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A critical study of the application of the soap titration method to the determination of calcium and magnesium

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A critical study of the application of the soap titration method to the determination of calcium and magnesium

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Content A CRITICAL STUDY OF THE APPLICATION OF THE
SOAP TITRATION M ETHOD., TO THE DETERMINATION
OF CALCIUM AND MAGNESIUM
A T h e s is
P r e s e n t e d to
th e F a c u l t y o f t h e D e p a rtm e n t o f C h e m is try
U n i v e r s i t y o f S o u th e r n C a l i f o r n i a
I n P a r t i a l F u l f i l l m e n t
o f t h e R e q u ire m e n ts f o r t h e D e g ree
M a s te r o f A r t s
by
Edward Jo h n B a l l
J u l y 1939
UMI Number: EP41513
All rights reserved
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UMI EP41513
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
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This thesis, written by
Edw ard J . B a ll
under the direction of h % .® ~ Faculty Committee,
and a p p ro ved by all its m em bers, has been
presented to and accepted by the Council on
Graduate Study and Research in partial fulfill
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■ M a s te r o f A r t s
D ean '
Secretary
Date.
Faculty Com m ittee
Chairman
TABLE OF CONTENTS
P a g e
I n t r o d u c t i o n .............................. 1
F a c t o r s f o r I n f l u e n c i n g t h e A c c u ra c y o f th e
D e t e r m in a t io n ........................................................................................ 3
P r e p a r a t i o n o f S ta n d a r d S o l u t i o n s .................................... . 4
M ethod o f T i t r a t i n g ........................................................ 7
B la n k D e te r m in a tio n 7
G raph o f t h e T i t r a t i o n C u rv e s . .......................................... 10
A c c u ra c y D e t e r m in a t io n s ................................................................... 12
Summary an d C o n c lu s io n s ................................................................... 14
B i b li o g r a p h y .................................................................................................. 17
INTRODUCTION
A p r o c e d u r e i n u s e f o r d e t e r m i n i n g h a r d n e s s o f w a t e r
i s by u s i n g a s t a n d a r d so a p s o l u t i o n t o p r e c i p i t a t e t h e c a l
cium an d m agnesium i o n s a s s a l t s o f t h e h i g h e r f a t t y a c i d s .
A f t e r t h e c a lc iu m and m agnesium i o n s p r e s e n t a r e p r e c i p i t a t e d ,
th e n a s l i g h t e x c e s s o f so a p form s a p e rm a n e n t l a t h e r when
t h e sa m p le i s s h a k e n . T h is i s t h e end p o i n t . S h o u ld am o u n ts
o f i r o n , s t r o n t i u m , c o p p e r , and o t h e r c a t i o n s t h a t form i n
s o l u b l e so a p s b e p r e s e n t , th e y a l s o w ould be p r e c i p i t a t e d by
th e s t a n d a r d s o l u t i o n . H ow ever, t h e s e l a t t e r io n s o c c u r in
v e r y s m a ll q u a n t i t i e s i n w a t e r , and i t i s u s u a l l y assum ed
t h a t th e h a r d n e s s i s d u e t o t h e c a lc iu m an d m agnesium .
T h is m ethod w as w o rk ed o u t an d p u b l i s h e d by D r. T.
C l a r k 1 i n w h ic h he d e te r m in e d by t r i a l how much o f t h e s t a n d
a r d so a p s o l u t i o n w as r e q u i r e d f o r p o r t i o n s o f w a te r o f known
h a r d n e s s . H is m ethod was t o t a k e w a t e r sa m p le s o f 70 m l
w h ic h was c a l l e d a m i n i a t u r e g a l l o n . T h is am ount w as t a k e n
t o f a c i l i t a t e c a l c u l a t i o n s , s i n c e t h e r e a r e a s many m i l l i g r a m s
o f w a t e r i n 70 m l a s t h e r e a r e g r a i n s i n a n I m p e r i a l g a l l o n .
The s t a n d a r d so a p s o l u t i o n t h e n was made t o s u c h a c o n c e n t r a
t i o n t h a t 1 m l p r e c i p i t a t e s 1 m i l l i g r a m o f c a lc iu m c a r b o n a t e .
T hus t h e m i l l i l i t e r s o f s t a n d a r d so a p u s e d f o r t h e sa m p le
1 Chem. G a z ., ^100 (1847)
w ould b e i t s d e g r e e 2 o f h a r d n e s s .
A m o d if ie d m ethod f o r t h i s h a r d n e s s d e t e r m i n a t i o n i s
one i n w h ic h t h e m agnesium i o n s a r e made t o form a com plex
io n w i t h t h e t a r t r a t e r a d i c a l an d t h u s a r e n o t p r e c i p i t a t e d
by t h e s t a n d a r d so a p s o l u t i o n . A f t e r a d d in g t h e t a r t r a t e
and t i t r a t i n g , t h e volum e o f so a p u s e d w i l l b e i n d i c a t i v e o f
t h e c a lc iu m p r e s e n t . Then a n o t h e r a l i q u o t i s t i t r a t e d i n
w h ic h t h e r e i s no t a r t r a t e , a n d t h i s volum e w i l l be i n d i c a t i v e
o f t h e c a lc iu m and t h e m ag nesium . The d i f f e r e n c e i n volum e
o f t h e two w i l l b e t h e am ount o f m agnesium i n t h e a l i q u o t
ta k e n f o r a n a l y s i s . T hus t h e am ount o f c a lc iu m and m agnesium
may b e d e te r m in e d e n t i r e l y v o l u m e t r i c a l l y .
S ta n d a r d p r o c e d u r e s f o r t h e d e t e r m i n a t i o n o f c a lc iu m
and m agnesium a r e th o s e i n w h ic h t h e c a lc iu m i s p r e c i p i t a t e d
a s t h e o x a l a t e i n a n a l k a l i n e s o l u t i o n ; f i l t e r e d an d i g n i t e d
t o t h e o x i d e . The m agnesium i s u s u a l l y p r e c i p i t a t e d a s t h e
m agnesium ammonium p h o s p h a te i n a s o l u t i o n c o n t a i n i n g one
t e n t h i t s volum e o f c o n c e n t r a t e d a q u e o u s ammonia ( s p . g r .
0 . 9 0 ) , f i l t e r e d an d i g n i t e d and w e ig h ed a s m agnesium p y r o
p h o s p h a te . E ac h o f t h e s e p r o c e d u r e s i s r a t h e r l e n g t h y .
The r a p i d i t y w i t h w h ic h t h e so a p t i t r a t i o n f o r m agne
siu m an d c a lc iu m c o u ld b e a c c o m p lis h e d a p p e a l s s t r o n g l y t o
t h e a n a l y s t , so i t w as d e c id e d t o i n v e s t i g a t e w h at a c c u r a c y
2 The E n g l i s h d e g r e e , g r a i n s o f c a lc iu m c a r b o n a t e p e r
I m p e r i a l g a l l o n .
c o u ld b e e x p e c te d from t h i s m e th o d . I f t h e acc u ra c y : w a r
r a n t e d , t h e n t h i s m ethod m ig h t b e a d a p te d t o r o c k a n a l y s i s
e s p e c i a l l y w h ere t h e a s s a y f o r c a lc iu m an d m agnesium w ould
b e lo w , and i n t e r f e r i n g io n s c o u ld be e l i m i n a t e d .
FACTORS FOR INFLUENCING THE ACCURACY OF THE DETERMINATION
I n r e a d i n g t h e l i t e r a t u r e on t h i s s u b j e c t t h e r e seem s
t o be a c o n f l i c t o f o p i n io n a s t o t h e a c c u r a c y and v a l i d i t y
o f t h i s so a p t i t r a t i o n i n q u a n t i t a t i v e a n a l y s i s . R e p o r ts
t h a t i f t h e p r o c e d u r e i s p r o p e r l y e x e c u te d t h e n a n a c c u ra c y
o f 10 t o 15 p a r t s p e r m i l l i o n on w a t e r a s h a rd a s 300 p a r t s
may be o b t a i n e d h a v e b e e n m ade. T h is d a t a r e f e r s t o a
s t r a i g h t t i t r a t i o n w h ere t h e t o t a l h a r d n e s s was d e te r m in e d .
An a r t i c l e by R. H. F e a n and H. G u s ta f s o n 3 g i v e s t h e
f o l l o w i n g f a c t o r s a s i n f l u e n c i n g t h e a c c u r a c y o f t h e d e t e r
m in a t i o n : t e m p e r a t u r e o f t h e s o l u t i o n an d t h e f r e e c a rb o n
d i o x i d e . The t e m p e r a t u r e i s a v e r y im p o r ta n t f a c t o r and
s h o u ld b e c o n s i d e r e d . W ith a d e c r e a s e in t e m p e r a t u r e t h e r e
i s a n i n c r e a s e o f h a r d n e s s an d i t d o e s n o t seem t o d ep en d on
t h e am ount o f h a r d n e s s , b u t on t h e volum e o f t h e s o l u t i o n .
T h e re i s a n i n c r e a s e o f t h e r e q u i r e d so a p s o l u t i o n w i t h a n
3 I n d . a n d E n g r. C h em ., A n a l y t i c a l E d i t i o n , V o l. 3 ,
3 5 5 -3 5 6 (1 9 3 1 } .
i n c r e a s e o f f r e e c a rb o n d i o x id e i n t h e sa m p le t o be t i t r a t e d .
T h is c a rb o n d i o x i d e f a c t o r c a u s e s a g r e a t e r v a r i a t i o n i n a
s o f t w a t e r th a n i n a h a r d w a t e r .
I n o r d e r t o e l i m i n a t e t h e t e m p e r a t u r e f a c t o r , a c o n
s t a n t te m p e r a t u r e o f 22 d e g r e e s c e n t i g r a d e was m a in ta in e d i n
a l l o f t h e f o l lo w in g d e t e r m i n a t i o n s . I n o r d e r t o e l i m i n a t e
th e f r e e c a rb o n d i o x i d e and a c i d i t y t h e s o l u t i o n s w ere
r e n d e r e d b a s i c w i t h ammonium h y d r o x i d e .
PREPARATION OF STANDARD SOLUTIONS
P r e p a r a t i o n o f so a p s o l u t i o n : 20 gram s U .S ;P . c a s t i l e
so a p w e re d i s s o l v e d i n 1 l i t e r o f 95 p e r c e n t e t h y l a l c o h o l
an d 1 l i t e r o f d i s t i l l e d w a t e r . The so a p s o l u t i o n was a llo w e d
t o s t a n d f o r t w e n t y - f o u r h o u r s i n o r d e r t o l e t any i n s o l u b l e
m a t t e r s e t t l e . The s o l u t i o n was t h e n f i l t e r e d . T h is s o l u t i o n
w as t h e n s t a n d a r d i z e d , w i t h t h e s t a n d a r d c a lc iu m s o l u t i o n . The
compounds fo rm ed by t h e a c t i o n o f t h i s so a p s o l u t i o n on c a l
cium io n s w e re t h e i n s o l u b l e o l e a t e s (C^HggGOO) g C a, l i n o -
l e a t e s (Cp^Hg^COO)g G a, an d p a l m i t a t e s (C^gHg^COO)g Ca.
P r e p a r a t i o n o f t h e s t a n d a r d c a lc iu m s o l u t i o n : 1 .0 1 8 5
gram s o f c a lc iu m c a r b o n a t e w ere w e ig h ed o u t and d i s s o l v e d
w i t h d i l u t e h y d r o c h l o r i c a c i d . As a p r e c a u t i o n a w a tc h g l a s s
was c o n s t a n t l y k e p t o v e r t h e b e a k e r w h i l e d i s s o l v i n g , s i n c e
5
th e r a t h e r v i g o r o u s . e b u l l i t i o n m ig h t s p l a t t e r some s o l u t i o n .
o u t . The s o l u t i o n now c o n t a i n i n g t h e c a lc iu m c h l o r i d e was
e v a p o r a t e d t o d r y n e s s on a w a t e r b a t h . The c r y s t a l l i z e d
s a l t s w e re t h e n d i s s o l v e d i n a b o u t 10 m l o f d i s t i l l e d w a te r
an d a g a i n e v a p o r a te d t o d r y n e s s t o i n s u r e t h e e x p u ls io n o f
t h e h y d r o c h l o r i c a c i d . The s a l t s w e re d i s s o l v e d an d t h e
s o l u t i o n d i l u t e d up t o 1 l i t e r . C a l c u l a t i o n from t h e am ount
o f c a lc iu m c a r b o n a te u s e d g a v e a c o n c e n t r a t i o n o f 0 .0 2 0 4
n o r m a l.
P r e p a r a t i o n o f t h e s t a n d a r d m agnesium s o l u t i o n : 3 .3 3 0
gram s o f h y d r a te d m agnesium c h l o r i d e w e re d i s s o l v e d an d t h e
r e s u l t i n g s o l u t i o n d i l u t e d up t o 1 l i t e r . S in c e th e h e x a -
h y d r a t e o f m agnesium c h l o r i d e i s n o t s t a b l e , t h e e q u i v a l e n t s
o f m agnesium p r e s e n t w e re d e te r m in e d by t h e p r e c i p i t a t i o n o f
m agnesium ammonium p h o s p h a te and i t s i g n i t i o n t o t h e p y r o
p h o s p h a te . D u p l i c a t e 100 m l a l i q u o t s w e re e v a p o r a t e d down t o
a p p r o x im a te ly 20 m l; 3 m l o f a 10 p e r c e n t di-am m onium h y d ro
g e n p h o s p h a te s o l u t i o n w ere a d d e d t o e a c h p o r t i o n . D i l u t e
ammonium h y d r o x id e w as a d d ed u n t i l t h e s o l u t i o n s m e lle d d i s
t i n c t l y o r am m onia. T hen3 m l , o f c o n c e n t r a t e d ammonium
h y d r o x id e w e re a d d e d , s i n c e t h e p r e c i p i t a t e i s l e a s t s o l u b l e
i n a s o l u t i o n c o n t a i n i n g one t e n t h i t s volum e o f c o n c e n t r a t e d
ammonium h y d r o x id e . The m i x t u r e s w ere a llo w e d t o s t a n d o v e r
n i g h t . The m agnesium ammonium p h o s p h a te was f i l t e r e d o f f and
w a sh e d , th e n i g n i t e d t o a c o n s t a n t w e i g h t. The r e s u l t s w e re :
6
Sam ple
I •
I I
Wt • o f MggPgOy
0 .1 9 2 1 .grams
0 .1 8 9 4 gram s
T h is d a t a show ed t h e m agnesium s o l u t i o n t o be 0 .0 3 4 1
n o rm a l. 598 m l o f t h i s s o l u t i o n was d i l u t e d t o 1 l i t e r ,
t h u s g i v i n g a s o l u t i o n 0 .0 2 0 4 n o rm a l i n m agnesium c h l o r i d e .
P r e p a r a t i o n o f t h e s t a n d a r d s t r o n t i u m s o l u t i o n : 0 .7 5 4 0
gram s s t r o n t i u m c a r b o n a te w e re d i s s o l v e d w i t h h y d r o c h l o r i c
a c i d . The s o l u t i o n w as e v a p o r a t e d t o d r y n e s s a n d th e n th e
s t r o n t i u m c h l o r i d e w as d i s s o l v e d an d t h e s o l u t i o n made up t o
500 m l. T h is s o l u t i o n w as 0 .0 2 0 4 n o rm a l as. c a l c u l a t e d from
th e w e ig h t o f c a r b o n a t e .
P r e p a r a t i o n o f t h e s t a n d a r d b a riu m s o l u t i o n : 1 .3 3 3
gram s o f b a riu m n i t r a t e w e re d i s s o l v e d i n d i s t i l l e d w a t e r an d
t h e s o l u t i o n w as made up t o 500 m l. As c a l c u l a t e d fro m t h e
w e ig h t t a k e n , t h i s s o l u t i o n w as 0 .0 2 0 4 n o rm a l.
P r e p a r a t i o n o f t a r t r a t e s o l u t i o n : 100 gram s R o c h e lle
s a l t and 6 gram s o f p o ta s s iu m h y d r o x id e w ere d i s s o l v e d i n 500
m l o f d i s t i l l e d w a t e r . 3 m l a r e u s e d f o r a d e t e r m i n a t i o n .
P r e p a r a t i o n o f a l k a l i n e b u f f e r : 10 gram s o f ammonium
c h l o r i d e and 35 m l o f c o n c e n t r a t e d ammonium h y d r o x id e w ere
made up t o 500 m l w i t h d i s t i l l e d w a t e r . 3 m l a r e u s e d f o r a
d e t e r m i n a t i o n .
METHOD OF TITRATING
7
The num ber o f e q u i v a l e n t s o f t h e d e s i r e d s a l t s w ere
o b t a i n e d by m e a s u r in g o u t v o lu m es w i t h p i p e t t e s . A 100 m l
o i l sam p le b o t t l e made a c o n v e n ie n t c o n t a i n e r i n w h ic h t o
e f f e c t t h e t i t r a t i o n . The ammonia o r t a r t r a t e w as a d d ed and
t h e s o l u t i o n made up t o 50 m l. The s t a n d a r d s o a p s o l u t i o n
w as th e n r u n i n fro m a b u r e t t e a n d t h e end p o i n t d e te r m in e d
when t h e s l i g h t e x c e s s o f so a p s o l u t i o n f i r s t c a u s e s a p erm a
n e n t l a t h e r t o p e r s i s t a f t e r s h a k i n g . The m agnesium r e a c t s
l e s s r a p i d l y t h a n t h e c a lc iu m w i t h t h e so a p and s h o u ld be
s h a k e n w e l l a s e a c h s m a ll p o r t i o n o f s o a p i s a d d e d .
BLANK DETERMINATION
3 m l ammonium h y d r o x id e s o l u t i o n made up t o 50 m l.
T r i a l Volume o f so a p r e q u i r e d
1 0 .0 6 m l
2 0 .0 4 "
3 0 .0 6 "
3 m l o f t a r t r a t e s o l u t i o n made up t o 50 m l.
T r i a l Volume o f so a p r e q u i r e d
1 0 .0 6 m l
2 0 .0 7 "
3 0 .0 7 "
From t h e ab o v e d a t a i t i s e v i d e n t t h a t 0 .0 6 m l i s t o
be s u b t r a c t e d fro m t h e o r d i n a r y d e t e r m i n a t i o n s , and when t h e
t a r t r a t e i s a d d e d , t h e n 0 .0 7 m l i s t o he s u b t r a c t e d fro m t h e
am ount o f so a p consum ed f o r a 50 m l sa m p le .
TITRATION o f t h e so a p s o l u t i o n a g a i n s t v a r y i n g am o u n ts o f
c a lc iu m ; w i t h a n d w i t h o u t t a r t r a t e .
TABLE I
M i l l i e q u i v a l e n t s Volume o f so a p s o l u t i o n
T r i a l Qf c a lc iu m (W ith o u t t a r t r a t e ) (W ith t a r t r a t e )
1 0 .1 0 2 3 .6 8 ml 3 .3 6 ml
s 0 .1 0 2 3 .7 5 ’» 3 .3 4 V
3 0 .1 0 2 3 .7 2 » 3 .3 8 "
A v e ra g e 0 .1 0 2 3 .7 1 " 3 .3 6 "
1 0 .2 0 4 7 .0 3 » 6 .7 3 "
2 0 .2 0 4 7 .0 3 " 6 .6 6 "
3 0 .2 0 4 - 7 .1 1 " 6 .7 1 "
A v e ra g e 0 .2 0 4 7 .0 6 " 6 .7 0 "
1 0 .3 0 6 1 0 .3 1 » 9 .9 1 "
2 0 .3 0 6 1 0 .3 6 " 9 .5 0 "
3 0 .3 0 6 1 0 .4 1 " 9 .6 5 "
A v e ra g e 0 .3 0 6 1 0 .3 6 " 9 .6 9 »
The d a t a i n T a b le I shows t h a t t h e c a lc iu m i o n s do n o t
w h o lly e s c a p e from fo rm in g com plex io n s w ith t h e t a r t r a t e
r a d i c a l . So s h o u ld t h e s o a p s o l u t i o n be s t a n d a r d i z e d a g a i n s t
a known am ount o f c a lc iu m i n t h e a b s e n c e o f t h e t a r t r a t e , and
t h e n u s e d t o t i t r a t e a m ix tu r e o f c a lc iu m and m agnesium i n
t h e p resen c e o f t a r t r a t e , a c o n s i d e r a b le , e r r o r may be e x
p e c t e d . The e r r o r w i l l be a n e g a t i v e one i n t h e c a lc iu m
r e p o r t an d be a p o s i t i v e one i n t h e m agnesium r e p o r t .
TITRATION o f t h e so a p s o l u t i o n a g a i n s t v a r y i n g a m o u n ts o f
m ag n esiu m .
: TABLE I I
T r i a l M i l l i e q u i v a l e n t s Volume o f soap
o f m agnesium s o l u t i o n r e q u i r e d
1 0 .1 0 2 4 .5 8 m l
2 0 .1 0 2 4 .6 2 "
3 0 .1 0 2 4 .6 2 "
A v e ra g e 0 .1 0 2 4 .6 1 "
1 0 .2 0 4 7 .1 5 »
2 0 .2 0 4 7 .3 4 "
3 0 .2 0 4 7 .2 8 "
A v e rag e 0 .2 0 4 7 .2 8 ”
1 0 .3 0 6 8 .7 0 »
2 0 .3 0 6 8 .3 3 "
3 0 .3 0 6 8 .6 3 "
A v e ra g e 0 .3 0 6 8 .5 5 ”
The d a t a o f T a b le I I show s t h e m agnesium t i t r a t i o n t o
b e m ore e r r a t i c th a n t h e c o r r e s p o n d i n g t i t r a t i o n o f t h e c a l
cium s o l u t i o n s . Beyond a c e r t a i n c o n c e n t r a t i o n t h e m agnesium
consum ed l e s s so a p s o l u t i o n t h a n a c a lc iu m s o l u t i o n o f t h e
sam e num ber o f e q u i v a l e n t s d i d . B elow t h i s c o n c e n t r a t i o n t h e
m agnesium consum ed m ore so a p s o l u t i o n t h a n d i d t h e c a lc iu m
s o l u t i o n w i t h t h e same num ber o f e q u i v a l e n t s .
The g ra p h on p ag e 10 shows t h e r e l a t i o n o f t h e - d a t a i n
T a b l e s I and I I . A i s t h e c u rv e o f c a lc iu m t i t r a t e d w i t h o u t
t h e t a r t r a t e , an d B i s t h e c u rv e f o r t h e c a lc iu m t i t r a t i o n
w i t h t a r t r a t e p r e s e n t . C i s t h e c u rv e f o r t h e t i t r a t i o n o f
m agnesium w i t h t h e so a p s o l u t i o n .
The d a t a f o r t h e lo w e r p a r t o f c u rv e A h a s b e e n
a c c u r a t e l y d e t e r m i n e d .4 I f th e am o u n ts o f c a lc iu m com plex
4 S ta n d a r d M ethods o f C h e m ic a l A n a l y s i s , by S c o t t ,
V o l. I I , 1 43 9.
(10)
/o
0 3
Curve A is the calcium titration
C u rv e B i s t h e c a lc iu m t i t r a t i o n w i t h t a r t r a t e p r e s e n t
C u rse c i s t h e m agnesium t i t r a t i o n
11
fo rm ed v a r i e d a s th e c a lc iu m c o n c e n t r a t i o n , i t w ould be
* p o s s i b l e t o m o d ify t h e d a t a and u s e i t f o r t h e t i t r a t i o n
b o t h w i t h an d w i t h o u t t h e t a r t r a t e and e l i m i n a t e t h i s e r r o r .
H ow ever, t h i s i s n o t f e a s i b l e .
C urve C i n d i c a t e d t h a t when t h e sa m p le c o n ta in e d l e s s
t h a n 0 .E 1 5 m i l l i e q u i v a l e n t s o f m agnesium , i t consum ed m ore
s o a p t h a n t h e same num ber o f e q u i v a l e n t s o f c a lc iu m d i d ; and
a b o v e 0 .S 1 5 m i l l i e q u i v a l e n t s i t consum ed l e s s . T h is f a c t
s h o u ld n o t b e o v e r lo o k e d , an d when t h e m agnesium i s t i t r a t e d ,
a c o n v e r s io n f a c t o r s h o u ld be o b t a i n e d from su c h a g r a p h a s
a p p e a r s on pag e 10.
I t w as e v i d e n t t h a t a s t h e m i l l i e q u i v a l e n t s o f th e io n s
w ere l e s s , t h e c o r r e s p o n d in g c u r v e s m ore n e a r l y a p p ro a c h e d a
s t r a i g h t l i n e . When t h e s o l u t i o n s .r e q u i r e d l e s s t h a n 5 m l o f
so a p s o l u t i o n , one c o n v e r s i o n f a c t o r c o u ld b e u s e d f o r a l l o f
t h e c o n c e n t r a t i o n s an d y e t b e w i t h i n t h e a c c u r a c y t h i s m ethod
a s a w h o le y i e l d s .
A n o th e r r e a s o n f o r d i l u t i n g t h e s a m p le s s o a s n o t t o
consum e m ore t h a n 5 m l o f so a p s o l u t i o n w as t h a t t h e end
p o i n t becom es p r o g r e s s i v e l y m ore d i f f i c u l t t o d e te r m in e a s
m ore o f th e i n s o l u b l e c a lc iu m an d m agnesium s o a p s a r e form ed
a n d i n t e r f e r e w i t h t h e l a t h e r f o r m a t io n .
The m agnesium com plex f o r m a tio n may b e c o n s i d e r e d
c o m p le te , a s shown fro m t h e f o llo w in g d a t a :
12
T r i a l S o l u t i o n t i t r a t e d °** s o ®P
s o l u t i o n r e q u i r e d
1 3 m l t a r t r a t e , made
up t o 50 m l 0 .0 6 m l
2 " 0 .0 8 "
3 " 0 .0 8 "
1 3 m l t a r t r a t e , 0 .2 0 4
m i l l i e q u i v . Mg,
d i l u t e t o 50 ml 0 .0 8 ”
2 " 0 .0 7 "
3 ” 0 .0 8 » »
ACCURACY DETERMINATIONS
W ith a l l o f t h e e r r o r s i n m ind and w i t h a n a tt e m p t t o
c o r r e c t th em , t h e f o l lo w in g d e t e r m i n a t i o n s w ere made t o c h ec k
t h e g r e a t e s t a c c u r a c y a v a i l a b l e fro m t h i s m eth o d .
The f o l l o w i n g sa m p le s t i t r a t e d c o n ta in e d :
0 .1 0 2 m i l l i e q u i v a l e n t s o f c a lc iu m
0 .0 8 9 m i l l i e q u i v a l e n t s o f m agnesium
W ith t h e t a r t r a t e Volume o f so a p
T r i a l s o l u t i o n r e q u i r e d
1 3 . 2 9 m l
2 3 .4 4 ”
3 3 .3 2 ”
A v e ra g e 3 .3 5 n
W ith o u t t h e t a r t r a t e
1 7 .5 0 m l
2 7 .1 8 ”
3 7 .2 9 »
A v e ra g e 7 .3 2 "
The a v e r a g e volum e o f so a p s o l u t i o n r e q u i r e d f o r t h e
0 .1 0 2 m i l l i e q u i v a l e n t s o f c a lc iu m p r e s e n t was 3 .3 5 ml w h ic h
13
fro m t h e s t a n d a r d i z a t i o n was e q u a l t o 0 .1 0 1 m i l l i e q u i v a l e n t s
o f c a lc iu m . T h is p r o c e d u r e g a v e an e r r o r o f a p p r o x im a te ly
1 p e r c e n t . f o r t h e d e t e r m i n a t i o n f o r c a lc iu m .
The a v e r a g e volum e o f so a p s o l u t i o n r e q u i r e d f o r t h e
0 .0 8 9 m i l l i e q u i v a l e n t s o f m agnesium w as o b t a i n e d by s u b t r a c t
in g 3 .3 5 m l from t h e 7 .3 2 m l, g i v i n g 3 .9 7 m l. From c u rv e C
on p a g e 1 0 , t h i s volum e i s e q u a l t o 0 .0 8 1 m i l l i e q u i v a l e n t s
o f m ag n esiu m . T h is m ethod g a v e a 9 p e r c e n t e r r o r f o r t h e
m agnesium d e t e r m i n a t i o n .
A s u p p o s e d ly unknown sa m p le o f c a lc iu m s a l t , c o n t a i n i n g
0 .1 9 2 5 gram s o f c a lc iu m c a r b o n a t e , w as t a k e n f o r a n a l y s i s and
t h e p e r c e n t a g e o f c a lc iu m i n t h e sa m p le d e te r m in e d . The s o - ,
l u t i o n i n h y d r o c h l o r i c a c i d was e v a p o r a te d t o d r y n e s s and t h e
s a l t s w e re d i s s o l v e d . The s o l u t i o n w as made up t o 500 m l. I n
o r d e r t o f i n d t h e a p p ro x im a te c o n c e n t r a t i o n o f t h e c a lc iu m
■ io n s, 0 .5 0 m l o f t h e s o l u t i o n w as t a k e n f o r a n a l y s i s , and i t
w as fo u n d t o t a k e 0 .2 0 m l o f t h e s t a n d a r d so a p s o l u t i o n .
The sa m p le w as th e n r e g u l a t e d t o consume a p p r o x im a te ly
2 m l o f so a p s o l u t i o n , s o 5 m l sa m p le s w e re p i p e t t e d f o r t h e
d e t e r m i n a t i o n . The r e s u l t s w e re :
Volume o f c a lc iu m s o l u t i o n Volume o f so a p s o l u t i o n
5 .0 0 1 .3 8 m l
5 .0 0 1 .3 5 m l
On c a l c u l a t i n g t h e w e ig h t i n te rm s o f c a lc iu m c a r b o n a t e
a r e s u l t o f 0 .1 8 8 gram s w as o b t a i n e d . T h is g av e a n e r r o r o f
a p p r o x im a te ly 2 p e r c e n t .
summary and c o n c l u sio n s
The o r i g i n a l m ethod o f d e te r m i n i n g t h e h a r d n e s s o f
w a t e r by t h e s o a p t i t r a t i o n m ethod w as p u b l i s h e d by D r. T.
C la r k i n 1 8 4 7 . T h is o r i g i n a l m ethod m e a s u re s t h e t o t a l h a r d
n e s s , t h o s e i o n s p r e s e n t w h ic h form i n s o l u b l e s a l t s o f th e
h i g h e r f a t t y a c i d s . T h is h a r d n e s s i s u s u a l l y due t o c a lc iu m
an d m agnesium i o n s .
A m o d i f i c a t i o n o f t h i s o r i g i n a l m ethod i s one w h ere a n
e x c e s s o f t a r t r a t e i o n i s ad ded t o fo rm a com plex i o n w ith
t h e m agnesium i o n s , t h e n t h e c a lc iu m i s t i t r a t e d t o a n end
p o i n t . W ith o u t t a r t r a t e p r e s e n t b o th c a lc iu m a n d m agnesium
a r e t i t r a t e d , and t h e m agnesium p r e s e n t i s d e te r m in e d by t h e
d i f f e r e n c e i n volum e o f t h e s t a n d a r d so a p s o l u t i o n r e q u i r e d
f o r t h e two t i t r a t i o n s . T h is v o l u m e t r i c d e t e r m i n a t i o n o f c a l
cium a n d m agnesium i s r a p i d a s com pared t o t h e g r a v i m e t r i c
d e t e r m i n a t i o n s o f c a lc iu m and m agnesium .
On r e a d i n g t h e l i t e r a t u r e t h e r e seem ed t o be c o n f l i c t
o f o p i n i o n i n r e g a r d t o t h e a c c u ra c y t h e so a p t i t r a t i o n was
c a p a b le o f p r o d u c in g , so t h e p u r p o s e o f t h i s s tu d y w as t o
c o l l a b o r a t e d a t a on t h e v a r i o u s f a c t o r s w h ic h w ould i n f l u e n c e
t h e t i t r a t i o n , e l i m i n a t e t h e s e s o u r c e s o f e r r o r a s w e l l a s
p o s s i b l e , an d c h ec k t h e a c c u r a c y o b t a i n e d by t i t r a t i n g known
a m o u n ts o f c a lc iu m and m agnesium . I f t h e a c c u r a c y p e r m i t t e d ,
t h e n t h e m ethod w ould b e a d a p te d t o r o c k a n a l y s i s f o r t h e
d e t e r m i n a t i o n o f s m a ll am o u n ts o f t h e s e l a t t e r i o n s .
15
The am ount o f i n s o l u b l e c a lc iu m and m agnesium s o a p s
p r e s e n t a t th e tim e t h e end p o i n t i s a t t a i n e d a f f e c t s t h e
r e s u l t s . I t c a u s e s a p o s i t i v e e r r o r , an d t h e s e c o n c e n t r a
t i o n s s h o u ld be m in im iz e d by d i l u t i n g t h e sa m p le so t h a t
s m a ll am o u n ts o f so a p s o l u t i o n a r e r e q u i r e d .
The t e m p e r a t u r e o f t h e s o l u t i o n a f f e c t s t h e am o u n ts
o f so a p s o l u t i o n n e e d e d t o form a l a t h e r . C o n s e q u e n tly , t h e
s o l u t i o n s t i t r a t e d s h o u ld be u n if o rm i n t e m p e r a t u r e . A d e
c r e a s e o f t e m p e r a t u r e c a u s e s a n i n c r e a s e i n t h e volum e o f
so a p r e q u i r e d .
The f r e e c a rb o n d i o x i d e an d a c i d i t y i s a f a c t o r w h ic h
a f f e c t s t h e t i t r a t i o n , an d i s e l i m i n a t e d b y r e n d e r i n g th e
s o l u t i o n s b a s i c b e f o r e t i t r a t i n g w i t h t h e s t a n d a r d so a p
s o l u t i o n .
The volum e o f so a p s o l u t i o n r e q u i r e d f o r a d e f i n i t e
num ber o f e q u i v a l e n t s o f c a lc iu m i o n s i s n o t t h e same a s t h e
volum e r e q u i r e d f o r th e same c o n c e n t r a t i o n o f m agnesium i o n s .
The r e l a t i o n b e tw e e n t h e tw o s h o u ld be g ra p h e d and a c o n v e r
s i o n f a c t o r o b t a i n e d from t h e g r a p h .
C a lc iu m io n s do n o t w h o lly e s c a p e from fo rm in g com plex
io n s w i t h t h e t a r t r a t e , and t h e e x t e n t o f f o r m a tio n may be
g ra p h e d and c o n v e r s i o n s o b t a i n e d fro m i t .
A f t e r th e p r e c e d i n g f a c t o r s w e re m in im iz e d , a n a v e r a g e
e r r o r o f 5 p e r c e n t w as o b t a i n e d . The c a lc iu m e r r o r s w ere
u s u a l l y l e s s a n d th e .m a g n e s iu m e r r o r s g r e a t e r .
16
B ariu m an d s t r o n t i u m r e a c t e d v e r y much t o t h e same
e x t e n t a s d id t h e c a lc iu m . I f t h i s t i t r a t i o n i s t o be u s e d
i n r o c k a n a l y s i s , t h e n t h e c a lc iu m a n d m agnesium io n s m ust
be i s o l a t e d fro m o t h e r b i v a l e n t and t r i v a l e n t i o n s .
BIBLIOGRAPHY
BIBLIOGRAPHY
A. P . H. A. , S ta n d a r d M ethods f o r t h e E x a m in a tio n o f W a te r
and S ew age, E ig h th e d i t i o n , 1 9 3 6 , 59 .
C l a r k , J . , The E x a m in a tio n o f W a te r f o r Towns f o r I t s H a rd
n e s s a n d f o r t h e I n c r u s t a t i o n s i t D e p o s i t s , Chem. G a z .,
5100 ( 1 8 4 7 ).
K ean , R. H . , and H. G u s ta f s o n , Some F a c t o r s I n f l u e n c i n g Soap
T e s t s f o r H a r d n e s s , I n d . a n d E n g r . C hem ., A n a l y t i c a l
e d i t i o n , V o l. 3 , 3 5 5 -3 5 6 , 1 9 3 1 .
S c o t t , W ., S ta n d a r d M ethods o f C h e m ic a l A n a l y s i s , F o u r th
e d i t i o n , V o l. I I , 1 439 .

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Asset Metadata

Creator Ball, E. J (author)

Core Title A critical study of the application of the soap titration method to the determination of calcium and magnesium

Degree Master of Arts

Degree Program Chemistry

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag chemistry, inorganic,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor [illegible] (committee chair), [illegible] (committee member), Roberts, L.D. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c17-788123

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Legacy Identifier EP41513.pdf

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Document Type Thesis

Rights Ball, E. J.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

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