Solvent: What it Is, What You Need to Know

In this article:

• What is a Solvent?
• Types of Solvents
• What Does a Solvent Do?
• How to Choose a Solvent
• Properties of Solvents
• Examples of Solvents

What is a Solvent?

A solvent is, by definition, any substance that will take other things (aka ‘solutes’) into solution.

For example, in a saltwater mixture, water functions as the solvent, and salt is the solute. Besides water, a lot of different families of organic products can function as solvents. There are alcohol solvents, ketone solvents, aliphatic & aromatic solvents, glycol ethers, and others. Some of these bad smelling, crude-derived solvents (such as Acetone) may be what you typically think of when you think of solvents. One important thing to know is that, in the case of a solvent/solute solution, the solute can always be returned to its pre-dissolved state. Acids are not solvents, because they digest materials, rather than dissolve them. The material can’t be retrieved later. Conversely, in the case of salt and water, if the water evaporates, the salt remains.

If something is ‘insoluble’, that means that it’s not possible to dissolve it into a solution (i.e. Sand will never dissolve into water and is an insoluble substance).

What makes up a solvent? Lots of things can– it varies from family to family. Ultimately, a solvent is made up of its molecular structure.

Disassociation: An interesting phenomenon called ‘disassociation’ happens in a solvent solution. To use our saltwater example, when the sodium chloride (NaCl) molecule dissolves in the water, it comes apart. The ‘Na’ (sodium) molecule and the ‘Cl’ (chlorine) molecule let go of each other and swim freely around in the water solution. Then, when the water evaporates, they come back together again.

Types of Solvents

There are various types of solvents, and it helps to have a basic understanding of some of the terms used to describe them:

Organic / Inorganic: The word ‘organic’ once meant ‘from life’. In modern chemistry, it means ‘contains carbon’. (Keep in mind that all living things contain carbon!) Inorganic simply means that it doesn’t contain carbon. Water, for example, is made up of hydrogen and oxygen, so it is inorganic. Organic solvents are typically derived from crude oil.

Polar / Nonpolar: All elements are either positively or negatively charged. Known as cations and anions, this is basically how things stick together (like magnets). Molecules are usually made up of an equal number of positive and negatively charged elements. Polar molecules have positively charged and negatively charged poles on different sides of the molecule, and the molecule’s overall charge is not balanced in the middle. In nonpolar solvents, the molecule’s charge is balanced in the middle. The polarity of solvents is helpful to know because polar solvents tend to dissolve polar compounds best, and nonpolar solvents tend to dissolve non-polar compounds best.

Water is a polar solvent and is considered ‘the universal solvent’ because it can take both semi-organic and aqueous things into solution. It is the only solvent that can.

What Does a Solvent Do?

The role of a solvent is to dissolve the solute and create a solution. This solution can be used in various ways:

Sometimes, the goal is to have the solution itself for use.

Other times, such as in paints & coatings applications, the goal of the solvent is to carry the solute to where it’s needed. Then, the solvent evaporates, leaving behind the coating of paint or adhesive. Paints are a common use for solvents, as they are made up of resins and dispersants (solutes) that must be kept fluid and in solution until applied to the surface they’re covering. Adhesives are another common application. When the carrier solvent evaporates, the adhesives begin to set up and harden (i.e. adhesives used in construction).

What is a solvent cleaner? Lots of solvents are used for cleaning applications. The term ‘solvent cleaner’ is typically used to refer to cleaners made from organic products (i.e. alcohols, acetates, etc.), that may be bought in the ‘Paints & Coatings’ section of your local hardware store. However, a water-based cleaner technically can be a (water-based) solvent cleaner, also.

How to Choose a Solvent

Choosing the best solvent for your application may take some education, and possibly a little trial and error. (Note: It is important to have an understanding of the materials and hazards involved before you attempt the ‘trial and error’ process!)

For most non-disinfecting cleaning applications, it is generally best to start with water-based cleaners, as they are easier to use, friendlier on the environment, and less hazardous.

For a true organic solvent application: if, for example, you are trying to clean up an adhesive residue, a good starting point is to look at the label on the adhesive. Find out what solvent was in it to begin with. Was it Isopropyl Alcohol? Toluene? There is a chance that if you use this solvent to clean the residue off, it will work. However, keep in mind that it doesn’t always work, since adhesives go through a reaction process when they dry.

For more help on choosing the best solvent for your industrial application, reach out to a representative!

Properties of Solvents

The larger the solvent molecules are, typically the higher the flash point, the higher the boiling point, and the slower the evaporation rate.

In order to evaporate, there has to be enough energy in the molecule for it to break free of the other molecules it’s connected to. The smaller the molecule, the easier it is to break free. If the molecule is longer / more complex, it takes more energy (or, a greater amount of heat), to break free. Do all solvents evaporate? To our knowledge, the answer is yes. As long as they have a vapor pressure, given the right conditions, they will all always evaporate- although some may do so so slowly, it’s not noticeable, even in a lifetime. Organic solvents tend to evaporate much faster than aqueous solutions. Different families of organic solvents have a tendency to evaporate faster.

Can a solvent be a solid? No. While some can exist as a solid, by default, a solid product cannot be a solvent.

Kaributanol (Kb) Value: The Kaributanol, or Kb, Value indicates a solvents strength or ability to pull things into solutions. It’s listed on a product’s SDS. A stronger Kb value doesn’t mean it can pull everything into solution, however. It just means that it has a greater likelihood it will pull things into solution. Some solvents that have high Kb values, may not work at all in certain situations. Conversely, a solvent with a lower Kb value and different chemical makeup may work perfectly. This has to do with the chemistry of the solvents.

Examples of Solvents