Potentiometric Titration

POTENTIOMETRIC TITRATION I. Introduction Acid-base Acid-base titrations, by concept, is also called a neutralization neutralization reaction, since it involves an acid and a base (tat is re!ardless o" stren!t, eiter one is #ea$ or one is stron! or eiter #ea$ or bot stron! and ad in%nitu&', and re!ularly ave te products o" salt and #ater Te co&pletion o" te reaction is reaced #en te nu&ber o" &oles o" te acid is e)ual to te &oles o" te base, or tecnically te e)uivalence point is reaced In tis point, i" te stoicio&etric ratios o" te acid and base are e)ual, #e can solve "or te concentration o" te un$no#n by usin! te dilution e)uation, e)uation, tat is, M *+*M+ .or diprotic and triprotic acids and bases tat are titrated #it a stron! acid/base, o#ever, ave &any e)uivalence points, dependin! on o# protic it is(ie a diprotic acid/base as t#o e)uivalence points, #ereas a triprotic acid/base as tree' since te acid/base as to converted to its less acidic/basic "or&, "or&, or its inter&ediates A !ood e0a&ple #ould be a diprotic acid titrated usin! a stron! base (in tis case, sodiu& ydro0ide', or 1A Te reaction #ould proceed, "or&in! 1A-, and ulti&ately "or&in! te base, A - 2ut in tis titration, you cannot deter&ine its actual p1 at a certain ali)uot o" te titrant, since #at #e are usin! in tis type o" titration is an indicator, an or!anic co£ co£ added to te solution to see te e)uivalence point by a can!e o" color In doin! so, a p1 &eter is used to &onitor te &easure&ent &easure&ent o" p1 o" te titration process at and Te p1 &eter &easures &easures te 31 45 concentration concentration o" te solution, so i" te titration !oes "ro& base to acid, te p1 &ust be co&puted as p1*6-pO1, #ere pO1 is te initial readin! o" p1 2y usin! a p1 &eter in an acid-base titration to &onitor te p1 variations o" te titration process, process, #e call tis process a potentio&etric titration, #erein it %nds te e)uivalence point not trou! an indicator, but trou! a !rap tat si!ni%es te relationsip bet#een te recorded a&ount o" titrant used, and te &easured p1 o" te syste&

II. Methodology Obtain te un$no#n sa&ple "or your !roup .ro& your laboratory instructor, obtain te &ass o" te un$no#n sa&ple and its &olar concentration Potentionmetric Potentionmetric Titration of Unknown Acid buret #as %lled up to te 77-&8 &ar$ #it te standard 779 N NaO1 Te initial p1 o" te un$no#n acid solution #as recorded Te un$no#n acid solution #as titrated potentio&etrically #it te standard NaO1 solution usin! *97-&8 ali)uots o" titrant at a ti&e :teer te :olution a"ter every titration Te *97-&8 ali)uots o" titrant #as repeated 6 ti&es, ne0t 9&8 ali)uots "or ; ti&es, ten *7&8 ali)uots < ti&es, and lastly 7&l ali)uots "or  ti&es Te p1 level #as recorded a"ter every titration III. Results and and Di Discussion =n$no#n Acid :a&ple Mass o" bea$er Mass o" bea$er 4 acid Mass o" acid Molarity p1 Potention&etric Titration o" =n$no#n Acid  Titrant  Titrant +olu&e, +olu&e, &8 (*9&8 ali)uot' ali)uot' *9 ? 69 <  Titrant  Titrant +olu&e, +olu&e, &8 (9&8 ali)uot' ali)uot' ** *< *

<>6?7! ;;?*>9! 7;;>?! 7M *6

p1 *6 *6 *9 *9 *9 *< *>

< ?* ?< 6* 6<  Titrant +olu&e, &8 (*7&8 ali)uot' 9< << >< ;< @< *7<  Titrant +olu&e, &8 (7&8 ali)uot' *< *6<

*> *; *@ 7 7 6 9 ?* 9; <6 <@ >6 ;

Graph p !s. "olume of titrant

 pH @ ; > < 9 6 ?  * 7 7

7

67

<7

;7

*77

*7

*67

*<7

Titrant Volume, mL 2ased on te !rap #ill be te deter&ination o" te ionization constant  a o" te un$no#n acid Tis #ill co&e in t#o #ays .irst #ould be te calculation o" te ionization constant usin! titration data 2y !ettin! te volu&e o" te titrant at te e)uivalence point, on te al" -e)uivalence point, and te p1 value o" 97B neutralization, #e can co&pute "or te p1 o" te syste& by usin! te e)uation p197B neutral  pa and p1  pa 4(A - / 1A' A"ter tis, te oter &etod #ould be te calculation o" te ionization constant based on initial p  2y avin! te assu&ed concentration o" te un$no#n acid to be e)ual to te concentration o" te titrant and its initial p1, te p1 #ill be co&puted by te "ollo#in! e)uation p1  3145 / (C1A - 3145' 2y co&parin! bot values to so&e $no#n acidDs ionization constants, te identity o" te un$no#n acid #ill be clari%ed

I".

#ummary and conclusion

 Tis e0peri&ent concluded te concepts involvin! potentio&etric titration 2y speci%cally usin! a calibrated p1 &eter usin! buer solutions o" standardized concentrations, te p1 o" te solution is constantly &easured as to addin! an e0act a&ount o" te titrant tat is &easured accordin!ly to its e)uivalent ali)uot Tis is done until te p1 o" te syste& is constant and &ore or less basic (since #e are andlin! an analyte tat is classi%ed as an un$no#n acid, #ic is bein! titrated by a stron! base' A"ter plottin! te values o" p1 a!ainst volu&e o" te titrant, #e "or& a !rap tat #ill deter&ine te e)uivalence point o" te reaction 2y usin! te values o" te volu&e F97B neutralization, te e)uivalence point and te initial value o" te p1, #e can co&pute "or te ionization constant o" te un$no#n acid, as #ell as identi"yin! te &olecular "or&ula o" te acid and identi"yin! te acid itsel" Errors sould be avoided especially on te consistency o" puttin! an e0act a&ount o" te titrant, as tis #ill in s&all a&ounts, #ill collectively deter te position as to #ere te e)uivalence point sould be, tere"ore !ettin! an incorrect ionization constant in te "ollo#in! can!es, and it "urter deteriorates te consistency o" te e0peri&ent itsel"

". References Cristian, Gary H 776 Analytical ce&istry (