The key difference between coprecipitation and post precipitation is that in coprecipitation, precipitation of an undesired compound occurs along with the precipitation of the desirable compound whereas, in post precipitation, the precipitation of an undesirable compound occurs after the precipitation of the desirable compound.
The term precipitation refers to the formation of a solid mass from a solution after treating the solution with some chemicals. Coprecipitation and post precipitation are two types of precipitation process that have both advantages and disadvantages, depending on the situation and purpose of the analysis.
CONTENTS
1. Overview and Key Difference
2. What is Coprecipitation
3. What is Post Precipitation
4. Side by Side Comparison – Coprecipitation vs Post Precipitation in Tabular Form
5. Summary
What is Coprecipitation?
Coprecipitation is a type of precipitation where soluble compounds in a solution are removed during the course of precipitation. There are three major types of coprecipitation methods. These are the surface adsorption, mixed crystal formation, and mechanical entrapment.
Surface adsorption refers to the formation of the precipitate of the undesired compound on the precipitate of the desirable compound as an adsorption process. For example, the formation of coagulated colloids; in the reaction between silver nitrate and sodium chloride, the desribale product is the silver chloride precipitate. Here, silver ions form precipitates with other ions present in the solution.
Figure 01: Silver Halide Precipitation
Mixed crystal formation is another type of coprecipitation where the contaminated ion is replaced by an ion-containing crystal. For example, in the precipitation of barium sulfate from barium chloride, coprecipitation of lead sulfate also occurs if the solution contains lead ions. In mechanical entrapment method, undesirable ions get entrapped in the voids of the precipitate that is being formed.
What is Post Precipitation?
Post precipitation is a type of precipitation where the precipitation of the undesirable compound occurs after the formation of the precipitate of the desirable compound. This type of precipitation occurs on the surface of the first precipitate. For example, the formation of calcium oxalate after the precipitation of magnesium oxalate.
What is the Difference Between Coprecipitation and Post Precipitation?
Precipitation is the formation of a solid mass from a solution after treating the solution with some chemicals. Coprecipitation is a type of precipitation where soluble compounds in a solution are removed during the course of precipitation. Post precipitation is the precipitation of a second, often related, substance upon the surface of an initial precipitate. So, the key difference between coprecipitation and post precipitation is that in coprecipitation, precipitation of an undesired compound occurs along with the precipitation of the desirable compound whereas, in post precipitation, the precipitation of an undesirable compound occurs after the precipitation of the desirable compound.
Consequently, the contamination from impurities is high in coprecipitation compared to post precipitation. An example for coprecipitation is the precipitation of silver ions with other ions during the silver chloride precipitation; an example for post precipitation is the formation of calcium oxalate after the precipitation of magnesium oxalate.
Below infographic summarizes the difference between coprecipitation and post precipitation.
Summary – Coprecipitation vs Post Precipitation
Coprecipitation and post precipitation are two types of precipitation. The key difference between coprecipitation and post precipitation is that in coprecipitation, precipitation of an undesired compound occurs along with the precipitation of the desirable compound whereas, in post precipitation, the precipitation of an undesirable compound occurs after the precipitation of the desirable compound.
Reference:
1. “Gravimetry.” LinkedIn SlideShare, 7 Sept. 2014, Available here.
2. “Coprecipitation and Post Precipitation.” Prezi. com, Available here.
3. Coprecipitation.” Wikipedia, Wikimedia Foundation, 18 Dec. 2019, Available here.
Image Courtesy:
1. “Common Silver Halide Precipitates” By Cychr – I took the photograph after completing the reactions (CC BY 3.0) via Commons Wikimedia