This article aims to provide a brief introduction to a few important concepts in chemistry such as precipitation, combustion, sedimentation, and crystallization. A brief explanation of each of these concepts can be found in the subsections provided below.
Combustion, also referred to as burning, is an exothermic redox reaction that involves the oxidation of a fuel. The meaning of the term ‘combustion’ is a chemical reaction where the oxidizing agent is atmospheric oxygen and the reducing agent is the fuel (which usually contains carbon). The products formed in combustion reactions are usually solid and gaseous in nature (smoke and ash). Although combustion reactions do not always involve the formation of fire, the existence of a fire indicates the occurrence of a combustion reaction. Combustion reactions can be broadly classified into two categories – complete combustion reactions and incomplete combustion reactions.
Complete combustion involves the complete oxidation of the fuel. In such processes, little to no solid byproducts are formed. An example of a complete combustion reaction is the combustion of hydrocarbons such as propane. Incomplete combustion involves the formation of many solid byproducts due to the incomplete combustion of the fuel. Common examples of incomplete combustion include the burning of wood and the burning of coal. The burning of diesel oil is also a great example of incomplete combustion.
The term ‘sedimentation’ is used to refer to the tendency of the particles present in a suspension to settle down at the bottom of their containers. In other words, sedimentation is the settling down of particulate matter in the fluid, after which they come to rest against some barrier (usually the bottom of the container). In the field of chemistry, sedimentation can be used to measure the size of relatively large molecules (commonly referred to as macromolecules). For such measurements, the force of gravity is usually augmented with the help of an ultracentrifuge (which applies centrifugal force on the macromolecule).
Precipitation and rainfall are terms that are often used interchangeably. But what is precipitation? In the field of chemistry, the term ‘precipitation’ is used to refer to the formation of solids from liquids. Precipitation can also occur in chemical reactions. When a chemical reaction occurs in a liquid medium, a solid can be formed which might be insoluble in the liquid environment. This solid is called the precipitate. The process of precipitation is extremely useful for the preparation of pigments. Furthermore, the process of precipitation can also be used to remove salts from water during water treatment. Another vital application of this process is in the field of classical qualitative inorganic analysis.
Crystallization can be defined as the process through which solids are formed (featuring highly organized structural arrangements of atoms, called crystal lattices) from highly concentrated fluids. Some ways through which crystallization occur are listed below.
- Precipitation of crystals from a solution.
- Freezing of a saturated solution to facilitate the formation of crystals.
- Direct deposition onto existing crystals from gaseous media (very rare).
The two steps involved in the process of crystallization are nucleation and crystal growth.