Page 73 - Statistics presented by Dr. Sara Ismail Aborass

9/8/2023

Colloidal ppts tend to peptize if washed
with pure water because water will
dilute and remove electrolytes.

Peptization is the reverse of
coagulation

Electrolyte

Colloidal solution Coagulated ppt

Peptization

To prevent peptization, add electrolyte to the
washing liquid (eg: volatile HNO3 or NH4OH)

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5) Drying and ignition

• Drying: heating the ppt at temperature
<250°C not accompanied with change
in chemical structure of ppt
Ex: AgCl

• Ignition: heating the ppt at temperature
> 250°C usually accompanied with
change in chemical structure of ppt
Ex: CaC2O4.H2O

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