CHEMISTRY LABORATORY REPORT Experiment 2: pH AND BUFFERS
To: Instructor: PhD Hoang Le Son From: Do Truong Anh Thu - Student ID: BTBCIU14046 Subject: General Chemisr! La"oraor! Date: #$o"er 1% h& %01'
I. INTRODUCTION
This e()erimen )ro*i+es us he meho+ o $onrol or e,uili"rium he s!sem "! he )H *alue I is *er! im)oran .or organisms o mainain a sa"le )H Biologi$al mole$ules su$h as )roeins .un$ion onl! a a $erain )H le*el an+ an! $hanges in )H $an resul in hem no .un$ioning )ro)erl! The $on$enraion o. H/ in he soluion ells ho a$i+i$ or alaline a su"san$e is an+ i is iner)ree+ "! he )H& an+ "u..ers are he soluion o mainain his *alue The srong or ea "ase2a$i+ an+ he neural soluion ha*e +i..eren )H *alue an+ e $an no more a"ou a" ou his as ell as $al$ulaions relae+ o )H *alue& or ho "u..ers $onrol he )H hrough his e()erimen II. PROCEDURE A. Instruments:
Three 1'0 mL "eaers
)H meer
Three %'0 mL "reaers
aer "ah
#ne 10 mL *olumeri$ )i)e
#ne sirring ro+
#ne 10 mL grauae+ )i)e
#ne me+i$ine +ro))er
3agnei$ sirrer an+ sir "ar
B. Procedure: System !: De"on"#ed $ater
e ha*e a"ou 1'0 mL o. +eioni5e+ "oile+ .or 10 minues in a %'0 mL "eaer an+ hen $oole+ o room em)eraure
The ne( se) is o )our a"ou ' mL o. he room em)eraure aer ino a 1'0 mL "eaer Then e a++ a sir "ar o he "eaer an+ )la$e he "eaer on a magnei$ "ar sirrer Assem"le )H meer
e re$or+ he )H *alue an+ hen sirl he aer ih he magnei$ sirrer .or a"ou %0 se$on+s 7e$or+ he )H again an+ re)ea he sirring an+ measuremen )ro$ess a %0 se$on+ iner*als& re$or+ing ea$h ime an+ )H *alue& unil here is no a))re$ia"le $hange in he )H System %: Stron& ac"d
3easure he )H "! using )i)e o ae 10 mL o. 01 3 HCl ino a %'0 mL "eaer
3easure he )H a.er a++ 80 mL o. +isille+ aer ino he "eaer 3easure he )H
10 mL o. 010 3 9a#H as a++e+ ino he "eaer 7e$or+ he )H
80 mL o. 001 3 9a#H as a++e+ ino he "eaer 7e$or+ he )H System ': (ea) ac"d
%0 mL o. 01 3 a$ei$ a$i+ as )la$e+ )la$ e+ ino 1'0 mL "eaer
Using 01 3 a$ei$ a$i+ as a saring )oin& mae hree +iluions resuling in o +i..eren $on$enraions& iie 001 an+ 0001 3
3easure he )H o. ea$h hese soluion an+ $al$ulae he a .or ea$h o. he soluions System *: Sa+ts
'0 mL o. 01 3 9aCl as )la$e+ ino a 1'0 mL "eaer 3easure he )H
Pla$e '0 mL o. 001 3 CH;C##H ino a 1'0 mL "eaer 3easure he )H
Pla$e '0 mL o. 01 3 9H4Cl ino a 1'0 mL "eaer 3easure he )H
System ,: Bu--ers
100 mL ea$h o. 01 3 CH;C##H an+ 01 3 CH;C##9a ere )la$e+ ino se)erae 1'0mL "eaer
Pre)are "u..er A& B& C "! mi(ing hese o soluions as shon in he a"le "elo 3easure he )H o. he "u..er soluion Di*i+e ea$h o. he ; "u..ers ino e,ual )ars <%'0 mL ea$h=
•
Par 1: >or one sam)le o. ea$h "u..er: "u..er:
-
A++ 10 +ro)s o. 01 3 HCl 3easure he )H
-
A++ enough o $hange he )H "! one uni .rom he sar 7e$or+ he *olume
Par %: >or one sam)le o. ea$h "u..er: "u..er:
-
A++ 10 +ro)s o. 01 3 9a#H 3easure he )H
-
A++ enough o $hange he )H "! one uni .rom e sar 7e$or+ he *olume
III. DATA AND DISCUSSION !. / OF DEIONI0ED (ATER T"me 1s2
Obser3ed /
E4+anat"on
5
8.'7
%5
8.%,
*5
8.!8
65
8.!'
75
8.!5
!55
8.5*
The +eioni5e+ aer in he la"oraor! room has a )H *alue a))ro(imael! 0 The )ro$ess o. +isillaion lea+s aer mole$ules o a$$ess he air $onaine+ C#% gas an+ sirring en$ourage more an+ more C#% +issol*e+& so he $on$enraion o. a$i+ in +isille+ aer a ha ime in$reases an+ he )H *alue +e$reases as a resul A.er a shor )erio+ o. ime& +ue o he aer +oes no a"sor" all o. C#% .rom he air& he "alan$e sage ha))ens an+ he )H *alue is sa"le
Comment: The )H o. +eioni5e+ aer en+s o "e loer han normal aer "e$ause he +issol*e+ sals
So+ut"on
Teoret"ca+ /
;easured /
E4+a"nat"on
?10 mL o. 013 HCl
1
-;1@
%
0%
084
HCl is srong a$i+ so is )H *alue is small as he H/ 01 in*ol*e+ in hen a++ing he +isille+ aer ino HCl& he soluion "e$omes +ilue+ an+ he $on$enraion o. H/ +e$reases The s!sem has he $urren H/ 001& hus he )H *alue $al$ulae+ e,ual o %
11
1'4
? A++ 80 mL o. +isille+ aer ? A++ 10 mL o. 013 9a#H ? A++ 80 mL o. 0013 9a#H
The )H *alue ee)s in$reasing +ue o he a++iion o. 9a#H& #H- +issol*es an+ oins ih H/ in he mi(ure o mae H%# Thus he s!sem is neural an+ he )H raise ino hen e $oninue o a++ 80mL o. 001 9a#H o he mi(ure& he #H- in$rease an+ e,ual o %; so he )H *alue raise heorei$all! o 11
Data Ca+cu+at"on:
The mole o. 10mL o. 0&1 3 HCL: n C3 ( E 0&1( 001 10-;
The $urren #H- n2E 8(10-42018 Thus he .inal )H 14 - <-log 8(10-42018= 11 Comment: The )H *alue +e)en+s on $on$enraion o. H/ Srong a$i+ o.en ha*e a small )H *alue "e$ause he i +issol*es $om)leel! in aer o )ro+u$e he large amoun o. H/ The )H o. srong a$i+ ill "e in$rease hen #H- is in$rease+ The reali! *alue o. )H in he e()erimen e()e rimen is +i..eren $om)aring ih he heorei$al one +ue o he la"oraor! $on+iions an+ he misae +uring e()erimenal )ro$e+ure Note: The resuls in his e()erimen are rong "e$ause he )H meer is rong& m! grou) rie+ o measure )H o. 9a#H an+ HCl man! man ! imes "u i is no righ '. / OF (EA< ACID So+ut"on
;easured /
E4+a"nat"on
013 a$ei$ a$i+
% 4 4
1;6(10-4
0013 a$ei$ a$i+
; 0 4
81'(10-'
00013 a$ei$ a$i+
; 6 6
61%(10-'
CH;C##H )la!s role as he *er! ea a$i+& resuls in +issol*ing )ariall! an+ .orming lile H/& hi$h lea+s o he )H *alue is higher han he srong a$i+ The less $on$enraion o. H/ in he a$ei$ a$i+ soluion& he more in$reasing in he )H *alue
Data Ca+cu+at"on:
Deermining he a "ase on he measure+ )H o.: >irs& 01 3 a$i+ a$ei$ CH;C##H Iniial
F
H/ /
CH;C##-
01
0
0
Change
(
(
(
,uili"rium
01-(
(
(
Thus he a
AH +BACH;C## B
(%
ACH;C##HB
0-1 − x
<10-%44=%2 <01 - 10-%44= 1;6(10-4
Se$on+& 001 3 a$i+ a$ei$ an+ a))l!ing he same e,uaion a"o*e AH+BACH;C## B ACH;C##HB
<10-;04=% 2 <001- 10-;04= 81'(10-'
Thus he a
Thir+& 0001 3 a$i+ a$ei$ an+ a))l!ing he same e,uaion a"o*e AH +BACH;C## B ACH;C##HB
<10-;66=%2 <0001- 10-;66= 61%(10-'
Thus he a *. / o- SA=TS: So+ut"on
Pred"cted /
;easured /
E4+a"nat"on
013 9aCl
8
64 64
013 CH;C##9a
>8
8;
9aCl is is a sal o. o. s srong a$ a$i+
013 9H4Cl
?8
'@
CH;C##9a is he sal o. a ea a$i+ a$ i+
Comment:
The )H o. he sals +e)en+ on he $om)oun+ o. ha su"san$e& i. he $om)oun+ is he srong non-meal su$h as 9a an+ he ea a$i+ $om)onen su$h as CH;C##-& he )H is o*er & on he $onrar!& he he )H is less han & an+ i. % $om)onens are srong a$i+2"ase& he soluion "e$omes neural
,. / o- BUFFERS:
Bu--er -er
@o+ume +ume 1m=2 m=2 5.!; C/'COO/
@o+ume 1m=2 5.!; C/'COONa
Ac"d
A
1 0 0
400
00%
00@
';4
'%8
B
4 0 0
100
00@
00%
414
;@@
C
% ' 0
%'0
00'
00'
44
4;%
Base
Ca+cu+ated /
;easured /
Data Ca+cu+at"on:
Deermining he A$i+& Base an+ he )H *alue: >or he mi(ure A: CH;C##H CH;C##- / H/ 0001
(
CH;C##9a
( CH;C##- / 9a/
000 0004 4 0-001
n
E
=
0-01 + 0-04
000 0004 4 =
A$i+ CH;C##H
00% 3 n
E
=
0-004 0-01 + 0-04
=
Base CH;C##9a
00@ 3
nCH;C##- 0004 / ( 0004
0-0@ x
ACH;C##HB
0-0%
a
1@ ( 10-'
J ( 4'(10-6 <3= Thus he )H is )H -log( ';4 A))l!ing he same $on$e) .or mi(ure B an+ C
000 0004 4
Part I: Add"t"on o- !5 dros 5.! ; /C+
Bu..er
)H .rom he sar
)H a.er a++ing HCl
Toal *olume HCl o $hange )H "! one uni
A
'%8
'0
;8 mL
B
;@@
;8;
1; mL
C
4;%
410
18 mL
()lanaion
a$h "u..er has he ea "ase CH;C##-& i rea$s ih he a++e+ H/ o. HCl so he )H o. he soluion is no +e$rease oo mu$h hen a++ing 10 +ro)s HCl
Part II: Add"t"on o- !5 dros 5.! ; NaO/
Bu..er
)H .rom he sar
)H a.er a++ing 9a#H
Toal Toal *olume 9a#H o $hange )H "! one uni
A
'%8
';'
10 mL
B
;@@
;8;
%0 mL
C
4;%
4;@
18@ mL
()lanaion
a$h "u..er has he ea a$i+ CH;C##H& i rea$s ih he a++e+ #H- o. 9a#H so he )H o. he soluion is no in$rease oo mu$h hen a++ing 10 +ro)s 9a#H
Comment
Bu..er A ha*e he highes )H *alue "e$ause i $onain more CH;C##9a < "asi$ sal= Bu..er B ha*e he smalles one& "e$ause i $onain more CH;C##H < a$i+= )H *alue o. "u..er C is a he mi++le "e$ause o. he same amoun o. CH;C##9a an+ CH;C##H in his soluion hen e a++ a$i+ HCl ino he "u..er& he )H *alue +e$rease "e$ause $on$enraion o. H/ in$reases #n he oher han+& e a++ "ase 9a#H& )H in$reases "e$ause $on$enraion o. H/ +e$reases
I@. CONC=USION
As e non he )H o. a soluion is he measure o. he $on$enraion o. $harge+ H!+rogen ions in ha gi*en soluion A soluion ih a )H loer han se*en is $onsi+ere+ o "e a$i+i$ A soluion ih a higher )H is a "ase Bu..ers ha*e he )ro)er! o mainain he )H *alue "! resising he large $hange on )H hen a++ing H/ or #H- ih ' su"-e()erimen a"o*e e $an no he meho+ o measure+ he )H& )re+i$ he )H o. he soluion an+ also he a! o $onrol his *alue .or e,uili"rium he s!sem
