ARGENTOMETRI 2014

8/16/2019 ARGENTOMETRI 2014

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ARGENTOMETRI


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ARGENTOMETRI

• Definisi :Analisis titrimetri dengan

baku AgNO3

• Dasar Reaksi :Reaksi Pengendapandengan ion Ag+ Reaksipresipitasi

• Perlu pemahaman hasil kali kelarutan


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Precipitation Reactions

Precipitation is the formation of a solid ina solution

solid formed is called the precipitate

A precipitation reaction occurs whenwater solutions of two dierent ioniccompounds are mied and an insolu!lesolid separates out of solution"

E# $%l & A#NO' A#%l &$NO'

%l) solution Precipitatin# a#ent precipitate

http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solid


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*olu!ilit+ of precipitate

• *olu!ilit+ of a compound , concentrationsof a solu!le species at e-uili!rium with itsinsolu!le form"

• If the compound is sparin#l+ solu!le. it willproduce cation / anion"

• E# A#%l sli#htl+ dissol0ed in water" *o A#%l

has a specic solu!ilit+. s , solid phase a-, a-ueous phase

A#%l s3 A#& a-3& %l) a-3


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• The e-uili!rium constant for the reaction is4nown as solu!ilit+ product constant"

$ sp A#%l3 , 5A#&65%l)6

• %oncentration of an+ solid A#%l3 is

constant and is com!ined in thee-uili!rium constant to #i0e $ sp

• *olu!ilit+ product constants are used todescri!e saturated solutions of ionic

compounds of relati0el+ low solu!ilit+"• A saturated solution is in a state of

d+namic e-uili!rium !etween thedissol0ed. dissociated. ionic compound

and the undissol0ed solid"


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Precipitation titration

• Precipitation titration is a titration method!ased on the formation of precipitate.which is sli#htl+ solu!le

• Titration with precipitatin# a#ents is usefulfor determinin# certain anal+tes. pro0idedthe e-uili!rium will ta4e place rapidl+ andsuita!le means of detectin# e-ui0alentpoints is a0aila!le

• Titration cur0e 8 plot of the chan#es inanal+te concentration a#aints titrant

0olumes"


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• %onsider titration of %l) with a standardsolution of A#NO'"

• Titration cur0e prepared !+ plottin# p%l)lo#5%l)63 a#aints the 0olume of A#NO' in a manner similar to acid!ase

titration"• 9efore titration started 8 onl+ ha0e %l)"

p%l , ) lo#5%l)6

• Titration proceed 8 part of %l) is remo0edfrom solution !+ precipitation as A#%l"

p%l , )lo# 5remainin# %l)6


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• At e-ui0alence point ) we ha0esolution a saturated solution of A#%l"

5%l)6, :$ sp

• Ecess A#NO'

added 8 ecess A#&"

5%l)6 is determine from theconcentration of A#& and $ sp"

5%l)

6 , $ sp;5A#&

6


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Example 1

%alculate p%l for the titration of1


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solution

a3 Addition of


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!3 Addition of 2


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c3 Addition of =="< ml A#

Initial mmol %l) , 1"


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d3 Addition of 1


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Addition of 1


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Titration cur0e for the titration of 1


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Titration Curves or Argentometric !et"ods

Plots o titration curves are normall$ sigmoidal curvesconsisting o pAg %or pAnal$te& versus volume o AgNO

3 solution

added'

Example( Titration o c"loride )it" silver'

T"e points on t"e curve can be calculated* given t"e anal$teconcentration* AgNO

3 concentration and t"e appropriate

sp'


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soal

• %alculate the titration cur0e for thetitration of >


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$IMIA ANACI*I* !+ Dah+u 1?

HUBUNGAN MOL VS GRAEK

1 ,raek - 1 mol ion Ag+

Cl. + Ag+ AgCl 1 mol "alida - 1 ,raek

CN. + Ag+ AgCN

CN.+ AgCN Ag%CN&/.

/CN.+ Ag+ Ag%CN&/

. 1 mol CN. - 0 ,raek


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$IMIA ANACI*I* !+ Dah+u 1=

Indikator :on $ang dapat

mengendap dengan ion larutanbaku* memberikan )arna $angmuda" larut dibanding ion $ang

dianalisis'

Contoh : ~CrO2/ pada titrasi "alida.

dg Ag+

- 4e3+ pada titrasi Ag+ dg CN5.


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$IMIA ANACI*I* !+ Dah+u 21

BEBERAPA METODAARGENTOMETRI

A. Metode Mohr• !etode titrasi langsung

• 5uasana larutan netral atau agak

alkalis• Cocok untuk penetapan Cl.

• ndikator kalium kromat % /CrO2&

•

Titi4 ak"ir titrasi ( ter:adi endapanmera" Ag/CrO

2


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$IMIA ANACI*I* !+ Dah+u 22

Reaksi :

Cl. + Ag+ AgCl ↓putih sp AgCl ; 1*

1>

CrO2

/ + /Ag+ Ag/CrO

2 ↓merah

sp Ag/CrO2 ;

x 1>1/ Catatan :

d 5uasana tidak bole" asam* sebab dalamsuasana asam CrO

2/ 6CrO

2 Cr/O@

/*

akibatn$a CrO2

/ berkurang endapan

Ag/CrO

2 lambat terbentuk kesala"an

besar

d ika suasana alkalis %p6B?&* ion Ag+ akanmembentuk endapan "itam

Ag+ + O6. AgO6 % Ag/O↓ + 6/>&


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$IMIA ANACI*I* !+ Dah+u 2'

Ksp AgCl > Ag2CrO4 , tetapi kelarutan AgCl <

Ag2CrO

4 karena AgCl biner, sedangkan Ag

2CrO

4

terner

sp AgO6 ; /*= x 1>

alau pada titik ak"ir DAg+ ; /*/ x 1> :adi

DO6. B 1*/ x 1>3

adi* pO6 F /*? p6 B 11*1

:ika p6 F ?* Ag+ tidak mengendap


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$IMIA ANACI*I* !+ Dah+u 2B

B. Metoda Volhard

• !etoda titrasi tidak langsung

• 5uasana "arus asam %p6 F 3* >*1/

3+ .


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$IMIA ANACI*I* !+ Dah+u 2>

• p6 "arus renda"* krn 4e3+ dapatmengendap pada p6 B 3 4e%O6&

3'

Akibatn$a titik ak"ir sukar teramati• Pd penetapan kadar Cl.* endapan AgCl

perlu dipisa"kan sebelum kelebi"an

baku Ag+

dititrasi kembali denganN625CN* sebab kelarutan AgCl B Ag5CN

AgCl + 5CN. Ag5CN ↓ + Cl

• Pada titrasi ion 8r.* endapan Ag8rtidak perlu dipisa"kan* karenakelarutan Ag8r F Ag5CN

8r. sp Ag8r

; ; >*==


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2@

• Pada titrasi .* endapan Ag :uga tidakperlu dipisa"kan karena kelarutan Ag

FFF Ag5CNTetapi penamba"an indikator 4e3+ ditamba"kan setela" semua ion . diendapkan* agar tidak ter:adi reaksi (

/ 4e3+ + / . / 4e/+ + /

C. Metoda Fajans• !etoda ini mirip pada metoda !o"r*

tetapi indikator $ang digunakan berupaindikator adsorbsi ( eosin


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End-Point Detection

1"3 Precipitation Titration aFans titration

) ses an adsorption indicator

Precipitate surface is initiall+ne#ati0el+ char#ed due to ecess%l)

A#%l ppt"

After e-ui0alence point end point3.

ha0e ecess A#& so surface is nowpositi0el+ char#ed"

Anionic d+e is attracted to positi0e char#ed

surface" Adsorption of d+e causes colorchan e

A#%l ppt"


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End-Point Detection

1"3 Precipitation Titration aFans titration Anionic d+es

) MaimiHe surface area hi#her !indin# stron#er color chan#e) small particle siHe low concentration

) most use appropriate p to maintain ne#ati0e char#e

%han#es from #reenish +ellow to pin4*harper color transition. !inds to ti#htl+ to %l )


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2=

D. Metoda Liebig• Titrasi langsung•

Prinsip reaksi kompleks• Tanpa indikator* "arus bebas N63• Intuk penetapan kadar ion 5ianida

Komentar :• Reaksi :

Ag+ + CN. AgCN

AgCN + CN.

Ag%CN&/.

Ag%CN&

/. + Ag+ AgDAg%CN&

/ ↓5ebagai

titik ak"ir

Harus bebas NH3, sebab NH

3 membentuk

kompleks dengan Ag+ Ag(NH3)2+


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Titration %ur0e *hape


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Shape of Titration Curve1"3 E-ui0alence point is the steepest point of the cur0e"

Point of maimum slope inJection point second deri0ati0e is Hero

0 dx

y d :int poInflection

valuegreatest reachesdx

dy :slopeSteepest

2

2



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Shape of Titration Curve2"3 Aect of $ sp on Titration %ur0e"

Cowest solu!ilit+ #i0es steepest chan#e at e-ui0alence point

Ma#nitude of concentrationchan#e and ease ofidentif+in# e-ui0alencepoint increases with $ sp



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Titration of Mitures

• Endpoints are characteriHed !+inJection points where a cur0aturechan#es si#n"

• In mitures leadin# to twoprecipitates. two inJection points areo!ser0ed" – The lowest $ sp solid nishes its reaction

!+ precipitatin# rst" Thus the rstinJection point"

–

The more solu!le solid precipitates last"


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Titration of a Miture

• The less solu!le product forms rst

• If there is suKcient dierence insolu!ilit+ of products – irst precipitation is nearl+ complete

!efore the second one !e#ins• *eparation !+ precipitation

–

%oprecipitation• Alters the epected endpoints


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Titration of a MitureEample


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Titrations End-Point Detection

2"3 T+pical Applications Also indicates potential sources of interference

) other ions;anal+tes ma+ !e present in sample


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• 9erapa L 4adar 4adar Na%l dalamair laut Fi4a 2>.< ml A#NO'


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• B mC asamnitrat pe4at. dan ditam!ah4an2>.


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ARGENTOMETRI 2014

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