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pH Measurement and Bufer Preparation
Dela Rosa, M.L., Diaz, K.I.M, Domingo, M.A., Dungca, M.K.,
Gabayan, M.2H – Pharmacy, acul!y o" Pharmacy
#ni$ersi!y o" %an!o &omas
Abstract
&he e'(erimen! )as *one !o *e!ermine !he elec!rome!ric
(H o" !he bu+ers
an* sam(les )i!h !he use o" !he (H me!er an* !o *i+eren!ia!e
!hem by
colorime!ric *e!ermina!ion me!ho* !hrough using *i+eren!
aci*base
in*ica!ors. &he in*ica!ors use* )ere !hymol blue, )hich is a
*i(ro!ic aci*,
bromo(henol blue, bromocresol green, bromocresol (ur(le, (henol
re*,
me!hyl re*, me!hyl orange, an* (henol(h!halein. &he bu+er
!ha! )as
assigne* !o be ma*e )as an ace!a!e bu+er )i!h a (H o" - )hich
)aschece* by !he (H me!er. &he sam(les use* )ere !he coconu!
/uice an*
*is!ille* )a!er. Dis!ille* )a!er ha* a (H o" - gi$en !ha! one o"
!he columns in
!he (H me!er ma!che* in!o !ha! o" !he *is!ille* )a!er. 0n !he
o!her han*, !he
coconu! /uice )hich ha* a (H o" -.1 )as *e!ermine* by !he (H
me!er by
using !he elec!rome!ric *e!ermina!ion me!ho*.
Introduction
All biological (rocesses are
grea!ly a+ec!e* by (H 3risos!omo
A.3.,e! al.24546. &he !erm (H is
use* !o i*en!i"y !he concen!ra!ion
o" 7H89, !hus !he (H o" a solu!ion is
sim(ly !he nega!i$e logari!hm o"
7H89.
&he (H o" a solu!ion is
grea!ly *e(en*en! on !he
concen!ra!ion o" 7H89 ions, !hus
bu+ers are re:uire* !o main!ain !he(H by bin*ing !he 7H89 ions
)hich
in !urn s!abilizes !he changes in (H.
;3once(!s in
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rela!ionshi( be!)een (H an* !he
(Ka o" a )ea aci*?
&here are !)o me!ho*s in!his e'(erimen! !ha! )ere use*
in
or*er !o *e!ermine !he (H namely
!he Electrometric determination
method an* !he Colorimetric
determination method. &he
elec!rome!ric *e!ermina!ion
me!ho* is !he mos! accura!e o" !he
me!ho*s em(loye* "or !he
*e!ermina!ion o" hy*rogen ion
concen!ra!ion an* !he acce(!e*me!ho* "or research an*
labora!ory
)or necessi!a!ing (H
measuremen!s accura!e !o 4.5 !o
4.445 (H B 46 )hile
!he colorime!ric *e!ermina!ion
me!ho* measures color )herein
chemicals are a**e* !o !he sam(le
an* !hose chemicals reac! )i!hsam(le (ro*uces a color change
;Physical Pro(er!ies? Ca!er
3hemis!ry? (H, "rom Disco$ery o"
s!uarine n$ironmen!s
D06=,n.*., (ara. 56. In !he
colorime!ric *e!ermina!ion me!ho*,
!hese chemicals )ere use* !o
*e!ermine !he (H o" a solu!ion, an*
are calle* aci*base in*ica!ors.
Aci*base in*ica!ors are ei!her)ea organic aci*s, HA, or )ea
organic bases, 4 8 log '6J 4.-4
5.-4 4.54 5
4.4FL 544.4F
4.4
(H (Ka 8 log 7sal!97aci*9
-.44 .>4 8 log J4.1 log JJ 4.-4
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mar. &hen !he con!ainer )as
labele* (ro(erly.
Ace!a!e
lec!rome!ric De!ermina!ion o" (H
&he (H me!er )as calibra!e*
!o - an* )as measure* using 24
mL (or!ion o" bu+er solu!ions,
*is!ille* )a!er an* coconu! /uice.
&he 7H89 o" !he sam(le use* )as
calcula!e*. &he (H o" !he bu+ersolu!ion )as a*/us!e* !o
!he
*esire* (H by a**ing 5.4 M H3l or
5.4 M a0H in (or!ion )hile
being moni!ore* by !he (H
me!er.
3alorime!ric De!ermina!ion o" (H
A. Pre(ara!ion o" color
s!an*ar*s using !he bu+ersolu!ions?
%i' !es! !ubes )as (re(are* an*
labele* )i!h !he (H o" !he bu+er
an* aci*base in*ica!or !o be
a**e*. - mL o" !he bu+er )as
(lace* in each !es! !ube an* 2
*ro(s o" an aci*base in*ica!or )as
a**e*. &he mi'!ure )as shaen
an* !he resul!ing color )as no!e*. &he (roce*ure )as
re(ea!e* using
!he "ollo)ing aci*base in*ica!ors?
Acid-baseindicator
pH Distilled
ater
!ample
"#$ %#$ $ '#$ '#& (#$ )"#$
&hymol blue orange yello) yello) yello) yello)
yello)
blue yello) yello)
mole ' [email protected] @.EFg Ace!a!eaci*6
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&hymol blue,
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bromo(henol blue an* bromocresol
green change* color a! (H -.4
)hile bromocresol (ur(le change*
i!s color a! (H >.4. Me!hyl orange
an* (henol re* bo!h change* !heir
yello) ini!ial color in!o orange bu!
a! *i+eren! (H, (henol re*
*omina!e* orange color "rom (H
>.4 )hile me!hyl orange change*
i!s color a! (H -.4. &hese color
changes !ell !)o !hings. 0ne, i" !he
aci* )as a**e* !o !he solu!ion,
more H8 )as (ro*uce* )hich
resul!e* !o change color o" !he
solu!ion !ha! ma!che* !ha! o" anHIn. 0n !he o!her han*, i"
more
base )as a**e*, more 0H )oul*
be !he resul! causing !he solu!ion
!o change color !ha! )oul* ma!ch
!ha! o" In.
Dis!ille* )a!er )hich ha* a
yello) color resul!s a"!er !he
a**i!ions o" !he !hymol blue an*
(henol re* se(ara!ely, blue color
)as !he resul! in a**i!ions o" bo!h
bromo(henol blue an* bromocresol
green, green color resul!e* )hen
*is!ille* )a!er )as a**e* )i!h
bromocresol (ur(le, orange )as
!he $isible resul! a"!er !he a**i!ions
o" me!hyl re* an* o" me!hyl
orange, an* !hen i! )as colorless
a"!er a**ing )i!h (henolo(h!halein.
&hese colors o" each in*ica!or
ma*e !he *is!ille* )a!er "all in
aroun* (H -.4 since i!s resul!s )ere
$isibly seen a! !he (H -.4 column.
&he sam(le, )hich )as !he
coconu! /uice, "ell in !he (H o"
aroun* -.4. %imilar case )i!h
*is!ille* )a!er, !he sam(les
in*ica!ors ma!che* a! a gi$en (H in
!he !able !ha! ha* yello) color )as
!he resul! a"!er a**i!ions o" !hymol
blue an* me!hyl
re*, (ur(le color )as seen a"!er i!
)as being a**e* )i!h bromo(henol
blue an* bromocresol (ur(le
se(ara!ely, orange color resul!e*
a"!er (henol re* an* me!hyl orange
)ere se(ara!ely a**e* !o i!, a blue
color )as )i!nesse* a"!er a**ing
)i!h bromocresol green, an* a
colorless )as !he resul! )hen i!
)as a**e* )i!h (henolo(h!halein.
3onclusion
De!ermina!ion o" !he (H o" acer!ain subs!ance or solu!ion
!hrough aci*base color in*ica!ors
sho)s !he *i+eren! range o"
$arying colors )hen a color
in*ica!or is a**e* !o a solu!ion )i!h
a cer!ain (H. 3hemical reac!ions
!ha! al!er !he (hysical (ro(er!ies o"
color in*ica!ors are obser$e* )hen
!hese are mi'e* )i!h a (ar!icularly
aci*icbasic solu!ion. 3olor
in*ica!ors are sensi!i$e enough !o
change i!s (hysical color because
o" !he elec!ron connemen!
ha((ening in !he (rocess o"
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agi!a!ing !he !)o li:ui*s. More
connemen! maes !he ligh!
absorb *arer sha*es an* hues,
an* less connemen! maes i!
absorb ligh!er sha*es.
Re"erences?
3risos!omo A.3.,e! al.24546.
Laboratory Manual in General
Biochemistry , Nuezon 3i!y,
Phili((ines.
;3once(!s in
