Definition of Solvent
Solvent, substance, ordinarily a liquid, in which other materials dissolve to form a solution.
Polar solvents (e.g., water) favor the formation of ions; nonpolar ones (e.g., hydrocarbons) do not. Solvents may be predominantly acidic, predominantly basic, amphoteric (both), or aprotic (neither). Organic compounds used as solvents include aromatic compounds, hydrocarbons, alcohols, esters, ethers, ketones, amines, and nitrated and halogenated hydrocarbons. Their chief uses are as media for chemical synthesis, industrial cleaners, extractive processes, pharmaceuticals, inks, paints, varnishes, and lacquers. Perhaps the most common solvent in everyday life is water. Many other solvents are organic compounds, such as benzene, tetrachloroethylene, or turpentine.
In chemistry, a common rule for determining if a solvent will dissolve a given solute is “like dissolves like.” Solvents composed of polar molecules, such as water, dissolve other polar molecules, such as table salt, while nonpolar solvents, such as gasoline, dissolve nonpolar substances such as wax. The degree that a solvent dissolves a given solute is known as its solubility. Ethyl alcohol is highly soluble in water, for example. Vinegar is very insoluble in oil, and the two substances will quickly separate into two layers even after being shaken well.
Solvent, substance, ordinarily a liquid, in which other materials dissolve to form a solution. Polar solvents (e.g., water) favour formation of ions; nonpolar ones (e.g., hydrocarbons) do not. Solvents may be predominantly acidic, predominantly basic, amphoteric (both), or aprotic (neither). Organic compounds used as solvents include aromatic compounds and other hydrocarbons, alcohols, esters, ethers, ketones, amines, and nitrated and halogenated hydrocarbons. Their chief uses are as media for chemical synthesis, as industrial cleaners, in extractive processes, in pharmaceuticals, in inks, and in paints, varnishes, and lacquers.
Water’s Solvent Properties
- Water, which dissolves many compounds and dissolves more substances than any other liquid, is considered the universal solvent. A polar molecule with partially positive and negative charges, it readily dissolves ions and polar molecules. Therefore, water is referred to as a solvent: a substance capable of dissolving other polar molecules and ionic compounds. The charges associated with these molecules form hydrogen bonds with water, surrounding the particle with water molecules. This is referred to as a sphere of hydration, or a hydration shell, and keeps the particles separated or dispersed in the water.
- When ionic compounds are added to water, individual ions interact with the polar regions of the water molecules during the dissociation process, disrupting their ionic bonds. Dissociation occurs when atoms or groups of atoms break off from molecules and form ions. Consider table salt (NaCl, or sodium chloride): when NaCl crystals are added to water, the molecules of NaCl dissociate into Na+ and Cl– ions, and spheres of hydration form around the ions. The positively charged sodium ion is surrounded by the partially negative charge of the water molecule’s oxygen; the hydrogen’s partially positive charge surrounds the negatively charged chloride ion in the water molecule.
- Since many biomolecules are either polar or charged, water readily dissolves these hydrophilic compounds. Water is a poor solvent, however, for hydrophobic molecules such as lipids. Nonpolar molecules experience hydrophobic interactions in water: the water changes its hydrogen bonding patterns around the hydrophobic molecules to produce a cage-like structure called a clathrate. This change in the hydrogen-bonding pattern of the water solvent causes the system’s overall entropy to greatly decrease as the molecules become more ordered than in liquid water. Thermodynamically, such a large decrease in entropy is not spontaneous, and the hydrophobic molecule will not dissolve.
Applications of Solvent
Solvent products are utilized in almost all manufacturing processes in a wide variety of applications. Many of the products we use that are vital to everyday modern living, such as pharmaceuticals, personal care, or electronics, are all manufactured using solvents in their processes.
With a commitment from the industry to improve the functionality and environmental characteristics of solvent products, new applications are continuously being developed.
The following applications all use solvents in the process of their manufacture :
- Paints and Coatings
- Printing Inks
- Cosmetics and Personal Care
- Food and Beverage
- Cleaning and Degreasing
- Dyes and Pigments
- Chemical Manufacture
Characteristics of the Solvent
- Solvent has the low boiling point and gets easily evaporate.
- Solvent exists as liquid only but can be solid or gaseous as well.
- The commonly used solvents contain the carbon element and hence called as organic solvents, while others are called as inorganic solvents.
- Solvents have characteristic color and odor.
- Acetone, alcohol, gasoline, benzene, and xylene are the commonly used organic solvents and are of great importance in chemical industries.
- Solvents are also used in regulating the temperature in a solution, either to absorb the heat generated during some chemical reaction or to enhance the speed of the reaction with the solute.
Solvents can be broadly classified into two categories: polar and nonpolar. A special case is a mercury, whose solutions are known as amalgams; other metal solutions are liquid at room temperature.
Generally, the dielectric constant of the solvent provides a rough measure of a solvent’s polarity. The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C). Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar.
The dielectric constant measures the solvent’s tendency to partly cancel the field strength of the electric field of a charged particle immersed in it. This reduction is then compared to the field strength of the charged particle in a vacuum.
Heuristically, the dielectric constant of a solvent can be thought of as its ability to reduce the solute’s effective internal charge. Generally, the dielectric constant of a solvent is an acceptable predictor of the solvent’s ability to dissolve common ionic compounds, such as salts.
Polar solvents have large dipole moments(aka “partial charges”); they contain bonds between atoms with very different electronegativities, such as oxygen and hydrogen.
A polar solvent is a type of solvent that has large partial charges or dipole moments. The bonds between the atoms have very different but measurable electronegativities.
A polar solvent can dissolve ions and other polar compounds. It is possible because of the electrical charges pulling on different parts of the solute molecules. The positively charged ions of the solid compound are attracted by the negatively charged side of a solvent molecule and vice versa.
This enables the polar compound to be soluble in the polar solvent. Due to this activity, the ions are evenly distributed throughout the solvent. As for the polarity of the solvent, it basically emerges due to the existing bonds of the atoms with different electronegativity values that lead to the formation of the molecule.
Water is a popular example of a polar solvent. What makes it a polar solvent? If we look at the molecules of water, it has a unique structure with two hydrogen bonds. Further, there is a large difference in the electronegativity between the hydrogen and oxygen atoms.
As such, the large oxygen attracts the electrons close together and gets negatively charged. The hydrogen atoms each get a smaller share of the shared electrons and thus gains a positive charge. This is the very reason for water becoming a very strong dipole molecule.
Non Polar Solvents
Nonpolar solvents contain bonds between atoms with similar electronegativities, such as carbon and hydrogen (think hydrocarbons, such as gasoline). Bonds between atoms with similar electronegativities will lack partial charges; this absence of charge makes these molecules “nonpolar.”
Nonpolar solvents are liquids or solvents that do not have a dipole moment. As a result of this, the solvents are missing any partial positive or negative charges.
Basically, they have small differences in electronegativity. We can also say that the bonds between atoms come with similar electronegativities.
Nonpolar solvents cannot dissolve polar compounds since no opposite charges exist and the polar compound is not attracted. It is this absence of partial charge that also makes these molecules “nonpolar.” Some of the examples of nonpolar solvents include hexane, pentane, toluene, benzene, etc.
Types of Solvents
There are three main types of metal cleaning solutions available for use in precision cleaning :
- Oxygenated Solvents
- Hydrocarbon Solvents
- Halogenated Solvents
Oxygenated solvents. As their name implies, these solvents contain oxygen in their molecular structure. Derived from petroleum products, they typically have low oxicity and high solvent power.
Oxygenated solvents are widely used as additives in manufacturing a huge variety of products, from cosmetics to paint and cleaning.
Many of these applications require a high degree of purity, so specifications for these solvents often focus on levels of impurities, and these products are typically refined to maintain a high level of purity.
However, the manufacturing process for these substances is not expensive, so they tend to be relatively affordable. Examples of oxygenated solvents include alcohols, ethers, esters, glycol ethers, glycol ether, and ketones.
These are petroleum-based solvents whose chemical structure contains hydrogen and carbon atoms. Hydrocarbon solvents can have complex chemical structures. There are two main types of hydrocarbon solvent, including :
These have a straight-chain hydrocarbon structure and are used as metal cleaning solvents as well as in manufacturing. Some examples of aliphatic solvents include gasoline, kerosene and hexane.
Widely used as degreasing agents as well as in the manufacture of paints, inks and agricultural chemicals,these solvents contain a benzene ring structure.
Examples include benzene, xylene and toluene.
The complex composition of hydrocarbon solvents means they can be formulated to fulfill very specific industrial requirements. It is not uncommon for custom hydrocarbon solvents to be created.
Some of the distinguishing factors between different hydrocarbon solvents include flash point, density, distillation range and aroma.
These solvents contain halogen atoms (such as fluorine, bromine, iodine, or chlorine) in their molecular structure.
Because they are typically stable, non-flammable, and fast-evaporating with high solvent capacity, they were widely used in the industry for precision cleaning and many other applications.
However, many types of halogenated solvents have been or are being phased out for environmental reasons. Some examples include perchloroethylene, chlorinated fluorocarbons, and 1,1,1-trichloroethane.