titrasi asam basa -13
DESCRIPTION
Kimia AnalisisTRANSCRIPT
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Nia Kristiningrum
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Acid-Base Titration
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Titrasi asam basa adalah reaksi penetralan
Jika larutan bakunya asam disebut asidimetri
jika larutan bakunya basa disebut alkalimetri.
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Asam donor proton (ion H+)Basa penerima proton (ion H+)Penentunya adalah proton H+
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- Asam Monoprotik melepas 1 (satu) H+
- Contoh : HCl, HNO3
Asam Diprotik melepas 2 (dua) H +
Contoh : H2SO
4
Asam Poliprotik melepas > 2 H +
Contoh : H3PO
4
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Indikator
• adalah asam lemah atau basa lemah (senyawa organik) yang dalam larutannya warna molekul-molekulnya berbeda dengan warna ion-ionnya
• Indikator asam-basa terletak pada titik ekivalen dan ukuran dari pH
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www.themegallery.com Company Logo
Perubahan warna indikator
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Range of acid-base Indicators
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Contoh : kisaran pH dan perubahan warna indikator pp
asam 8,3 campuran 10 basa
tak berwarna rosa merah
Pemilihan indikator
Dipilih indikator yg mempuyai perubahan warna pada pH paling dekat dengan pH TE senyawa garam yang terbentuk
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Acid Base Titration
a solution containing a known concentration of base (or acid) is added slowly from a buret to a second solution containing an unknown concentration of acid (or base)
The progress of the titration is monitored, either by using a pH meter or by observing the color of a suitable acid–base indicator
By finding the volume of the standard solution that reacts with the measured volume of the first solution, the concentration of the first solution can be calculated
→ neutralization reaction......
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Dasar Perhitungan Volumetri
mmolek lart. standar = mmolek larutan sampel .. ( 1 )
Vst x Nst = Vx x Nx . . . . . . . . …….. ( 2 ) Dengan : Vst : volume larutan standar (terbaca dari buret ) Nst : normalitas larutan standar ( dibuat; diketahui) Vx : volume larutan sample (diambil sejumlah tertentu dengan pipet volume Nx : normalitas larutan sample
Dan : Vml x N = mmolek
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Molaritas
Normalitas
% (b/v)
volumeBM
massaM
volumeBE
massaN e
BMBE
%100)(
)(%
mLvolume
grammassakadar
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Bilangan ekivalensi dalam titrasi asam basa ditentukan oleh banyaknya H+ yang dilepaskan atau diterima
Contoh
HCl e = 1
H2SO
4 e = 2
H3PO
4 e = 3
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Untuk Titrasi Asam-Basa
VA x NA = VB x NB ….................…. (3)
atau : mmolek asam = mmolek basa
Dengan : A = asam dan B = basa
Dasar Reaksi Titrasi Asam – Basa : NETRALISASI
Reaksi : Asam + Basa Garam + Air
Contoh : (1) HCL + NaOH NaCl + H2O
(2) H2SO4 + 2 KOH K2SO4 + 2 H2O
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Titik Ekivalen (TE) dan TITIK AKHIR TITRASI (TAT)
TE : - saat reaksi antara asam dengan basa tepat
ekivalen secara stoikiometri;
- yaitu : mmolek asam = mmolek basa .
- Pada saat ini seharusnya titrasi dihentikan (secara teoritis)
TAT - Saat titrasi dihentikan
- saat terjadinya perubahan warna indikator
TAT dapat terjadi setelah atau sebelum TE, tergantung pH perubahan warna indikator dan pH larutan akhir
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Contoh .
Dititrasi 10 ml larutan as asetat 0,10 N dengan 0,10 N NaOH.
Secara teori (rumus 2) diperlukan NaOH sebanyak 10 ml ;
maka vol total = 20 ml. Dalam campuran terjadi reaksi sbb:
CH3COOH + NaOH CH3COONa + H2O
Pada TE: - NaOH dan CH3COOH habis bereaksi
- terbentuk CH3COONa = 10 ml x 0,1 N = 1 mmolek /20 ml
= 1 mmol /20 ml = 5 x 10 –2 M
pH garam = ½ (PKw + pKa + log [garam] ) ( Ka = 1 x 10 -5
= ½ (14 + 5 + log 5 x 10-2 )
= ½ ( 14 + 5 - 2 + 0,7 ) = 8,85
Sehingga indikator yang paling tepat digunakan adalah pp atau timol biru.
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Kurva Titrasi Asam-Basa
• Rex asam basa kurva titrasi tdd suatu plot pH / pOH vs (mL) titran
• Perlu dipelajari karena….1. The shape of a pH titration curve makes it
possible to identify the equivalence point in a titration, the point at which stoichiometrically equivalent quantities of acid and base have been mixed together
2. useful in selecting a suitable indicator to signal the equivalence point.
3. titration curves have certain characteristic shapes
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Kurva Titrasi Asam BasaKurva Titrasi Asam Basa
Adding NaOH from the buret to benzoic acid in the flask, a Adding NaOH from the buret to benzoic acid in the flask, a weak acid. In the beginning the pH increases very weak acid. In the beginning the pH increases very slowly.slowly.
Basa
asam
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Additional NaOH is added. pH rises as equivalence Additional NaOH is added. pH rises as equivalence point is approached.point is approached.
Basa
asam
Kurva Titrasi Asam BasaKurva Titrasi Asam Basa
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Additional NaOH is added. pH increases and then Additional NaOH is added. pH increases and then levels off as NaOH is added beyond the equivalence levels off as NaOH is added beyond the equivalence point.point.
Basa
asam
Kurva Titrasi Asam BasaKurva Titrasi Asam Basa
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Titrasi Asam kuat dengan basa kuat
Titrasi asam lemah dengan basa kuat
Titrasi basa lemah dan asam kuat
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Asam kuat senyawa yang sangat mudah melepas H+
Basa kuat senyawa yang sangat mudah melepas OH-
Asam dan basa kuat terurai sempurna dalam larutan berair
Contoh titrasi HCl dengan NaOH
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pH pada saat end point 7 (pH netral)
Indikator yang bisa digunakan
PP (phenolftalin) pH 9
BB (Bromtimol Blue) pH 7
MR (methyl Red) pH 5
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Example…
• A 43.0 mL of sodium hydroxide was titrated against 32.0 mL of 0.100 M hydrochloric acid. What is the molarity of sodium hydroxide solution?
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Answer…
• Step 1: Find the moles of hydrochloric acid:
– Mol = M x L
– Mol = 0.100 mol x .032 LL
HCl = .0032 mol
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Answer…
• Step 2: Write a balanced equation, and find the molar ratio between the acid and the base.
• HCl + NaOH NaCl + H2O
– Ratio:- HCl : NaOH1 mol : 1mol
» NaoH = 0.0032 Mol
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Answer ….
• Step 3: Find the concentration of sodium hydroxide.
– M (NaOH) = mol/ L
– M = 0.0032 mol
.043 L• NaOH = 0.0744 M
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Titrasi Asam Lemah dan Basa Kuat- ex : titration of acetic acid with NaOH
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Titrasi Basa Lemah dan Asam Kuat• - ex : titration of NH3 with HCl
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Contoh soal
Pada suatu titrasi, 50,0 mL HCl 0,100 M yang dititrasi dengan NaOH 0,100 M !
Hitunglah pH larutan pada :
a. Sebelum titrasi
b. penambahan titran 10,0 mL, 20,0 mL, 40 mL
c. Saat Titik ekivalen (penambahan 50,0 mL)
d. Penambahan 60 mL titran
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Latihan Soal…….
Pada suatu titrasi asam basa, Titran yang
dipakai adalah 0.05 M H2SO4. Yang dititrasi
adalah 10,0 ml NaOH. Volume yang
dibutuhkan untuk titrasi adalah 38,0 ml.
Berapa konsentrasi NaOH?
H2SO4 + 2NaOH Na2SO4 + 2H2O
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Ditimbang 800 mg sampel NaOH dimasukkan labu ukur 100,0 ml kemudian ditambah air sampai tanda batas, kemudian diambil 10,0 ml dg pipet volume dimasukkan erlenmeyer. Dititrasi dengan 0.05 M HCl . Volume yang dibutuhkan untuk titrasi adalah 15,0 ml. Berapa kadar (%w/w) NaOH?
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11,96 mL larutan NaOH 0,102 M digunakan untuk mentitrasi 0,0927 g suatu asam sampai titik akhir titrasi menggunakan indikator asam basa bernama fenolftalein (pp). Berapakah massa molekul asam jika asam tersebut adalah monoprotik? Jika diprotik?
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Ex. Acid-Base TitrationsEx. Acid-Base Titrations
QUESTION:QUESTION: Dipipet 10,0 ml sampel cuka dalam labu Erlenmeyer, lalu ditambahkan air sampai volume 25 ml. Dititrasi dengan NaOH 0.1 N yang sudah dibakukan. Diperoleh volume end point 7,45 ml. Berapa kadar asam cuka dalam %b/v ?
QUESTION:QUESTION: Dipipet 10,0 ml sampel cuka dalam labu Erlenmeyer, lalu ditambahkan air sampai volume 25 ml. Dititrasi dengan NaOH 0.1 N yang sudah dibakukan. Diperoleh volume end point 7,45 ml. Berapa kadar asam cuka dalam %b/v ?
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RUMUS-RUMUS pH untuk larutan asam, basa dan garam
1. Asam Kuat Valensi satu pH = - log C
2. Basa Kuat Valensi satu pOH = - log C
3. Asam Kuat Valensi banyak pH = pC – log valensi
4. Basa Kuat valensi banyak pOH = pC – log valensi
5. Asam lemah valensi satu pH = ½ pKa – ½ log C
6. Basa lemah valensi satu pOH = ½ pKb – ½ log C
7. Asam lemah valensi banyak pH = ½ pKa1 – ½ log C
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8. Campuran 2 asam lemah pH = - log {C1 + C2}
9. Campuran 2 basa lemah pOH = - log {C1 + C2}
10. Asam kuat + Basa kuat pH = 7
11. Asam lemah + Basa kuat pH = 7,0 + ½ pKa + ½ log G
12. Basa lemah + Asam kuat pH = 7,0 – ½ pKb – ½ log G
13. Asam lemah + Basa lemah pH = 7,0 + ½ pKa – ½ pKb
14. Asam lemah berlebih + Basa Kuat
pH = pKa + log [Garam] [sisa asam]
15. Basa lemah berlebih + Asam Kuat
pOH = pKa + log [Garam] [sisa basa]
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TUGAS
• Titrasi Asam kuat dg basa kuat
• Titrasi asam lemah dg basa kuat
• Titrasi basa lemah dg asam kuat
• Titrasi asam poliprotik dg basa
sertakan soal hitungan kadar beserta jawaban (3)
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