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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Sample Calculation$ Strong Acid#Strong
Base Titration Curve (Cont. %)
Region 2.t the e$ui#alence point, after adding *'.' " of '.1''
-aOH.
0nitial "oles of H3O+ '.'*'' 4 '.1'' '.''*'' H3O
+
2 oles of OH2added '.'*'' 4 '.1'' '.''*'' "ol OH2
baseaddedof#olu"eacidof#olu"eoriginal
re"ainingOHof"ol/a"ount]O[H 33
+
=
+
+
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Sample Calculation$ Strong Acid#Strong
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
baseaddedof#olu"eacidof#olu"eoriginal
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
Base Titration Curve
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
Base Titration Curve
Problem 24-2.)onsider the titration of *'.' " of '.1''
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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Sample Calculation$ 7ea! Acid#Strong
Base Titration Curve (Cont.%)
Problem 24-2.)onsider the titration of *'.' " of '.1''
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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Sample Calculation$ 7ea! Acid#Strong
Base Titration Curve (Cont.ll)
Problem 24-2.)onsider the titration of *'.' " of '.1''
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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Sample Calculation$ Strong Acid#Strong
Base Titration Curve (cont. %%l)
Region 4.fter the e$ui#alence point, after adding 5'.' " of '.1'' -aOH. -ow calculate e4cess OH2/
Total "oles of OH2
2oles of wea8 acid consu"ed
oles of OH2re"aining
baseaddedof#olu"eacidof#olu"eoriginal
tinneutralizaafterre"ainingOHof."ol/a"ount][OH
+
=
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The four -a5or 6ifferences Beteen a 7ea!
Acid#Strong Base Titration Curve and a 7ea!
Base#Strong Acid Titration Curve1. The initial pH is abo#e &.''.
. gradually decreasing portion of the cur#e,
called the buffer region, appears before asteep fall to the e$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