Precipitation Reactions | Inorganic Chemistry PDF Download

Introduction

Chemical reactions involve chemical changes that result in the formation of new compounds under some specific conditions. Chemical equations can help us understand the chemical reactions between various elements or compounds. Chemical equations show the reactants and the products that are involved in these reactions. The compounds that participate in a chemical reaction are called reactants. The reactants might be in the solid, gaseous, or liquid phase.

What is Precipitation Reaction

Many chemical reactions occur in our daily lives. Common examples of such reactions are burning, corrosion, cooking of food and digestion. One important class of chemical reactions are precipitation reactions. In such reactions, two different soluble salts (which are in aqueous solutions) combine to form two products. One of these products is insoluble in the solution and is precipitated out (and is, therefore, referred to as the ‘precipitate’).

Precipitation Reaction – Definition and Meaning

The term ‘precipitation reaction’ can be defined as “ a chemical reaction occurring in an aqueous solution where two ionic bonds combine, resulting in the formation of an insoluble salt”. These insoluble salts formed in precipitation reactions are called precipitates. Precipitation reactions are usually double displacement reactions involving the production of a solid form residue called the precipitate. These reactions also occur when two or more solutions with different salts are combined, resulting in the formation of insoluble salts that precipitate out of the solution.

One of the best examples of precipitation reactions is the chemical reaction between potassium chloride and silver nitrate, in which solid silver chloride is precipitated out. This is the insoluble salt formed as a product of the precipitation reaction. The chemical equation for this precipitation reaction is provided below.

AgNO₃(aqueous) + KCl(aqueous) — AgCl(precipitate) + KNO₃(aqueous)
In the above reaction, a white precipitate called silver chloride or AgCl is formed which is in the solid-state. This solid silver chloride is insoluble in water. Precipitation reactions help in determining the presence of different ions present in a particular solution.
The other example of a precipitation reaction is the reaction between calcium chloride and potassium hydroxide, resulting in the formation of an insoluble salt Called calcium hydroxide. The chemical equation for this reaction is below-
2KOH(aqueous) + CaCl₂(aqueous) — Ca(OH)₂(aqueous) + 2KCl(aqueous)

Some more examples of chemical equations of on precipitation reaction are as below
AgNO₃(aqueous) + NaCl(aqueous) — AgCl↓ + NaNO₃ (aqueous)
Mg(OH)₂(s) + 2HCl (aqueous) ——— MgCl2(aqueous) + 2H₂O(l)

Properties of Precipitates and Precipitation Reaction

Some of the properties of precipitates and the reaction are as below-

• The precipitation reaction undergoes in aqueous solutions or medium in an ionic state.
• The reaction takes place between ions present in the aqueous solutions, forming the product
• The products formed at the end of precipitation reaction are the precipitates which are insoluble in aqueous solutions
• Precipitation reactions are known as ionic reactions since the ions actively take part in the reaction and form the product.
• These reactions depend on the temperature, concentration of the solution, buffer solution, etc.

Applications of Precipitation Reaction

Precipitation reaction helps in determining a particular element present in the given solution. These reactions also monitor the formation of a precipitate when some chemical is added to solutions. These are used for the extraction of magnesium from the seawater. The human body also encounters these reactions existing between antigens and antibodies.

Examples of Precipitation Reaction In Everyday Life

Precipitation reaction can be used in wastewater treatment. When a contaminant forms an insoluble solid, then we can use this reaction to precipitate out the contaminated ions. In wastewater, a frequent presence of heavy metals can be found such as compounds of sulphide and hydroxide. So, we can add a source of hydroxide that is soluble (NaOH Or Na₂S) that will result in a precipitation reaction.