Page 63 - Statistics presented by Dr. Sara Ismail Aborass

1- True precipitation: 9/8/2023
The impurity is precipitated togther 62
with the analyte
A) Simultaneous pption
The impurity and the analyte
deposit at the same time
Ex: AgCl (analyte) / AgBr (impurity)

(very similar Ksp so ppted at same time)
Elimination: separation or complexation

before pption

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B) Post precipitation
• Pption of impurity occur after

analyte ppt has formed
• It is due to a difference in rate of

crystallisation
• It is increased by digestion
• Ex: Impurity of Mg2+ in

determination of Ca2+ as oxalate
• So it is necessary to filter the

analyte ppt as soon as its pption is
complete
• Elimination: separation or
complexation before pption

124