What Is a Solvent in Science?

A solvent is a substance that is proportionally greater by volume or mass than the substance it dissolves, which is called the solute. 

Solvents can be a gas, a liquid, a supercritical fluid, or even a solid substance. A combination of solvent and dissolved solute is a homogeneous mixture known as a solution. Many industrial processes require one or more types of solvents at various stages of processing.

What Does Solvent Mean?

Many people think of a liquid when the term solvent is mentioned. However, a solvent can also be a gas, a supercritical fluid, or a solid substance. It’s also possible for a solvent to become a solute and a solute to become a solvent. The main difference between a solute and a solvent is the molar proportions of the two substances.

A solvent, by definition, is proportionally greater than the solute it dissolves. A solute spreads almost evenly throughout the solvent to form a solution. When the solvent dissolves the solute, the two become indistinguishable, making them a homogeneous mixture.

The solute cannot easily be separated from the solvent, even by simply waiting for the former to precipitate. Special processes are necessary to separate the solute from the solvent, requiring more energy. For instance, if a solute is a solid, like table salt, and the solvent is a liquid,like water, the liquid solvent must be evaporated in order to extract the solute.

Unlike a chemical reaction, the solute and solvent do not necessarily form new substances. Ions may form in a solution, but the process is completely reversible. No new and permanent rearrangements of atomic bonds are formed. The process is also reversible.

To understand the role of a solvent in forming various types of solutions, refer to the table below. Remember that a solvent can also function as a solute, depending on the relative proportions.

As you can see from the table, the solution usually takes the form of the solvent, but there are some exceptions. For example, an amalgam of mercury in silver or gold is a liquid solvent but the solution is in the form of solid gold.

What Types of Solvents Are There?

Water is considered to be a universal solvent because it can dissolve a wide range of substances, including solids, liquids, and gases. However, there are many other substances that water cannot dissolve, such as hydrocarbons. Many other examples of solvents exist, but in general, they can be classified into three basic categories:

  1. Polar protic solvents

Solvents that belong to this category generally have a polar hydroxyl (-OH) group and a nonpolar tail. Therefore, the chemical formula can be generalised as R-OH. The structure of these solvents allows them to dissolve substances with similar molecular structures. They’re miscible with water, a.k.a. hydrophilic, forming homogeneous mixtures. Some examples of these solvents are the following:

  • Water: H-OH
  • Acetic acid: CH3CO-OH
  • Methanol: CH3OH
  • Ethanol: CH3CH2-OH
  • n-Propanol: CH3CH2CH2-OH
  • n-Butanol: CH3CH2CH2CH2-OH
  1. Dipolar aprotic solvents

The molecules of these solvents have highly polar chemical bonds as well as large bond dipole moments. Some examples of these solvents include the following:

  • Acetone: (CH3)2C=O
  • Ethyl acetate: CH3CO2CH2CH3
  • Dimethyl sulfoxide: (CH3)2SO
  • Acetonitrile: CH3CN
  • Dimethylformamide: (CH3)2NC(O)H
  1. Non-polar solvents

These solvents have a neutral net charge because of the way the electric charges are evenly distributed. As a result, their molecules are hydrophobic, which means that they cannot mix with water. Their dielectric constant is very low. They can dissolve nonpolar substances, such as fats and grease. Some examples of these solvents are the following:

  • Carbon tetrachloride: CCl4
  • Benzene: C6H6
  • Diethyl ether: CH3CH2OCH2CH3
  • Hexane: CH3(CH2)4CH3
  • Methylene chloride: CH2Cl2

Many of these solvents can be combined with others to form more powerful solvents that are used for various industrial purposes.

Scientist wearing blue gloves holding Erlenmeyer Conical flask, with purple violet solvent inside

What Are Industrial Solvents?

Industrial solvents are either single-substance solvents or multi-component solvents. They’re used as cleaning agents and as precursors or reagents for manufacturing various products. Handling these solvents requires extra precaution, such as wearing PPE, because they’re hazardous substances; some are flammable while others are corrosive, and a few of them are also carcinogenic.

Many industrial solvents are organic solvents that are used for cleaning metals and machineries. They’re also used as chemical precursors, reagents, and catalysts in many manufacturing processes. They’re all hazardous, but at varying degrees of toxicity. These solvents can irritate the skin, the mucous membranes of the lungs and eyes, and may cause serious illness when ingested. Here are the three classifications of industrial solvents based on their compositions.

  1. Oxygenated solvents

These solvents have oxygen as part of their molecular structure. They’re commonly derived from fossil fuels and have relatively low toxicity compared to other types of industrial solvents. They have a wide range of applications, such as in manufacturing cosmetics and paint.

A high degree of purity is necessary for these solvents to be effective in their various applications; any impurities can ruin the final products. Refining processes are done to ensure high levels of purity. Manufacturing these solvents is relatively affordable and simple.

Examples of these solvents are the following:

  • Alcohols
  • Ethers
  • Esters
  • Glycol ethers
  • Glycol ether esters
  • Ketones
  1. Hydrocarbon solvents

These solvents are derived from crude oil or fossil fuels. As the name suggests, they only contain hydrogen and carbon. They vary in complexity of molecular structures and number of chains. Their two main categories are the following:

  • Aliphatic hydrocarbons: Straight-chain solvents that are mainly used for cleaning metals. Examples include gasoline and kerosene
  • Aromatic hydrocarbons: These solvents contain a benzene ring structure. They’re used as degreasing agents, as components of paints, and in agricultural chemicals such as pesticides. Some examples of these solvents are benzene and xylene.
  1. Halogenated solvents

These solvents contain halogen atoms such as fluorine, bromine, iodine or chlorine. Unlike the other two categories of industrial solvents, halogenated solvents are not flammable. They’re commonly used for precision cleaning. Some of them are now being phased out because of their environmental impacts. Examples include:

  • Perchloroethylene
  • Chlorinated fluorocarbons
  • 1,1,1-trichloroethane
Common organic solvents and their chemical structures

What Are Organic and Inorganic Solvents?

The main distinction between organic and inorganic solvents is the presence or absence of carbon in their composition: organic solvents have carbons in them, while inorganic solvents do not. Water is the most abundant inorganic solvent. Other examples of inorganic solvents are the following:

These solvents are either protic or aprotic solvents. They have a wide range of applications in industries and chemical research. They’re used in reactions that cannot occur in aqueous solutions or reactions that require a special environment.

Want to find out more about solvents? Take a look at this article: What Is The Role Of A Solvent In A Chemical Reaction?

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