Adsorption Isotherm Calculation

Preparation of 0.2 N Oxalic Acid stock solution (250 mL SMF):

Equivalent weight of Oxalic Acid = 63 g/eq

Amt. taken                  = _________ g

Strength of oxalic acid = (Amount taken x 1000 mL) / (63 g/eq x 1 L x 250 mL)

Strength of oxalic acid = ________________ N

Table I Distribution of stock solution

Bottle Number	Volume of acid (mL)	Volume of Water (mL)	Concentration of acid (N2)
1	10	40
2	20	30
3	30	20
4	40	10

Calculation:

Volume of acid (V1) x Concentration of acid (N1) = Total volume of solution (V2) x New strength of Acid (N2)

     For example, Bottle number 1

     10 mL x 0.2 N = 50 mL x N2

     N₂ = 0.04 N

Table II Determination of equilibrium concentration

Bottle Number	Volume of Acid (mL)	Burette reading (mL)		Volume of NaOH (mL)	Ceq
		Initial (mL)	Final (mL)
1	10 mL	0	4.8	4.8
		0	4.8
		0	-----
2	10
3	10
4	10
5	10
6	10

 

Standardisation of NaOH solution:

Volume of NaOH x Strength of NaOH (N2) = Volume of Acid x Strength of Acid

Calculation of Ceq

Bottle I to VI

Volume of NaOH x Strength of NaOH = Volume of Acid x C_eq

Table III Determination of unknown concentration

Bottle No.	Ini. Conc. (Ci)	Eq. Conc. (Ceq)	Ad. Conc. (Cad)	x	m	x/m	-log (x/m)	-log Ceq
1
2
3
4
5	Unknown
6	Unknown

 

Calculation:
Conc. (C_ad) = Ini. Conc. (C_i) - Eq. Conc. (C_eq)
x (Amount of mass adsorbed) = (Ad. Conc. (C_ad) N * 63 g/eq ) / 20
m = Mass of Activated charcoal

Freundlich’s equation:

x / m

= kC^1/n

Where,
                x = Mass adsorbed
                m = Mass of activated charcoal
                k = Adsorption coefficient
                n = constant
On taking logarithm
log x/m = log k + 1/n log C

Bottle No. V

From graph

-log x/m   = _____
x               = _____ g
C_ad               = _____ N                    C_ad= x . 20 / 63  
C_i                  = _____ N   

Bottle No. VI

From graph
-log x/m      = _____
x                = _____ g
C_ad               = _____ N   
C_i                   = _____ N   

Result

The unknown concentration of oxalic acid
                                                I              =______ N
                                                II             =______ N
Adsorption coefficient (k)          =
Order of adsorption (n)               =