Solvents are essential in chemistry. They dissolve other substances, forming solutions that are used across research, manufacturing, healthcare, and more.
From cleaning precision components to supporting drug formulation, solvents are behind many everyday products and industrial processes. But what exactly is a solvent, and how does it work?
In this post:
Key Takeaways
A solvent is a substance that dissolves another, forming a solution
Solvents can be liquids, gases, or solids, depending on the application
They’re used across industries, from cleaning and coating to pharmaceuticals
Solvents can be hazardous and should be handled with care
They’re broadly classified as polar, non-polar, organic, or inorganic
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.
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:
- 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
- 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
- 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.
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:
- Sulphur dioxide
- Bromine trifluoride
- Ammonia
- Hydrogen fluoride
- Sulfuric acid
- Hydrogen cyanide
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.
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.
- 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
- 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.
- 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
How Are Solvents Used in Industry?
Solvents play a key role in industrial chemistry. They’re used to dissolve, extract, clean, or carry substances through various processes.
Their ability to break down or dilute other materials makes them ideal for everything from degreasing machinery to coating electronics. Some industries rely on solvents as reaction media; others use them to purify or separate components.
The exact solvent depends on the task. Choosing the right one is critical to safety, efficiency, and final product quality.
Common Industrial Applications for Solvents
In the pharmaceutical industry, solvents are used to manufacture active pharmaceutical ingredients, clean equipment, and extract compounds from natural sources. Their purity and compatibility with drug formulations are tightly regulated.
In paint and coatings, solvents help dissolve binders and pigments, making it easier to apply a smooth, even layer. After you apply a solvent, it evaporates, leaving the finished coating behind.
Manufacturing and engineering sectors use solvents to clean metal parts, remove residues, or prepare surfaces for further treatment. Hydrocarbon and halogenated solvents are common here, depending on the material and required finish.
Food processing and agriculture also make use of solvents, for example, to extract flavours, purify additives, or develop agrochemical formulations. In these cases, food-grade solvents are required to meet safety standards.
Electronics and semiconductors need solvents for cleaning, etching, and degreasing. In high-precision applications, even tiny traces of residue can compromise performance, so highly pure solvents are essential.
Are Solvents Dangerous to Health?
Many solvents are hazardous if not handled correctly. Some are flammable, while others are toxic, corrosive, or harmful to the environment.
Health risks can include skin and eye irritation, dizziness, respiratory issues, and – in the case of prolonged or high-level exposure – organ damage or cancer.
Vapours from volatile solvents can be particularly harmful when inhaled, especially if you’re in an enclosed or poorly ventilated area. Certain halogenated solvents are under restriction or being phased out due to links with long-term health effects and environmental persistence.
To reduce risk, it’s essential to follow proper safety measures. This includes using PPE (such as gloves and eye protection), working in ventilated areas, and using fume extraction systems where appropriate. Regulatory guidance from agencies like the HSE or OSHA should always be followed when working with industrial solvents.
Conclusion
Solvents may seem simple, but they’re fundamental to chemistry and industry. They dissolve, transport, extract, and clean; and the right solvent can determine whether a process succeeds or fails. From pharmaceuticals to electronics, solvents are behind many of the products and systems we rely on every day. But while they’re useful, they also carry risk. Understanding what they are, how they work, and how to use them safely is essential in any scientific or industrial setting.
