The graph of log(x/m) v/s Log C is a straight line, where log k is intercept and 1/n is the slope. The graph of adsorption at constant temperature is known as Freundlich adsorption isotherm.

1. SHREE MALLIKARJUN COLLEGE CLASS:SYBSC
SAFETY: Refer to MSDS of oxalic acid, potassiumpermanganate, sodium hydroxide, phenolphthalein
-Dr. Mithil S. FalDesai
Aim: Verification of Freundlich adsorption isothermof Coconut shell Carbon.
Chemicals: Oxalic acid, potassiumpermanganate, sodium hydroxide, phenolphthalein
Apparatus: Standard volumetric flask, burette, pipette, beakers, funnel, measuring cylinder, dropper, reagent bottle
Theory: Adsorption depends on temperature, chemical nature, surface area and concentration of adsorbate. At a
constant temperature variation in adsorption is given by following empirical relation
𝑥
𝑚
= 𝑘𝐶1/𝑛
----- eq 1
Where x, m and C are the amount of adsorbate, the mass of adsorbent and equilibrium concentration of adsorbate,
respectively. The n and k are constant. The eq 1 can be written as
log(x/m)= log k + 1/n log C ----- eq 2
Thus the graph of log(x/m) v/s Log C is a straight line, where log k is intercept and 1/n is the slope. The graph of
adsorption at constant temperature is known as Freundlich adsorption isotherm.
Procedure:
1) Take seven clean 250 ml glass stoppered bottles and label themA to G.
2) Transfer 0.1 N oxalic acid solution and distilled in these bottles as given in Table 1.
3) Place the bottle in a water bath to attain roomtemperature.
4) Add 1 g charcoal in each bottle and shake.
5) Keep the bottles in a water bath for 30 min.
6) Filter the content.
7) Titrate the 10 mL of filtrate against standardized KMnO4 or NaOH.
Observation:
Table 1.
B.
No.
m=
Amount
of
charcoal
(g)
Volume
of
Oxalic
acid
(mL)
Volume
of
Water
(mL)
Burette
reading
for
KMnO4
(mL)
A = Amount
of oxalic
acid in 100
mL before
adsorption
(g)
C= Amount
of oxalic
acid in 100
mL filtrate
after
adsorption
(g)
x=
Amount
of oxalic
acid
adsorbed
A - B (g)
Log
C
x/m Log
(x/m)
A 50 50
B 40 60
C 30 70
D 25 75
E 20 80
F 10 90
Results: If the graph of log(x/m) as ordinate and log C as abscissa is a straight line proves the Freundlich adsorption
isotherm for adsorption of oxalic acid on charcoal.
Further reading
1) Experiments in Applied Chemistry, S. Rattan, S. K Kataria, and Sons.