1. Physical Pharmacy ADSORPTIONBy
Abdul-Wahhab Khedr
Demonstrator of Pharmaceutics & Industrial Pharmacy

2. Definition:
Adsorption is a surface process characterized by adhesion of molecules (Adsorbate) onto the surface of a solid material (Adsorbent).
Types of Adsorption:
1. Physical adsorption: in which the adsorbate is bound to the surface through the weak van der Waals forces.
2. Chemical adsorption or Chemisorption: which involves the stronger valence forces.

3. Adsorption of Oxalic acid from aqueous solutions by Talc powder
Procedure:
In a glass bottle, add 0.5 gm talc powder & 25 ml Oxalic acid solution (0.1 N or 0.3 N or 0.5 N).
Shake the bottle frequently (2 min every 10 min) in the course of 0.5 hr.
Filter the contents of the bottle, reject the first portion of the filterate, take 10 ml of the filterate and titrate with 0.5 N NaOH using Ph.Ph. as indicator (3-5 dps).
The End Point is determined by the appearance of the first permanent faint pink colour.
Calculate the amount of oxalic acid adsorbed by talc .

4. Procedure E.P = Volume of titrant used 0.5 N NaOH Filter
25 ml Oxalic acid soln
10 ml of filterate
3 dps Ph.Ph
Set aside for 8 min
0.5 gm Talc powder
Shake for 2 min

5. Calculation of Oxalic Acid adsorbed by Talc
Factor (F): is the amount of oxalic acid (in grams) neutralized by 1 ml of titrant (0.5 N NaOH).
Calculation of Factor (F): Na
+ 2 NaOH
+ 2 H2O
1 mole oxalic acid ≡ 2 moles NaOH
90 gm ≡ 1000 ml 2 M NaOH
90 gm ≡ 1000 ml 2 N NaOH
90 /4 gm ≡ 1000 ml 0.5 N NaOH
F ≡ 1 ml 0.5 N NaOH

6. Calculation of Oxalic Acid adsorbed by Talc
Total Oxalic Acid concn = Normality × Equivalent wt
= Normality × M.wt / No. of counter ions
= Normality × 90/2
= Normality × (g/l)
Adsorbed Oxalic acid = Total concn – Free concn (g)