What is the Difference Between Precipitation and Coprecipitation

Precipitation and coprecipitation are related processes used to separate and concentrate substances from a solution. Both occur within a solution where solutes are dissolved in a solvent. Moreover, both processes result in the creation of a solid phase from a liquid phase.

What is the difference between precipitation and coprecipitation? Precipitation is the process where a solid substance (precipitate) is formed from a solution, whereas coprecipitation is the process where impurities or secondary components are incorporated into a precipitate along with the desired primary component.

Key Areas Covered

1. What is Precipitation 
      – Definition, Features 
2. What is Coprecipitation
      – Definition, Features 
3. Similarities Between Precipitation and Coprecipitation
      – Outline of Common Features
4. Difference Between Precipitation and Coprecipitation
      – Comparison of Key Differences
5. FAQ: Precipitation and Coprecipitation
      – Answers to Frequently Asked Questions

Key Terms

Precipitation, Coprecipitation

What is Precipitation

Precipitation is a chemical process where a solid substance, known as a precipitate, forms from a solution. When the concentration of one or more substances in the solution exceeds its solubility limit, precipitation is said to occur.  The solid thus formed is called the precipitate. This process is the reverse of dissolution. In dissolution, a solid dissolves in a solvent to form a solution. There are several factors affecting precipitation. Among them are concentration, temperature, pH, and common ion effects. A higher concentration means a higher chance of precipitation. Decreases in temperature contribute to the increased precipitation. Adding a salt containing a common ion to a solution can reduce the solubility of a sparingly soluble salt.

There are many applications of precipitation across various fields. In qualitative analysis, precipitation reactions help to identify the presence of certain specific ions in the solution. For example, silver nitrate, when added to a solution containing chloride ions, will produce a white precipitate of silver chloride.

Precipitation can be used to determine the amount of a substance in a solution through gravimetric analysis. Precipitation is also useful in removing impurities from water. Apart from these uses, precipitation is also useful in the production of dyes, pharmaceuticals and pigments.

What is Coprecipitation

Coprecipitation is a process in chemistry where a substance that is normally soluble under specific conditions is carried down by a precipitate. There are two types of coprecipitation. They are surface adsorption and occlusion. In surface adsorption, ions are adsorbed onto the surface of the precipitate. These adsorbed ions may get incorporated into the crystal lattice, causing contamination. In occlusion, the impurities get trapped inside when the crystal grows rapidly.

There are several factors affecting coprecipitation such as nature of the precipitate, concentration of impurities, conditions of precipitation and washing.

Coprecipitation can interfere with the results of the analytical tests, giving inaccurate results. Coprecipitation also help to remove contaminants from water or soil. It is a method for preparing nanocomposites and certain materials with controlled properties.

Similarities Between Precipitation and Coprecipitation

1. Both processes result in the creation of a solid phase from a liquid phase.
2. Both occur within a solution where solutes are dissolved in a solvent.
3. Factors like temperature, concentration, and pH can affect both processes.

Difference Between Precipitation and Coprecipitation

Definition 

• Precipitation involves the formation of a single solid substance from a solution while coprecipitation involves the formation of a primary solid substance along with the incorporation of other substances (impurities) into the precipitate.

Result

• Precipitation aims to produce a pure precipitate of the desired compound. Coprecipitation, on the other hand, results in a contaminated precipitate with impurities trapped within the crystal lattice or adsorbed on the surface.

Mechanism

• In precipitation, there is no intentional incorporation of impurities. However, coprecipitation involves mechanisms like surface adsorption, occlusion, and inclusion of impurities into the precipitate.

Use

• Precipitation can be used for quantitative analysis, whereas coprecipitation can interfere with analytical results.

Conclusion

Precipitation is the general term where a solid substance is formed from a solution, while coprecipitation is a specific instance where unwanted substances join the main solid formed. This is the basic difference between precipitation and coprecipitation.

FAQ: Precipitation and Coprecipitation

1. What is an example of a coprecipitation?

Coprecipitation occurs when a precipitate carries down a normally soluble substance. For example, trace amounts of calcium ions can be removed from the solution by coprecipitation with magnesium oxalate.

2. What are the 4 types of coprecipitation?

There are four types of coprecipitation: surface adsorption, mixed-crystal formation, occlusion, and mechanical entrapment. These processes occur when soluble impurities become trapped within a precipitate, affecting its purity.

3. What causes Co-precipitation?

Co-precipitation occurs when a precipitate carries down a normally soluble substance. This happens due to adsorption onto the precipitate surface, incorporation into the crystal lattice, or physical trapping within the crystal structure.

4. What are the factors responsible for coprecipitation?

Coprecipitation occurs when impurities incorporate into a growing crystal lattice. Key factors include similar ion size and charge of impurity and host ion, high supersaturation of solution, rapid precipitation rate, and low temperature.

Reference:

1. “Coprecipitation – An Overview.” Science Direct.
2. “Chemical Precipitation.” Encyclopedia Britannica. 

Image Courtesy:

1. “Chemical precipitation diagram multilang” By ZabMilenko: orginalZooFari: vectorMrmw: optimized, multilang – Own work based on: Chemical precipitation diagram.svg (CC0) via Commons Wikimedia
2. “Co-precipitation” By Guruleninn – Own work (CC BY-SA 3.0) via Commons Wikimedia