 0 to 0.15 am peres and th e v o lta g e
was 1 .0 to 1 .8 v o l t s . When th e hy d ro x id e had been formed t e s t s were made f o r
th e p re se n c e o f "m ercuric, m ercurous, c a rb o n a te , and o x a la te io n s .,T h e f i r s t
th r e e w ere found to be a b s e n t b u t th e o x a la te io n was p re s e n t in s u f f i c i e n t
q u p $ i t j r to re d u c e fo u r to f i v e drops o f a 0 .0 1 H p o tassiu m perm anganate
s o lu tio n . T h is method had to be d is c a rd e d a s u n s a t i s f a c t o r y .
=. .
..
.
.
?
6
The same g e n e r a l method was th e n u sed w ith a s a tu r a te d s o lu tio n o f
h ig h g rade p o ta ssiu m h y d ro x id e . The y i e l d o f amalgam in t h i s case was to o
s m a ll to p e rm it i t s use*
F i n a l l y i t was found t h a t by u s in g a s a tu r a te d s o lu tio n o f 0. P .
p o ta ssiu m c h lo r id e a v e ry s a t i s f a c t o r y amalgam co u ld be p re p a re d and th e
p o ta ssiu m hydro x id e o b ta in e d was f r e e from c h lo r id e , c a rb o n a te , m ercurous
and m ercu ric io n s ; A s a tu r a te d s o lu tio n o f G. P . p o ta ssiu m c h lo r id e was
e le c tr o ly z e d u s in g a p la tin u m anode a n d -a m ercury c a th o d e . The le a d w ire to
th e m ercury was s e a le d in a g la s s tu b e to p re v e n t c o n ta c t w ith th e s o lu tio n .
The anode was a f l a t s p i r a l o f p la tin u m which was p a r a l l e l to th e s u rfa c e o f
th e m ercury and submerged i n th e s o lu tio n to a dep th o f 8 .5 to 3 .0 c e n t i m e te rs . The e l e c t r o l y s i s was c a r r ie d on f o r 4 to 5 h o u rs a t 8 am peres and
4 .5 v o l t s . The amalgam was removed from t h e " c e l l and washed w ith c o ld d is ­
t i l l e d w a ter u n t i l i t gave no tr a c e o f c h lo rid e io n s on t e s t i n g i t w ith s i l “
v e r n i t r a t e i n a n i t r i c a c id s o lu tio n . When th e amalgam was washed w ith c o ld
d i s t i l l e d w a te r v e ry l i t t l e decom p o sitio n to o k p la c e , b u t.w ith warm d i s t i l l ­
ed w a te r c o n s id e ra b le hydrogen was e v o lv ed . The washed amalgam was th e n
p la c e d i n a d e s ic c a to r in to which carb o n d io x id e - f r e e a i r was p a sse d and was
co v ered w ith d i s t i l l e d w a te r. A p la tin u m cath o d e was suspended in th e s o l­
u ti o n and a n o th e r p la tin u m w ire s e a le d i n a g la s s tu b e was co n n ected w ith
th e amalgam. D uring th e p ro c e s s o f b re a k in g down th e amalgam to form th e
p o ta ssiu m h y d ro x id e th e c u r r e n t u sed was 0 .1 0 to 0 .1 5 am peres and 1 .8 to 1 .5
v o l t s ; The low c u r r e n t was u sed to p re v e n t a s much a s p o s s ib le th e fo rm a tio n
o f m ercurous o x id e . The p o ta ssiu m h y d ro x id e p re p a re d i n t h i s manner was ap­
p ro x im a te ly 1 .5 M and i t was d i l u t e d w ith d i s t i l l e d w a ter to o b ta in th e re»»
q u ire d s o lu tio n s . The p o ta ssiu m h y d ro x id e s o lu tio n s were s to r e d in waxed
7
b o t t l e s and k e p t f r e e o f c a rb o n a te by means, o f soda lim e tubes*
The s i l v e r c h lo rid e was made by th o ro u g h ly m ixing an ap p ro x im ately
0 .1 H s i l v e r n i t r a t e s o lu tio n w ith an a p p ro x im a te ly 6 N h y d ro c h lo ric a c id
s o lu tio n . The p r e c i p i t a t e d s i l v e r c h lo rid e was s t i r r e d and washed w ith hotd i s t i l l e d w a te ri The re s id u e was f i l t e r e d o f f by means o f a f i l t e r pump and
s u c tio n f l a s k . The p a r t i a l l y d r ie d s i l v e r c h lo rid e was th e n p la c e d i n a
d ry in g oven h e ld a t a te m p e ra tu re o f 120° f o r s i x h o u rs . The s i l v e r c h lo r­
id e th u s o b ta in e d was f i n e l y d iv id e d and showed no re d u c tio n to f r e e s ilv e r #
The s i l v e r c h lo r id e was s to r e d i n a d ark p la c e u n t i l re a d y f o r u s e . In no
c a se was s i l v e r c h lo r id e u sed which had sto o d in th e d ark:room f o r more
th a n th r e e d a y s.
A th e rm o s ta t was c o n s tr u c te d and in s u la te d by p a ck in g e x c e ls io r
around i t . The te m p e ra tu re was c o n tr o lle d by means o f a m e rc u ry -to lu e n e
th e rm o -re g u la to r and a 500 w a tt k n ife h e a t e r . A c o n s t a n t " s t i r r i n g k e p t th e
te m p e ra tu re th e same th ro u g h o u t th e a p p a r a tu s . F ig u re 1» shows th e r e l a t i v e
p o s itio n s o f th e h e a te r , th e th e rm o -r e g u la to ri th e sh ak e r, th e s t i r r e r , and
th e r e a c tio n a p p a r a tu s .
To in s u r e th o ro u g h m ixing th e shaker* shown i n fig u r'e , 2, was em­
p lo y ed and k e p t th e r e a c tin g m ix tu re in c o n s ta n t m o tio n . The sh ak er was
f a s te n e d to th e bottom o f th e th e rm o s ta t by means' o f a h in g e and th e b o t­
tom o f th e u p r ig h t was c u t a t an an g le to a llo w th e backw ard and forw ard
m o tio n to ta k e p la c e . A s t r i p o f wood was co n n ected to th e to p o f th e up­
r i g h t and th e n fa s te n e d to a p u lle y i n such a manner t h a t th e u p rig h t was
shaken back and f o r t h a s th e p u lle y re v o lv e d . The p u lle y was co nnected d i ­
r e c t l y to a low speed m o to r.
THERMOSTAT
S h o w in g : S h a k e r (A), H e o f e r (BI, S f i r r e r C d j f i e y u / a f o r (D), a n o / / } p p a r o k u s ( € ) .
Fi9 Z
ShoKzr or A g / f Qf o r
/9 $ . 2
£
O
Reaction Apparatus
F ig 3 .
11
The r e a c tio n a p p a ra tu s , f ig u r e 3, was d e sig n e d to f a c i l i t a t e th e
f i l t e r i n g o f f o f th e l i q u i d p o r tio n s o f th e r e a c tio n m ix tu re w ith o u t making
i t n e c e s s a ry to remove th e a p p a ra tu s from th e therm ostat® The r e a c tio n cham*.
h e r, A, was a 200 c c , round bottom P y rex f l a s k , th e c o n ta in e r , D, f o r th e
wash w a te r, was a 60 c c . P y rex f lo r e n e e f l a s k , and th e f i l t e r f la s k , Bi was
a 125 c c . P y rex round bottom f l a s k . The m ethod o f o p e ra tio n w i l l be d e s c rib ­
ed under th e p ro c e d u re ;
PROCEDURE
T w en ty -fiv e c u b ic c e n tim e te rs o f aqueous p o ta ssiu m hydroxide o f
known c o n c e n tra tio n were p la c e d in r e a c tio n chamber A, f ig u r e 3, and an
amount o f s i l v e r c h lo r id e w hich was in e x c e ss o f th e t h e o r e t i c a l amount
n e c e s s a ry f o r com plete r e a c t i o n was a d d e d ./F la s k D was f i l l e d w ith d i s t i l l ­
ed w ater and th e whole a p p a ra tu s was shaken' in a th e rm o s ta t a t a c o n sta n t
te m p e ra tu re f o r a p e rio d o f tim e v a ry in g from th r e e and. o n e -h a lf to tw elve
h o u rs . E q u ilib riu m was assumed to have been e s ta b lis h e d when th e r e s u l t s o f
th r e e o r more ru n s , ta k e n over tim e i n t e r v a l s v a ry in g enough to allo w f o r
f u r t h e r r e a c t i o n , showed no v a r i a t i o n in th e e q u ilib riu m c o n s ta n t th a t
c o u ld n o t be acco u n ted f o r on th e b a s is o f e x p e rim e n ta l e r r o r . O bviously,
lo n g e r time, i n t e r v a l s .were n e c e s s a ry f o r th e e s ta b lis h m e n t o f e q u ilib riu m
a t low te m p e ra tu re s th a n a t h ig h te m p e ra tu re s .
When e q u ilib riu m had been re a c h e d a f i l t e r pump was a tta c h e d to
th e tu b e E, f ig u r e 3, and th e l i q u i d c o n te n ts o f r e a c tio n chamber A were r e ­
moved to f i l t e r f l a s k B by means o f tu b e 0 which had a Gooch f i l t e r p la te
h e ld i n p la c e i n th e fu n n e l by means o f th e u s u a l a s b e s to s m at. When a l l o f
th e l i q u i d had been removed» th e re s id u e was washed w ith th e d i s t i l l e d w ater
from c o n ta in e r D* P o r tio n s o f tw enty c u b ic c e n tim e te rs each were u sed f o r
th e w ashing and th e m ix tu re was shaken d u rin g th e w ashing to in s u re com plete
w ashing. A f te r each w ashing th e l i q u i d i n r e a c t i o n chamber A was removed to
"
,
I.
'
.
f i l t e r f l a s k B*, The e n t i r e a p p a ra tu s was removed from th e th e rm o s ta t and th e
l i q u i h p o r tio n i n . t h e f i l t e r f la s k . B was t i t r a t e d by means o f a s ta n d a rd iz e d
h y d ro c h lo ric a c id s o lu tio n which was ap p ro x im a te ly o n e ^ h a lf th e n o rm a lity o f
th e p o ta ssiu m h y d ro x id e u sed in th e r e a c tio n s P h e n o lp h th a le in was u sed a s an
in d ic a to r.
As a check on th e r e s u l t s , th e t i t r a t e d s o lu tio n was e v ap o rate d on
a steam p l a t e and th e dry p o ta ssiu m c h lo r id e was w eighed. The p o tassiu m
c h lo r id e c o n ta in e d a n e g lig ib le q u a n tity o f s i l v e r h y d ro x id e and s i l v e r
c h lo r id e . The e r r o r in tro d u c e d i s c a lc u la te d below;
S o l u b i l i t y p ro d u c t^ o f AgOH a t 85° i s
1 ,7 4 x 10-8'
S o l u b i l i t y p ro d u c t^ o f AgOl a t 25° i s
1.5 6 x 10-10
'
\
M ols KOH a t e q u ilib riu m i s .0022
Mols K O H /H ter i s .0022 x 40 = .088
1Q^g1
--- - = 1*97 x 10*»7,-mols Ag / liter from ^gOH''
Mols KCi at equilibrium is ,000028
Mols KCl/liter is .000028 x 40 a ,00112
15,6 x 10-11__ .n 13<_g x 10_g mols
1.12 x 10=5
I liter from AgCl
15,9 x 10-8
4 x 10
s
1 9 .7 x 10-8
4 x 10
8 4 ,925 x 10~9 D10Ig Ag i n 25 c c i from AgOH
3
e4 7 x 10-9 m olS Ag
i n 25 c.c, from AgCl
13
M o lecu lar w eight o f AgOE i s I2 4 i9
124.9 x 4 .925 x IO**9 g 4» 976 x 10^7 gm s.' AgOH
M o lecu lar w eight o f AgCl i s -143^3
* *
143 4 3 x 3 .4 7 x 10?8 viS 6 .1 5 x 10-6 gms. AgOl
'v
T o ta l w eight o f AgOH and AgOl i s .00000664:7 gms.
' ’
■
?
-»•
:
The w eighed amount o f KOl i s 0*2223 g a s .
$ e rro r is
<,000006647 d iv id e d by .2223 x 100 S
.00299 f0
■ T his shows t h a t th e e r r o r due to .the amount o f AgOH and AgCl i s
l e s s . t h a n e x p e rim e n ta l e r r o r and in a d d itio n to t h i s i f we c o n s id e r th e
common io n e f f e c t o f th e s i l v e r io n i n AgCl th e s o l u b i l i t y would be even
le s s , th a n th a t/sh o w n above. The e r r o r th e n would be s m a lle r th a n c a lc u la te d .
The amount o f s i l v e r c h lo rid e was n e g le c te d . The amount o f' potass-*
ium c h lo rid e from th e t i t r a t i o n was c a lc u la te d and t h i s was s u b tra c te d from
th e w eight o f th e d ry p o ta ssiu m c h lo r id e o b ta in e d . In t h i s manner th e amount
o f p o tassiu m c h lo r id e from th e r e a c t i o n o f s i l v e r c h lo r id e and p o tassiu m
h y d ro x id e was found* By d iv id in g th e w eight o f p o tassiu m c h lo r id e by i t s
atom ic w eight th e m ols p o ta ssiu m c h lo r id e form ed in th e r e a c t i o n were c a lc ­
u la te d and t h i s v a lu e was checked a g a in s t th e t o t a l m ols o f p o tassiu m hy­
d ro x id e u sed i n th e r e a c tio n (se e t a b l e s I , I I , and I I I ) »
T h is same p ro c e d u re was u sed w ith s ta n d a rd iz e d s o lu tio n s o f p o ta s s ­
ium hydro x id e o f v a rio u s c o n c e n tra tio n s and a t te m p e ra tu re s o f 30° $, 40° and
50° £ .0 2 5 ° . The te m p e ra tu re s were m easured by means of. a Beckmann therm ­
om eter which was s e t by means o f therm om eters g u a ra n te e d to m eet Bureau o f
S ta n d a rd s s p e c i f i c a t i o n s . The d a ta i s g iv e n on pages 14, 15 and 16.
TABLE■I
Tem perature 300 £ .0 2 5 ° a
Time o f
ran in
hours
Ti t r a t i o n
Mols KOH a t
o c » ,06925 H e q u ilib riu m
HOl
3&
■ 5
6
5§-
32.7
32.75
32.75
- 32,75
Iio ls EOH a t
Mols EOl a t
e q u ilib riu m
S ta rt.
(25ce 9 sam p le)
.002264
.002267
.002267
.002267
C o n sta n t f o r the 0*0918 N EOH s o lu tio n
4i
10
5
4
CO, »2655 ST
HOl
54.0
54.0 V
54.02
54.0
53.97
.01433
.01433
,01434
.01433
.01432
,002295
,002295
.002295
,002295
Wt. o f KQl on
e v a p o ra tio n
in grams
.000031
.000028
.000028
=000028
- — ----- ------- ------- — —
i 01452
.01452
.01452
.01452
.01452
.00019
.00019
,00018
,00019
.02284
,02284
.02284
.02284
.1792
.1741
.1737
,1742
-—
T o tal m ols KCl
on e v a p o ra tio n
Check column 4
E q u ilib ­
rium
C o n stan t
.002402
.002334
.002328
.002335
.0136*,
»0123
»0123
.0123
------------- -—------------- -,0125
1,0997
1.1026
.0 0 0 2 0
1.0855 ’
1.0973
.01474
.01478
.01464
.01455
.01471
«0132
.0132
.0125
.0132
.0139
.00030
,00030
.00030
.00029
1.7293
1.7269
I . 7434
1,7785
.02318
.02315
.02337
.02384
.0133
.0133
»0133
1 .1 0 0 1
C o n sta n t f o r the. 0.5808 H KOH s o lu tio n
5
7
s i-
o c . .531 $T
HCl
4 2.45
4 2.45
4 2 .4 5
42.47
.02254
.02254
.02254
.02255
60128
C o n sta n t f o r th e 0.9137 H KOH s o lu tio n
*These v a lu e s were n o t u sed in c a lc u la tin g th e mean f o r the e q u ilib riu m c o n sta n t sin c e i n each case
the tim e o f th e ra n was s h o r te r and e q u ilib riu m may n o t have been e s ta b lis h e d .
*
. ..TABLE I I .
Tem peratura 40° I .025°
Mols KOH a t
Time o f T i t r a t i o n
ru n in C O . .0629 N e q u ilib riu m
HCl
hours
41.0
4 1 .0
. 4 1 .0
4 0 .9 ■
6
7
Bjt
4
.002839
.002839
.002839
.002837
MDls KCl a t Wt. .o f KCl on T o ta l m ols KCl
MOls KOH a t
oh e v a p o ra tio n
e q u ilib riu m e v a p o ra tio n
s ta r t*
in
grams
Check
column 4
{25co. sam ple)
.002907
.002907
.002907
.002907
.
.000068
*000068
.000068
.000070
.003083
.002971
*003006
.002994
.*2300
.2216
.2243
.2234
C o n sta n t f o r th e 0.1163 IT KOH s o lu tio n . - —--------------------------■-— ------- ------ — ------------ —
0.2 6 5 5 H HCl
1*0959
.01469
*00035
.01452
.01417
53 o4
4
1*0900
.01451
.00055
.,01452
*01417
4-g53.4
*01472
1.0011
*00035
»01452
,01417
5 3 .4
6
1.0951
.01468
.00035
. .01452
*01417
5 3 .4 '
3*
C o n stan t f o r th e 0 .
531 H HOl
4-2.0 ■
5
4-|4 2 .0
4 2 .0 ■
6
4J2,o0
7
0
5808 H KOH s o lu tio n
E q u ilib riu m
c o n s ta n t
.0240
.0240
.0240
.0246*
. 0240
.0247
.0247
*0247
40247
---------
.
*02230
*02230 :.
.02230 . ■
.02230.; . -
*02284
.02284
.02284
.02284
C o n sta n t f o r the 0*9137 H KOH s o lu tio n
*00054
,00054
.00054
.00054
1.7538
1.7670
1.6293
1.7397
• •
.02351
*02366
.02318
.02332
,0242 '
.0242 1
.0242
*0242
----- -------- ---------— ------- ----------------- *------- — ---------— 0242
=SThis v alu e was n o t u sed in c a lc u la tin g th e mean f o r th e e q u ilib riu m c o n s ta n t sin ce th e time o f the
ru n was s h o r t e r th a n in th e o th e r c a se s and e q u ilib riu m may n o t have been e s ta b lis h e d .
D ' '
SiBLE I I I
Tem perature 50° i .025°
Mols EDL a t
Mols EOH a t MOls KOE a t
Time of T i t r a t i o n
e q u ilib riu m
s ta rt.
run in cc» «0629 B e q u ilib riu m
(25oo. sam ple)
HOl
h o u rs
12
5
8
7
51.95
3 1 .9 5
31.95
31.93.
.002295
.002295 •
.002295
.002295
.002213
.002213
=002213
.002212
C o n sta n t f o r the 0®0918 I KOH s o lu tio n
- 5
,9
7
.5
CO. .26551 HCl ■
5 4 .2
.01439
54.2
.01439
.01439
54.2
.01438
54.15
.000082
.000082
.000082
.000083
.02317
.02308
.02311
.02320
• 1732
.1723
.1729
.1737
E q u ilib riu m .
c o n s ta n t
*0370
*0370
*0370
.0375*
-.0370
--------,
■
Co. .531 I HCl
45.95
.02440
45.95
.02440
.02438 *
45.90
'.0 2 4 3 9
45.89
.00054
.00054
.00054
.00055
.01493
.01493
.01493
,01495
C o n sta n t f o r th e 0, 5808 I KOH s o lu tio n
• 6 ’'
7
8
'• 5
•
Wt. o f KCl on T o ta l mols KCl
e v a p o ra tio n
on e v a p o ra tio n
in grams
Oheok column 4
601553
601519
.01523
.01542
----- —
■ ,02531
.02531
.03531
.02531
C o n sta n t f o r the 0« 9137 I KOH s o lu tio n
1.1437,
1.1332
1.1362
1.1512
.0375
.0375
.0375
I .0582*
-.0375
,0009.1
.00091
.00093
.00092
149114
1.9176
1.9197
1.9167
.02562
.02570
,02573
■ »02569
, «,0373
.0375
.0381
.0977
---------
*These v a lu es w ere n o t used in the c a l c u l a t i o n o f the mean f o r ,t h e e q u ilib riu m c o n s ta n t sin c e the
tim e o f the run was s h o r te r and e q u ilib riu m may n o t have been e s ta b lis h e d .
17
TABLE IT .
Hewton1s v a lu e s a t 25° _ .0 2 ° *
(F or comparison)Cone, o f 0H“
m ols/K g w ater
.0939
O1011
,1098
.1072
*1038
*0997
,0978
■Gone. o f Clmt
m ols/Kg w a ter
Cone, R a tio
C l" / OH*
. .000852
,000925
,000981
,000944
»000973
,000921
.000875
,00907
,00915
»00893
,00881
,.00937
,00924
.00895
A verage f o r s o lu tio n s a p p ro x im a te ly 0 .1 H
,000471
.000483
,000465
,000481
. »000485.
,0529
.0542
.0520
,0531
,0536
A verage f o r s o lu tio n s a p p ro x im a te ly 0 .0 5 H
,00889
.00891
. .00894
.00906
»00905
——
— ------ -—•——- ,00897
* These v a lu e s were ta k e n from th e J o u rn a l o f th e A m erican Chemi c a l S o c ie ty
50, 3258 (1928)*
.
18
The e q u ilib riu m c o n s ta n ts d eterm in ed from th e data, show t h a t th e
c o n c e n tra tio n o f th e p o tassiu m h y d ro x id e h as l i t t l e o r n o .e f f e c t on th e equil*5
Ib riu m 0 The c o n s ta n ts a re in c lo s e agreem ent w ith each o th e r and e x p e rim e n ta l
e r r o r may e a s i l y ta k e c a re o f , th e d if f e r e n c e s found*
C a lc u la tio n o f th e e q u ilib riu m c o n s ta n t: ,
The r e a c t i o n we a re c o n s id e rin g may be w r itt e n
AgGl + KOH S
AgOH + KCl
The m a s s -a c tio n e x p re s s io n f o r t h i s r e a c tio n i s th e n w r itte n
' CKOH • CAgCl
"
,
The AgCls AgOH» and AggO which i s u n d o u b tab ly p re s e n t a re a l l in th e
s o l i d form and a re v e ry in s o lu b le as was shown e a r l i e r in th e d is c u s s io n . On
th e b a s is o f t h i s t h e i r c o n c e n tra tio n i s p r a c t i c a l l y a c o n s ta n t and can be
in c lu d e d a s such in th e c o n s ta n t K, When' th e common io n e f f e c t i s c o n sid e re d
th e amount o f th e s e s a l t s in s o lu tio n i s so sm all t h a t i t i s n e g lig ib le and
w ith s tro n g e r c o n c e n tra tio n s o f p o tassiu m .hydroxide th e s o l u b i l i t y d e c re a se s .
to a g r e a te r e x te n t. Many a tte m p ts have been made to d eterm in e th e s o l u b i l ­
i t y o f th e s e s a l t s b u t th e v a lu e s g iv en by v a rio u s e x p e rim e n te rs v a ry so
w id ely t h a t th e agreem ent i s in m agnitude o n ly . E r r o r s a re so la r g e due to
th e sm all amount o f th e s e s a l t s t h a t go in to s o l u t i o n .t h a t th e v a lu e s a re
alm o st u s e le s s and w i l l rem ain so u n t i l more a c c u ra te m ethods o f a n a ly s is
can be dev elo p ed . The s i l v e r hydro x id e and th e s i l v e r c h lo r id e in th e above
e q u a tio n w i l l th e n be. c o n sid e re d a s c o n s ta n t and th e new m a s s -a c tio n equa^
t'io n w i l l be w r itt e n
qKCI _
Qkoh “
»
K*
The mo'ls o f p o tassiu m h y d ro x id e which i s added a t th e s t a r t of
19
th e r e a c tio n i s known and by t i t r a t i o n w ith a s ta n d a rd h y d ro c h lo ric a c i d , s o l ­
u tio n a t e q u ilib riu m th e mods o f p o ta ssiu m h y d ro x id e a t e q u ilib riu m may be
d e term in e d . The d if f e r e n c e i n th e s e amounts w i l l th e n be th e moI s o f potass**
ium c h lo rid e form ed in th e r e a c t i o n . The e q u ilib riu m c o n s ta n t i s th e n ob­
ta in e d . by d iv id in g th e c o n c e n tra tio n o f p o tassiu m h y d ro x id e i n m ols p e r
l i t e r limtb- th e c o n c e n tra tio n o f p o ta ssiu m c h lo rid e i n m ols p e r l i t e r a t
e q u ilib riu m *
A re v ie w o f th e t a b l e s w i l l show t h a t th e c o n s ta n t o b ta in e d f o r
th e 0.0918 K KOH s o lu tio n a t 30° Z .0 2 5 ° i s th e o n ly one t h a t v a r ie s to any
g r e a t e x te n t from th e v a lu e s w ith th e o th e r c o n c e n tra tio n s a t th e same temp­
e r a t u r e . The t o t a l c o n c e n tra tio n s o f p o ta ssiu m hy d ro x id e and p o tassiu m
c h lo r id e a re u se d i n c a lc u la tin g th e c o n s ta n ts . T h is in v o lv e s th e assump­
t i o n t h a t th e s e su b sta n c e s a re 100$ d is s o c ia te d in s o lu tio n s an assum ption
w hich c e r t a i n l y can n o t be j u s t i f i e d e i t h e r from th e s ta n d p o in t o f th e o ld ­
e r e l e c t r o l y t i c d is s o c ia tio n th e o ry o r from t h a t o f th e newer in t e r i o n i c
a t t r a c t i o n th e o ry a s a p p lie d to s tro n g e le c tr o ly te s *
W hile i t i s r e a l i z e d t h a t th e a c t i v i t i e s o r " e f f e c t i v e c o n ce n tra ­
tio n s " o f th e io n s in v o lv e d i n t h i s e q u ilib riu m sh o u ld be u sed in c a l c u l a t ­
in g th e v a lu e s o f th e e q u ilib riu m c o n s ta n ts th e d i f f i c u l t y a tte n d in g th e
e v a lu a tio n o f t h e ' in d iv id u a l a c t i v i t i e s i n such a system a re g r e a t enough
to p re c lu d e such a c a l c u la tio n a t t h i s tim e .
However» u s in g th e h y p o th e s is o f th e in d ep en d en t a c t i v i t y co­
e f f i c i e n t s o f th e ions*’ , v iz , — " I n d i l u t e s o lu tio n s th e a c t i v i t y c o e ff­
i c i e n t o f any io n depends s o le l y upon th e t o t a l io n ic s tr e n g th o f th e s o l­
u tio n " — and u s in g th e d a ta g iv e n i n th e same r e f e r e n c e f o r h y d ro x y l and
20
c h lo r id e io n s a t io n ic s tr e n g th o f 0'«1 m o la l s o lu tio n a s b e in g com parable
w ith th e 0*0918. U KOH s o lu tio n u sed i n t h i s work i t i s found 't h a t th e ac**
t i v i t y o f th e h y d ro x y l io n i s 0 o81 and th a t o f th e c h lo rid e io n
0»79«,
T h is means t h a t o n ly 0 .8 1 o f th e t o t a l h y d ro x y l io n c o n c e n tra tio n m easured
a n a l y t i c a l l y i s e f f e c t i v e a t e q u ilib riu m and t h a t only 0 .7 9 o f th e t o t a l
c h lo r id e io n a s m easured a n a l y t i c a l l y i s e f f e c t i v e a t e q u ilib riu m . In o th e r
words o n ly 0 .8 1 o f th e h y d ro x y l io n s p o t e n t i a l l y a v a ila b le and o .7 9 o f th e
c h lo r id e io n s p o t e n t i a l l y a v a ila b le i n s o lu tio n a re a c tu a lly in v o lv e d i n
th e e q u ilib riu m *
T h is means t h a t " i n o r d e r to a r r i v e a t th e more e x a c t v a lu e o f th e
e q u ilib riu m c o n s ta n t where th e 0*0918 H KOH s o lu tio n i s in v o lv e d th e e q u il­
ib riu m c o n s ta n t g iv en i n th e t a b l e s sh o u ld be m u ltip lie d by 0.79/0*81» T h is
would g iv e a s e r i e s o f v a lu e s ru n n in g about 2*5% low er th a n th o s e ta b u la te d
above*
The h y p o th e s is o f th e in d ep en d en t a c t i v i t y c o e f f i c i e n t s o f th e io n s
s t a t e d above c o n ta in s th e r a t h e r vague p h ra s e " d i l u t e s o lu tio n s " . In a case
l i k e t h i s some e x p la n a tio n o f th e p h ra se seems n ecessary * Lewis and Randall^-'
comment a s fo llo w s , "When we u se th e r a t h e r vague p h ra se " d i l u t e s o lu tio n s "
i n a c ase l i k e t h i s we mean t h a t th e p r i n c i p l e a s s ta t e d ap p ro ach es com­
p l e t e v a l i d i t y a s th e d i l u t i o n i s i n d e f i n i t e l y in c re a s e d . I t becomes th e n a
m a tte r o f experim ent to determ in e a t what c o n c e n tra tio n s such a p r in c ip le
may be re g a rd e d a s v a l i d w ith in c e r t a i n l i m i t s o f p e rm is s ib le e rro r* say 1$*.
W ith such an i n t e r p r e t a t i o n i t ' i s o u r b e l i e f th a t, th e h y p o th e s is i s c o r r e c t
\
.
■ 1
’
-
'
o v e r th e same ran g e a s o u r p re v io u s r u l e o f m ixture* nam ely, up to an io n ic
s tr e n g th o f a few h u n d re d th s to a few t e n t h s , a c c o rd in g to th e n a tu re o f
SI
th e io n s ,'T h e degree o f d e p a rtu re in c o n c e n tra te d s o lu tio n s d o u b tle s s de­
pends upon numerous f a c t o r s , such a s th e amount o f h y d ra tio n of. th e ion®"
t
W hile t h i s r u le can be a p p lie d in s o lu tio n s c o rre sp o n d in g to th e
0,'0918 N KOH s o lu tio n u sed h e re i t i s d o u b tfu l i f i t ban be ex ten d ed to
’
in c lu d e even ap p ro x im a te ly 0 .5 N KOH s o lu tio n s a lth o u g h f u r t h e r exper­
im e n ta tio n i n c o n n e c tio n w ith t h i s work may show t h a t th e "few te n th s " o f
th e above q u o ta tio n may prove to be a s many a s f i v e t e n t h s . T h is i s a poss=i b i l i t y to which we can do no more th a n c a l l a t t e n t i o n a t t h i s p o in t.
B ecause o f th e u n c e r ta in ty in v o lv e d i n a tte m p tin g to e v a lu a te th e
a c t i v i t i e s o f th e io n s in th e more c o n c e n tra te d s o lu tio n s i t i s f e l t t h a t i t
i s b e t t e r to p r e s e n t th e a c t u a l l y d eterm in ed v a lu e s o f t o t a l c o n c e n tra tio n
o f th e io n s from w hich th e n e c e s s a ry a c t i v i t y d a ta cah be o b ta in e d a s soon
a s a s u ita b le and s a t i s f a c t o r y tre a tm e n t o f th e c o n c e n tra te d s o lu tio n s o f
th e s tro n g e l e c t r o l y t e s a re a v a i l a b l e i . l t i s p o s s ib le t h a t t h i s d a ta i s
a v a ila b le ^ f o r a l l th e c o n c e n tra tio n s in v o lv e d b u t c o n s id e ra b le work w i l l
have to be done, in o rd e r to a r r i v e a t v a lu e s which w i l l ap p ly to th e e x ac t
c o n c e n tra tio n s and te m p e ra tu re s in v o lv e d i n t h i s s tu d y . I t i s a g a in emphas iz e d t h a t s u f f i c i e n t d a ta a re a v a ila b le ? f o r th e 0.0918 N KOH s o lu tio n
and p o s s ib ly a ls o f o r th e 0.5808 N and th e 0.9157 N KOH s o lu tio n s and when
ta k e n to g e th e r w ith th e d a ta o f t h i s p a p e r, would allow o f a c a lc u la tio n o f
th e e q u ilib riu m c o n s ta n ts in term s o f th e more s i g n i f i c a n t a c t i v i t y r a tio s *
THE HEAT OF THE REACTION
In th e stu d y o f th e chem ical k i n e t i c s o f a r e a c tio n n o th in g i s o f more
i n t e r e s t o r o f more im portance th a n th e energy changes in v o lv e d i n th e
28
a c ti o n . The chem ical energy in v o lv e d in a chem ical r e a c tio n c a r r i e d ou t
u n d er th e c o n d itio n s o f t h i s stu d y (namely, in s o lu tio n and u n d er co n d i­
tio n s where none o f th e r e a c t a n t s ap p ear a s v o l a t i l e g a s e s , and no l i g h t i s
absorbed o r l i b e r a t e d and no e l e c t r i c a l en erg y i s absorbed o r lib e r a te d ) i s
absorbed o r ev o lv ed alm ost e n t i r e l y i n th e form o f h e a t.
F o r a long tim e i t was assumed t h a t th e h e a t ev o lv ed in a chem ical
r e a c tio n was a d i r e c t m easurem ent o f th e ch em ical a f f i n i t y o f th e v a rio u s
r e a c t a n t s f o r each o th e r , t h a t i s , i f a la r g e amount o f h e a t was li b e r a t e d
i n a r e a c tio n th e r e was a la r g e a f f i n i t y d is p la y e d by. th e r e a c tin g atoms o r
m o le c u le s . On th e o th e r hand i f sm all th e rm a l e f f e c t s accom panied a r e a c tio n
th e atoms o r m o le c u les in v o lv e d were s a id to have sm all a f f i n i t y . While t h i s
i s known to be tr u e o nly i n a q u a l i t a t i v e sen se and a n o th e r p h y s ic a l q u a n tity
th e change i n f r e e energy o f a system , i s to be tak en a s th e q u a n tita tiv e
m easure o f chem ical a f f i n i t y , th e th e rm a l e f f e c t s accompanying chem ical
change a re s t i l l o f prim e im portance* I n f a c t th e whole stu d y o f chem ical
therm odynam ics and o f th e rm o -c h e m istry i s b a se d upon th e h e a t changes accom­
panying chem ical r e a c tio n .
C a lc u la tio n o f th e . h e a t o f th e re a c tio n .:
A v e ry im p o rtan t e q u a tio n is. u sed f o r c a lc u la tin g h e a ts o f r e a c tio n
from th e e q u ilib riu m c o n s ta n ts m easured a t two d i f f e r e n t te m p e ra tu re s and i t
was d e riy e d by v a n ’t Hoff* The u n in te g ra te d e x p re ssio n h a s th e fo llo w in g
:
form :
d In K
dT
-
. -AH '
RT3
where K i s th e e q u ilib riu m c o n s ta n t, T th e a b s o lu te te m p e ra tu re , R th e m olar
g as c o n s ta n t and ■&H th e h e a t o f th e r e a c tio n *
■
'r,
\
'
>
'
23
T his e x p re ss io n can h e - in te g r a te d - i f SH i s c o n s ta n t to g iv e the
fo llo w in g forms
-jpg— Zr
AE
9% %
% %
where Kg i s th e e q u ilib riu m c o n s ta n t a t tem p eratu re Tg and. K^ i s th e e q u il■
ih riu m c o n s ta n t a t te m p eratu re
and H and AH have th e same, s ig n if ic a n c e
a s b e f o r e , and. a re m easured i n calo ries®
By. means o f t h i s e q u a tio n i t i s p o s s ib le to c a lc u la te th e h e a t
o f the r e a c tio n i f the e q u ilib riu m c o n s ta n ts a t two d i f f e r e n t te m p e ratu res
a re known, o r i f the e q u ilib riu m c o n s ta n t a t one tem p eratu re and. the h e a t
o f th e r e a c tio n a re known, th e e q u ilib riu m c o n s ta n t a t a n o th e r temper­
a tu r e may be c a lc u la te d . In most o a s e s , how ever, AH is" n o t c o n s ta n t over
a very lo n g te m p e ratu re range so t h a t one m ust be c a r e f u l n o t to ap p ly th e
e q u a tio n o v er e x c e s s iv e ly la rg e te m p e ratu re i n t e r v a l s . The tem p eratu re
i n t e r v a l u s u a lly employed i s 10° 0 , i t h a v in g b e e n l found t h a t the e q u a tio n
h o ld s f a i r l y w e ll due to the f a c t th a t the v alu e o f AH does n o t change
g r e a tly in such an i n t e r v a l . " I t i s em phasized, how ever, t h a t the e q u atio n
i s s t r i c t l y a p p lic a b le o nly i n c a s e s where AH i s a c o n s ta n t, t h a t i s , where
a p l o t o f th e lo g a rith m s o f th e e q u ilib riu m c o n s ta n ts a g a in s t the recipro**
c a l o f th e c o rre sp o n d in g a b s o lu te te m p e ra tu re s i s a s t r a i g h t lin e * For
c a s e s where AH i s n o t a c o n s ta n t" th e acc u ra cy o f the d a ta c a lc u la te d from
the e q u a tio n becomes in c r e a s in g ly more a c c u ra te as the te m p e ra tu re in te r *
v a l decreases®
_i
When -the e q u ilib riu m c o n s ta n t d a ta ’ o f t h i s p a p e r a re s u b s t i t u t e d *
in to th e e q u a tio n i t ’i s found t h a t AH i s f a r from c o n s ta n t, b u t i t i s
found to d e c re a se q u ite r a p id ly as th e tem p eratu re r i s e s .
24
The h e a t o f th e r e a c tio n was c a lc u la te d a s shown i n . t h e sample
c a lc u la tio n g iv e n helow :
-
-
H e fe rin g to the ta b le on page 25 f o r th e 0.0918 E KOH s o lu tio n a t 300
to 40° « .0250 the v a lu e s may be o b ta in e d f o r Tg, T1 , Kg and K1 . S u b s t i t u t ­
in g these, v a lu e s in v an ’ t H o ff’ s e q u a tio n iso ch o re we have
2.303 log
60240
.0123
L 4H_ 313 - 303
" % ' 313 x 303
Upon so lv in g th e above e q u a tio n f o r AH we have
An
M
«
46 606 ( I Qg .'i>r0 2 4 0 .^ y l0 g .0 1 2 3 ) 503 x 313
^1B - 303
•SH = 12, 656 c a lo r ie 's p e r mol*
The fo llo w in g ta b le c o n ta in s the v a lu e s o f th e h e a t o f th e reac-*
tio n a t d i f f e r e n t te m p e ra tu re s a s c a lc u la te d from th e d a ta o f t h i s p a p e r
and from th e v alu e o f K o b ta in e d by Hewton^ a t 2 5 ° '£ *020«
. TABLE Vo
C a lc u la te d h e a t o f th e re a c tio n *
30° to 40° £ *025°
KOH S o lu tio n
0*0918 M
0.5808 N
0.9137 F
K2
. K1
T2
.0240
60247
.0242
.0123
.0132
.0133
313
315
313
O
§
0.0918 F
0.5808 F
0*9131 H
.0370
*0375
a 0376
.0240
.0247
.0242
Ti
'
303
303
■303
Heat o f r e a c tio n
c a l o r i e s / mol
12,656
11,871
11,351
to 50° £ .0 2 5 °
323
323
323
-315
313
313
8,73% r' .
. 8,441
6*889■
25
50° to 50° + .0 2 5 °
EOH S o l u t i o n .
0.0918 IT
0.5808 IT
0.9137 E
Ei
K2
,0370
.0375
.0576
Ti
*2
.0123 ■ - 1 # .
.0132
323
323 ■
*0133
303
303
303
■ H e a f 'o f r e a c tio n
c a l o r i e s / mol
10,756 '
10,220
10,177
■ ITewtonf s d a ta f o r Ool E and .0 5 E KOH s o lu tio n s a t 250 ± ,02°
A u th o r’ s d a ta f o r 0 . 0918 E and .5808 E KOH s o lu tio n s a t 30° ± .025°
KOH S o lu tio n
Approx* 0 .1 E
Eewton 0 .0 5 E
A uthor 0.5808 E
Kg
.0123
- —~
.0132
Ki
.00905
.00897
T2
T1
303
298
298
----
303
H eat o f" r e a c tio n
c a l o r i e s / mol
11,035
*15,916
* In t h i s c a l c u l a t i o n th e c o n s ta n t o b ta in e d by Hewton f o r the
0 .0 5 IT s o lu tio n was u sed as shown above w ith th e c o n s ta n t o b ta in e d by
th e a u th o r f o r the 0.5808 IT s o lu tio n . I t appears, th a t t h i s com parison
can, be made sin ce the c o n c e n tra tio n o f the s o lu tio n seems to have such a
sm all e f f e c t bn the e q u ilib riu m . The v alu e .00897 was s u b s t i t u t e d f o r
and the c o rre sp o n d in g a b s o lu te tem p eratu re Tp i s 2989 The v a lu e .0152
was s u b s tit u te d f o r Eg and i t s c o rre sp o n d in g a b s o lu te te m p e ratu re i s 305?
The v alu e o b ta in e d f o r th e h e a t o f the r e a c tio n seems to ag ree f a i r l y
w e ll w ith the v a lu e s o b ta in e d a t th e o th e r tem peratures*
/
26
Q u a lita tiv e l y the d a ta means t h a t th e r e a c tio n in q u e stio n
AgOl + KOH = KQl 4- AgOH
a b so rb s h e a t when going in th e forw ard d i r e c t i o n and i s favored" by r a i s i n g
the te m p e ra tu re . Q u a n tita tiv e ly it.m e a n s t h a t d H d e c re a se s from c lo se to
I S 9OOO c a l o r i e s p e r mol a t 25° O to ab o u t 8,500 c a lo r ie s p e r mol a t 50° Co
Here a g a in the v a lu e s o f K sh o u ld be th o se c a lc u la te d on the
b a s is o f a c t i v i t i e s in s te a d o f t o t a l m o lar c o n c e n tra tio n s b u t in the ab senoe o f a c t i v i t y d a ta f o r the more c o n c e n tra te d s o lu tio n s th e e q u ilib riu m
c o n s ta n ts p re s e n te d b e fo re w i l l be u se d . I n th e case o f the 0.0918 H KOH
s o lu tio n i t i s p o s s ib le to c a lc u la te A E u s in g th e v a lu es o f K e v a lu a te d
in term s o f a c t i v i t i e s b u t a f t e r a l l t h i s p ro b a b ly would have b u t l i t t l e
e f f e c t on th e v alu e o f AH inasmuch a s i t i s th e r a t i o o f two e q u ilib riu m
c o n s ta n ts w hich i s in v o lv e d in th e c a l c u l a t i o n o f AH and inasm uch as the
d if f e r e n c e s in th e a c t i v i t i e s a t two d i f f e r e n t te m p e ratu res IO0 a p a r t
would p ro b a b ly n o t be g r e a t l y d i f f e r e n t . Or i f th e a c t i v i t i e s o f the io n s
do change, t h a t o f one io n w o u ld 'p ro b a b ly change to ab o u t th e same e x te n t
a s the o th e r and the r a t i o o f the c h lo rid e io n to the hy d ro x y l io n would
be p r a c t i c a l l y the same. I t i s b e lie v e d th a t the v a lu es o f AH o b ta in e d
from a t i t i v i t i e s w i l l n o t be g r e a t l y ^ i f f e f e n t from th o se p re s e n te d in t h i s
"
* 1*
paper* T his i s a p o in t w hich fu tu r e stu d y w i l l have to s e t t l e .
T e t z l a r and H eroy0 and G regory and Mohrs r e p o r t th a t a t the b o i l *
,
Ing p o in t o f the s o lu tio n m ost o f th e s i l v e r c h lo rid e can be co n v erted to
s i l v e r oxide o r in o th e r words the r a t i o o f th e c h lo rid e io n to th e hydroxyx io n i s h ig h . I f t h i s i s tru e i t means t h a t th e v alu e o f th e e q u ilib riu m
c o n s ta n t m ust in c re a s e r a p id ly as th e te m p e ratu re i s r a is e d above 50° f o r
a t t h i s te m p e ratu re the r a t i o o f the c h lo r id e .io n to the hydroxyl io n i s
27
only 0o03'75, a v a lu e o nly f o u r tim es l a r g e r th an t h a t a t 25° and a v ery
sm all v alu e i n c o m p a riso n 'to what i t m ust he a t 95° 0 .
SUMfARY
I.
The r e a c tio n AgOl + EDH = EDI + AgOH was c a r r ie d ou t a t 30°,.
40°» and 50° u s in g d i f f e r e n t c o n c e n tra tio n s o f aqueous p o ta ssiu m hydroxide
and the Q qU ilihrium c o n s ta n ts were o b ta in e d .
2.
I t was found t h a t th e c o n c e n tra tio n o f p o ta ssiu m hydroxide
u sed had l i t t l e i f any e f f e c t on the e q u ilib riu m o f th e r e a c tio n .
3.
The h e a t o f the r e a c tio n a t th e v a rio u s te m p e ra tu re s was c a l ­
c u la te d by u s e o f v a n 't H o f f 's r e a c tio n is o c h o re e q u a tio n .
4.
The h e a t o f the r e a c tio n w as.fo u n d to d e crea se q u ite r a p id ly
a s th e te m p eratu re was in c re a s e d .
Se
Com parisons a re g iv e n w ith d a ta s u b m itte d .b y Hewton,® and
th e h e a t o f th e r e a c tio n c a lc u la te d by u se o f th e above m entioned d a ta .
6o
D ata w i l l have to be sec u re d f o r th e a c t i v i t i e s o f io n s in s o l­
u tio n s of h ig h e r c o n c e n tra tio n b e fo re the tr u e e q u ilib riu m c o n s ta n ts f o r
th e se s o lu tio n s can be d eterm in ed .
The a u th o r w ish es to take t h i s space to e x p re ss h i s a p p re c ia tio n
to D r. Re H.. M elavenil Dz;. ;0. S . S heppard, D r. B. I , Jo h n so n , and P r o fe s s o r
Po Ge G aines o f the c h e m istry d e p artm en t, and Mr. J e s s e Green, o f the
Montana S ta te C ollege A g r ic u ltu r a l E xperim ent S ta tio n f o r th e tim e , a s s i s t ­
a n c e , and. i n s p i r a t i o n they have g iv e n him d u rin g th e y e a r w h ile the above
w ork was being c a r r i e d to c o m p letio n .
28
tlTBRA W B QimD
I , I n t e r n a t i o n a l Q r i t i c a l T ables,, 1 s t B d itlo n 9 McG-raw H i l l iS ook Goe , 1@ 28..
Vol= V I, 255*8%,
'
,
Se le w is and H a n d a ll9 Thermodynamies an d th e Vree Energy o f Chemical Subs ta n c e s , 1 s t B d itio n 9.MoGraw H ill,B o o k .C o ® ,.1 3 2 3 ,' SSO-SSi :
*
'•
3 , Boy Vo Bewton9 J 9 Am, Chem9 Soce SQa 3258-61 (1 9 2 8 ),
4» Boyes and E o h r9 J e Ame Ghem, Soc= 2 4 , 1141-48 (1 9 0 2 ),
5. M e llo r9 A Oomprehenslve T r e a tis e on In o rg a n ic and T h e o r e tic a l- Ohemistry®
Longmans and Go», V ble' I l I 9 378»
O rig in a l references:
G» W e tz la r9 Schw eiggareS - J o u r n a l'23, 99 (1828),
Jo P e rc y , S i l v e r and G old, London I., 10 (1 8 8 0 ),
6 , I b id
Vole I l I 9 372.
-
O r ig in a l re f e r e n c e s :
?/, G reg o ry , P h i l , Mag, 9 (2 ) , 19,. 349 (1 8 7 3 ).
P , Mohr9 L ie M g flS Ann=, 6 6 , SG (1 8 4 8 ).
7» T a y lo r, A T r e a tis e on P h y s ic a l C h em istry , 2nd E d itio n , B» fan B o stran d
C o ,, 1931, Vole I , 763-75«