La perspectiva de la justificación en la “Carta a los romanos”

8 . 2 APPLICAT I ON

In order to apply the I o� Exchange M e thod the

hypothe t i cal exp eri m ent d e s crib ed ab ov e mu st b e repl a c ed b y an e�uiv al ent set of exp er i m e nt s . The s e a r e :

( 1 ) From a s e ri e s of e�ui lib rat i ons of b e ad s of i on exchange r e s i n wi t h different s t andard solut ions find emp i ri cal relati onship s b etween r e s i n compos i t ion and activi t y �uot i ent s .

( 2 ) E�ui l i brat e an e xc e s s of the unknovm solut i on wi th i on exchange resin and d e t ermine r e s i n composi t ion.

( 3 ) U s e the emp i ri cal re l a t i onship s and the e �u i libri um re s i n comp o s i t ion to cal culat e th e activi ty �uot i ent s for th e unknown solut i on .

The s e exp er i ment s are now di scu s s ed in more d e t ai l .

1 . R e s i n C ali brati on

Activ i t y �uoti ent s fo r d i lu t e a�ueou s solut i ons of s t rong e l e c t rolyt e s of known comp o s i t i on can b e cal culat ed u s i ng the D ebye-Huckel e�ua t i on for activi ty c o e ffi c i ent s :

l og 'Y i =

-A zi

2 ..J

I 1 +

Ba1

.

..J

I

whe r e the s ymb ol s have thei r u s ual me anings . V alue s of the clo s e s t approach p arame t er , a i for vari ous c a t i ons h av e b e en given b y Ki e lland ( 1 937 ) . For thi s r e a s on such

soluti ons ar e u s e ful for ' c alib rating ' the i on e xchange

re s i n . A s eri e s of such solu t i on s ar e e�ui libra t ed wi th di ffe r ent port i ons of i on e xchange re s i n aft er whi ch

solut i on and r e s i n are sep ar a t e d and are analysed.

Funct i onal relat i onship s b et w e e n a c t ivi ty q_uoti ent s and

r e s i n comp o s i t i on are then found emp i ri call y . I t i s no t

nec e s s ary fo r the calibra t i ng s olut i ons all to hav e the

same i oni c s t r ength al though i oni c s trength mus t b e suffi ci ently low for th e Debye-Huckel equat i on t o apply.

2 . UYL"known S olut i o:-1 b ra t i on

A large volume of the solu t i on under i nv e s t i ga t i on i s e quilibrat ed wi th a small port i on of i on exchange res i n .

B e cau s e t h e s olut i on i s pre s ent i n exc e s s i t s comp o s i ti on

i s not s ensibly alt e red b y the e qui l i b rat i on . Aft er the

equi l ib rat i on the resin ha s a c o mpos i t ion whi ch i s

charact eri s t i c of the acti vi ty quot i ent s of the solu t i on .

3 . C al c ulat i on o :f the Quoti ent s for the Unkno-vVn Solut i on

---

The activi ty q_uot i ent s for t h e s olution under i nv e s t- i gat i on are found by sub st i tuti ng t he equilibri um r e s i n comp o s i t i on i nto the emp i ri cal relati onshi p s for the acti v i t y quot i ent s .

A DISC U S S I ON OF THE WOHK OF VAN KREVELD

Ai'IJD VA.TI{ MINNEN 1

The cati on exchange r e s i n method for det ermini ng

cat i on a ct ivi ty quo t i ent s ha s b een app l i ed t o milk s ev eral t ime s

(

s e e Chap t er 7 ) s i nc e i t s i ntroduct i on b y

Chri s t i an s e n , J enne s s and C oul t e r in 1 952 and has r e c ently b een app li ed to the int e s t inal c ont ent s of ruminan t s

(

M olloy and Ri chard s , 1 97 1 ) . Th e theory b ehi nd the

me thod d o e s not appear to have b e e n d i scus s ed i n the

li t erature and there seems t o hav e been li t tl e appre c i at i on of the gene rali t y of the method. I t has b een shown i n

C hap t e r

8

that the cat i on exchange re sin method g i ve s

cation a c t i vi ty quot i ent s . The p robl em re mai ns of

e st i mat i ng s ingl e cat i on a c t ivi t i e s fro� the s e quot ient s. V a n Kreveld and V an M i nnen ( 1 955 ) have di scus sed part s of

thi s p robl em in s ome detai l and a cri ti cal di s cus s i on and ext ens i on of thei r argument s i s given i n thi s C hap t er .

of I on Ac t ivi t i e s

The act ivi t y o f a singl e i on i c speci e s cannot b e det ermined from thermodynami c s tudy alone but requi re s the adop t i on of s om e extrathermodynami c as sump t i on or c onv ent i on . Th e si gni fi cance and meaning of s ingl e i on a c t i vi t i e s i s the sub j ec t of di fferences of op ini on w i t h m any thermodynami c puri s t s cont i nui ng to opp o s e the

In document Justificación, memoria y derechos humanos Marcos y horizontes actuales de fundamentación (página 34-99)