Rangkuman materi Larutan Penyangga (Buffer)

1. MEMBUAT LARUTAN PENYANGGA
1. Larutan Penyangga HA/Aa. Asam Lemah dan Garamnya
CH3COOH
asam lemah
CH3COONa
garam asam lemah
H+ +
CH3COO-
Na+ +
CH3COObasa konjugasi
Larutan Penyangga
CH3COOH/CH3COO- Komponen asam CH3COOH dalam larutan penyangga berasal dari asam lemah
CH3COOH yang terurai sedikit sekali.
- Komponen basa CH3COO- dalam larutan penyangga dianggap hanya berasal dari
garam asam lemah, CH3COONa yang terurai sempurna.
b. Asam Lemah Berlebih + Basa Kuat
CH3COOH
+ NaOH
asam lemah berlebih
basa kuat
CH3COOH
asam lemah sisa
CH3COONa
garam asam lemah
CH3COONa
+
garam asam lemah
H+ +
Na+ +
H2O
CH3COOCH3COObasa konjugasi
Larutan Penyangga
CH3COOH/CH3COOAsam lemah CH3COOH berlebih akan bereaksi dengan basa kuat NaOH membentuk
garam CH3COONa.
- Komponen asam CH3COOH dalam larutan penyangga berasal dari sisa asam lemah
CH3COOH yang hanya terurai sedikit sekali.
- Komponen basa CH3COO- dalam larutan penyangga dianggap hanya berasal dari
garam asam lemah, CH3COONa yang terurai sempurna.

2. c. Garam Asam Lemah Berlebih + Asam Kuat
CH3COONa + HCl
Garam asam
Asam
lemah berlebih kuat
CH3COOH
asam lemah
CH3COONa
garam asam lemah
CH3COOH + NaCl
Asam lemah
H+ +
Na+ +
CH3COOCH3COObasa konjugasi
Larutan Penyangga
CH3COOH/CH3COOGaram asam lemah CH3COONa berlebih akan bereaksi dengan asam kuat HCl
membentuk asam lemah CH3COOH.
- Komponen asam, CH3COOH dalam larutan penyangga berasal dari asam lemah
CH3COOH yang terurai sedikit sekali.
- Komponen basa CH3COO- dalam larutan penyangga dianggap hanya berasal dari
sisa garam asam lemah, CH3COONa yang terurai sempurna.
2. Larutan Penyangga B/BH+
a. Basa Lemah dan Garamnya
NH3
+ H2O
basa lemah
NH4Cl
garam basa lemah
NH4+ +
OH-
NH4+
asam konjugasi
+ Cl-
Larutan Penyangga
NH3/ NH4+
- Komponen basa NH3 dalam larutan penyangga berasal dari sisa basa lemah NH3
yang terurai sedikit sekali.
- Komponen asam NH4+ dalam larutan penyangga dianggap hanya berasal dari garam
basa lemah, NH4Cl yang terurai sempurna.

3. b. Basa Lemah Berlebih + Asam Kuat
NH3
+ HCl
NH4Cl
basa lemah asam garam basa lemah
berlebih
kuat
NH3
+ H2O
basa lemah
sisa
NH4Cl
garam basa lemah
NH4+ + OH-
NH4+
asam konjugasi
+ Cl-
Larutan Penyangga
NH3/ NH4+
Basa lemah NH3 berlebih akan bereaksi dengan asam kuat HCl membentuk garam
NH4Cl.
- Komponen basa NH3 dalam larutan penyangga berasal dari sisa basa lemah NH3
yang terurai sedikit sekali.
- Komponen asam NH4+ dalam larutan penyangga dianggap hanya berasal dari garam
basa lemah, NH4Cl yang terurai sempurna.
c. Garam Basa Berlebih + Basa Kuat
NH4Cl
+ NaOH
garam basa lemah
basa
berlebih
kuat
NH3
+ H2O
basa lemah
NH4Cl
garam basa lemah
NH4OH
+ NaCl
basa lemah
NH4+ + OHNH4+
asam konjugasi
+ Cl-
Larutan Penyangga
NH3/ NH4+
Garam basa lemah NH4Cl berlebih akan bereaksi dengan basa kuat NaOH
membentuk basa lemah NH4OH.
- Komponen basa NH3 dalam larutan penyangga berasal dari basa lemah NH3 yang
terurai sedikit sekali.
- Komponen asam NH4+ dalam larutan penyangga dianggap hanya berasal dari garam
basa lemah, NH4Cl yang terurai sempurna.

4. SUMMARY OF BUFFER SOLUTION
1. A buffer solution is an aqueous solution that can maintain the pH of a system within a
specified range when a small amount of acid or base is added, or when the system is
diluted.
2. A buffer solution has acid and base components that generally take the form of conjugate
acid-base pairs: weak acid and its conjugate base (HA/A-) or weak base and its
conjugate acid (B/BH+).
3. The equilibrium of acid and base components in buffer solutions.
Buffer solution HA/A+ is composed of weak acid (HA) and its salt (MA)
HA(aq)
H+(aq) +
AAcid component
Base component
from weak acid
from salt MA
Buffer solution B/BH+ is composed of weak base (B) and its salt (BHA)
B(aq)
+
H2 O
BH+(aq)
+
OHBase component
Acid component
from weak base
from salt MA
4. The way buffer solutions work upon the addition of a small amount of acid or base or
when dilution takes place.
Buffer Solution HA/ABuffer Solution B/BH+
The acid H+ added will be
Adding small The acid H+ added will be
neutralized by the base component, neutralized by the base component,
amount of
A-.
B.
acid (H+)
H+
Acid
being added
Adding small
amount of
base (OH-)
HA
Base component
of buffer solution
-
Base
being added
+
HA
Acid component
of buffer solution
H+
Acid
being added
The base OH added will be
neutralized by the acid component,
HA.
OH-
Dilution
(adding H2O)
A-
+
A- + H2O
Dilution will affect the moles of H+
(H3O+) and OH- in the system,
which will cause a shift in the
buffer solution equilibrium. The
effects of dilution can be observed
only if the value of Ka is relatively
large and the concentrations of the
components are very small.
+
B
BH+
Base component
of buffer solution
-
The base OH added will be
neutralized by the acid component,
HA.
OHBase
being added
+
HA
Acid component
of buffer solution
A- + H2O
Dilution will affect the moles of H+
(H3O+) and OH- in the system,
which will cause a shift in the
buffer solution equilibrium. The
effects of dilution can be observed
only if the value of Kb is relatively
large and the concentrations of the
components are very small.

5. 5. The buffer capacity of a solution refers to its ability to resist changes in pH upon the
addition of acid/base or dilution. The capacity of a buffer solution is determined by the
concentrations of the acid and base components and their concentration ratio. The
optimum capacity is obtained when the concentrations of the acid and base components
are the same or equimolar.
6. Preparing buffer solutions HA/A- and B/BH+
Buffer Solution HA/ABuffer Solution B/BH+
Weak acid + its salt
Weak base + its salt
Excess weak acid + strong base
Excess weak base + strong acid
Excess salt of weak acid + strong acid
Excess salt of weak base + strong base
7. Important buffer systems in human bodies: haemogobin, phosphate H2PO4-/HPO42-, and
carbonate H2CO3/HCO3-.
SUMMARY OF FORMULA
The Henderson-Hasselbach Equation
Buffer Solution HA/A-
Buffer Solution B/BH+
Sumber:
Johari, J.M.C. dan M. Rachmawati. (2010). Chemistry 2B for Senior High School Grade XI
Semester 2. Jakarta : Esis – PT. Penerbit Erlangga.