Titrasi Aasam Basa (1)

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Acid Base Titrations


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Titration Curve

A titration curve is a plot of pH vs. the

amount of titrant added. Typically the

titrant is a strong (completely)dissociated acid or base. Such curves

are useful for determining endpoints

and dissociation constants of ea!acids or bases.


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"eatures of the Strong Acid#Strong Base

Titration Curve

1. The pH starts out low, reflecting the high [H3O+] of the

strong acid and increases gradually as acid is neutralized

by the added base.

. !uddenly the pH rises steeply. This occurs in the

i""ediate #icinity of the e$ui#alence point. %or this type

of titration the pH is &.' at the e$ui#alence point.

3. (eyond this steep portion, the pH increases slowly as "orebase is added.


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Sample Calculation$ Strong Acid#Strong

Base Titration Curve

Problem 24-1.)onsider the titration of *'.' " of '.1''

H)l with '.1'' -aOH.

Region 1.(efore the e$ui#alence point, after adding '.' " of

'.1'' -aOH. Half way to the e$ui#alence point./0nitial "oles of H3O

+

2 oles of OH2added

baseaddedof#olu"eacidof#olu"eoriginalre"ainingOHof"ol/a"ount]O[H 33

+

=

+

+


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Base Titration Curve (Cont. %)

Region 2.t the e$ui#alence point, after adding *'.' " of '.1''

-aOH.

0nitial "oles of H3O+ '.'*'' 4 '.1'' '.''*'' H3O

+

2 oles of OH2added '.'*'' 4 '.1'' '.''*'' "ol OH2

baseaddedof#olu"eacidof#olu"eoriginal

re"ainingOHof"ol/a"ount]O[H 33

+

=

+

+


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Base Titration Curve (cont. %%)

Region 3.fter the e$ui#alence point, after adding 5'.' " of '.1'' -aOH. -ow calculate e4cess OH2/

Total "oles of OH2 '.'5'' 4 '.1'' '.''5'' "ol OH2

2oles of H3O+consu"ed '.'*'' 4 '.1'' '.''*'' "ol


re"ainingOHof."ol/a"ount][OH

+

=


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H6r 6ropionic cid


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Contoh soal $

Hitung pH pada &' &' *' *& dan +& titran pada titrasi

*& m, &'&& - asam asetat dengan &' - a/H.


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Titration of Weak Base with Strong Aci

[H+] = KaF

F=( FVi) / (Vi+Va)

[OH] = KbF = KwF /Ka

F=( FVi) / (Vi+Va)

Equivalence point

Ate! equivalence point

(Va"Ve)

pH = p#b+ lo$[%H&+]/[%H']

pH = pKa+ lo$ [A] /[HA]

eo!e te equivalencepoint (*V aV e)

[OH,] = KbF =-.&-*'[H+] = KaFnitial

+ H0O 1 H++ OH,HA + OH,1 H0O + A

,2it!ation !eaction

3ea4 a5e wit 6t!on$ a5e3ea4 Aci7 wit 6t!on$ a5e

(Vi+ Va)8

(Va Ve)9FH:l=[H

+]

(Vi+ Va)8

(Va Ve)9F%aOH=[OH

,]

!om"arison of Weak Aci# Base with Strong Base#Aci


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0agam !urva titrasi $ berdasar titi! e1uivalen

antara asam lemah dengan basa !uat

.2onsentrasi asam lemah yang dititrasi

(&'&& 3 &'&& 3 &'&& -)

. Asam dengan perbedaan nilai 2a(sema!in !ecil 2a ###4 asam sema!in lemah

ma!a a!an menyebab!an titi! e1uivalen tida!

didapat!an)


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The four -a5or 6ifferences Beteen a Strong Acid#

Strong Base Titration Curve and a 7ea! Acid#Strong


1. The initial pH is higher.

. gradually rising portion of the cur#e, called

the buffer region, appears before the steep rise

to the e$ui#alence point.

3. The pH at the e$ui#alence point is greater than

&.''.

*. The steep rise inter#al is less pronounced.


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Sample Calculation$ 7ea! Acid#Strong



H6r 7a 1.3 4 1'25/ with '.1'' -aOH.

Region 1.The solution of wea8 acid to be titrated, before any

base is added.

!olution9

ns9


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Base Titration Curve (Cont.%)


H6r 7a 1.3 4 1'25/ with '.1'' -aOH.

Region 2.fter 3'. " of base total/ has been added. This is

clearly in the buffer region of the titration cur#e.

!olution9 :efer to ecture 3.

)an use the calculator progra", ;(uf< de#eloped in lecture 3. (ut

first "ust calculate the no"inal a"ounts of acid and base for"s of

the wea8 acid created by addition of the strong base. These are9[H]'

[2]'

ns9 %ro" buffer progra"9 "$ %


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Base Titration Curve (Cont.ll)


H6r 7a 1.3 4 1'25/ with '.1'' -aOH.

Region 3.fter *'. " of base total/ has been added. This is

clearly at the e$ui#alence point of the titration cur#e.

!olution9 :efer to ecture 3.

)an use the calculator progra" de#eloped in lecture 3. (ut first

"ust calculate the no"inal a"ounts of acid and base for"s of the

wea8 acid created by addition of the strong base. These are9

[H]'

[2]'

ns9 %ro" buffer progra"9 "$ %


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Base Titration Curve (cont. %%l)

Region 4.fter the e$ui#alence point, after adding 5'.' " of '.1'' -aOH. -ow calculate e4cess OH2/

Total "oles of OH2

2oles of wea8 acid consu"ed

oles of OH2re"aining


tinneutralizaafterre"ainingOHof."ol/a"ount][OH

+

=


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The four -a5or 6ifferences Beteen a 7ea!

Acid#Strong Base Titration Curve and a 7ea!

Base#Strong Acid Titration Curve1. The initial pH is abo#e &.''.

. gradually decreasing portion of the cur#e,

called the buffer region, appears before asteep fall to the e$ui#alence point.

3. The pH at the e$ui#alence point is less than

&.''.

*. Thereafter, the pH decreases slowly as

e4cess strong acid is added.


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"eatures of the Titration of a

8olyprotic Acid ith a Strong Base

1. The loss of each "ole of H+shows up as

separate e$ui#alence point but only if the

two p7a

s are separated by "ore than 3 p7

units/.

. The pH at the "idpoint of the buffer region

is e$ual to the p7aof that acid species.

3. The sa"e #olu"e of added base is re$uired

to re"o#e each "ole of H+.


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Acid#Base %ndicators and the

-easurement of pH

= >efinition9 wea8 organic acid, H0n that has a differentcolor than its con?ugate base, 0n2, with the color change

occurring o#er a specific and relati#ely narrow pH range.

= Typically, one or both for"s are intensely colored, so only

a tiny a"ount of indicator is needed, far too little toperturb the pH of the solution.

= !ince the indicator "olecule is a wea8 acid, the ratio of the

two for"s go#erned by the [H3O+] of the test solution9

[ ][ ][ ]

[ ]

[ ]

[ ]

[ ]a

3

2

3a3

7

OH

0n

H0n9Therefore

H0n

0nOHH0nof7/.0n/.OH/O.H/H0n.

+

+

+

=

=+=+ aqaqlaq


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,et us consider 1uantitatively' the case of titrating a ea!

acid ith a strong base. %f the ea! acid has one

dissociable proton' then the overall reaction is$

HA 9 /H#: A#9 H&

7e ill assume that the strong base a/H and the ea!

acid anion aA are completely dissociated in solution.

"urthermore' e ill not neglect the contribution of the

dissociation of ater.


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/ur Titration System is ;overned by

"our


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= !uch a syste" has @ e4peri"entally "easurable#ariables9 7a, 7w, [H]'and [-aOH]'

= 0f we assu"e that the first four 7a, 7w, [H]'and

[-aOH]'/ are 8nown, then we are left with *

e$uations in * un8nowns.

= Of the * un8nowns, the only one we cancon#eniently "easure is [H+]. This suggests that

we sol#e the four e$uations for [H

+

] by successi#eeli"ination.


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The


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nswers

1. :egion 1, pH 1.*&&, :egion , pH &.''', :egion 3,pH 1.'*C

. :egion 1, pH .D5 , :egion , pH 5.3C , :egion 3,

pH @.&D , :egion * 1.'5

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