A solvent is a liquid substance that lets other substances get dissolved in it.
Water is a universal solvent and is least expensive and also widely. But there are other solvents preferred based on ethanol, oils, petroleum products, etc.
They find many applications in the formulation of food, drugs, cosmetics (lipsticks), and research.
Common Examples of Solvents include
- Carbon disulfide
- Carbon tetrachloride
- Formic acid
- Acetic Acid
- Trifluoroacetic acid
- Dimethyl sulfoxide
- Dibutyl phthalate
- Petroleum ether
Solvents are chemical compounds that are physically liquids at room temperature. Besides these, even gases can act as solvents when required.
Whereas in the industry, these solvents are mainly used for the extraction, purification, and molding of substances into different shapes.
There are different types of solvents that are routinely used.
Different types of solvents
Solvents can be classified based on their chemical nature and behavior.
A. Based upon Polarity
In general, most solvents have polarity in their internal chemistry.
This polarity is due to the concentration of opposite charges on one of the atoms or elements inside a solvent molecule.
It imparts changes to the solute molecule structure such that they get dissolved by forming ions.
When a solute is mixed in a solvent, the solvent molecules dissolve the solute by separating the solute molecules using forces like hydrogen bonding, Vanderwal forces, etc.
Examples: Sodium chloride has a NaCl molecule, which breaks into Na+ and Cl- ions when dissolved in water.
1. Polar solvents
These are solvents having a dielectric constant of more than 15. They can dissolve salts and other ionizable solutes.
Polar solvents Ex: water, alcohol. Polar solutes like salts dissolve in polar solvents.
2. Non-polar solvents.
These solvents are non-polar and have dielectric constants less than 15. They cannot form intermolecular bonds by use of hydrogen bonding, Vanderwal forces, etc. Hence they cannot dissolve polar compounds.
Nonpolar solvents Ex: Benzene, CCl4.
Fats and oils are soluble in non-polar solvents. Hence to remove lipids from an extract, petroleum ether is used in the industry.
B. Based on Chemical nature:
1. Aprotic solvents (No protons).
These solvents are nonreactive and chemically inert. They neither take protons nor give protons.
Ex: benzene (C6H6). Chloroform (CHCl3).
2. Amphiprotic type
These solvents can provide and take up protons on reaction. They have a neutral pH.
Ex: Water, alcohol.
3. Protogenic type (proton+genesis = give)
These are the solvents acidic by nature. They can donate a proton and hence called “protogenic.”
Ex: HCL, H2SO4, perchloric acid.
4. Protophyllic type
These are the solvents that take up protons. They are basic by nature and are mostly alkalies.
Ex: NaOH, KOH, etc.
These and protophilic solvents can be again classified as leveling agents and differentiating agents.
A strong acid or base is a leveling agent as it can donate or accept protons to even weak base or acid, respectively.
While weak acids and weak bases cannot do so, they can only give proton to a strong base or take up a proton from a strong acid, respectively. Hence due to this differentiation, they are called differentiating agents.
C) Based on chemistry
Solvents are also classified based on their center of chemistry due to the presence of some particular elements. These unique elements in solvents bring a total change in their physical and chemical properties.
a) Inorganic solvents: Liquids without carbon in their chemistry are called inorganic solvents.
Ex: water, NaOH, HCl
b) Organic solvents. Those liquids having carbon are called organic solvents.
Ex: Alcohols (CH3OH), hydrocarbons like Benzene.
c) Halogenated solvents:
Liquids having halogens are called halogenated solvents. Halogens are elements found in the 17th group of the periodic table.
d) Deuterated solvents:
These have deuterium, a hydrogen isotope, in their molecular structure. They are preferred in experiments where hydrogen has to be avoided. For example, in nuclear magnetic spectroscopy, the solvents with hydrogen can interfere in the analysis. Hence, solvents substituted with deuterium instead of the hydrogen atom are preferred.
Their examples include Deuterated form of water (D2O), methanol (CD3OD), acetic acid (CD3COOD), trifluoroacetic acid (CF3COOD), etc.
The above nature seems highly specific. Because, sugar (C12H22O12) molecules are organic by nature due to the presence of carbon in it.
But interestingly, sugar is insoluble in organic solvents like benzene. This is because sugar molecules have polarity and require polar solvents to dissolve.
Hence we see sugar dissolves well in plain water, which is inorganic but having polarity.
So among the types of solvents available, to dissolve a solute, one should consider both chemistry and polarity.
D) Based on Physical property
a) Volatile type: These are the volatile liquids and evaporate as gas at around room temperature due to low boiling points. They can be stored in ambered colored containers with tight closure. But, once they are kept open, the liquid starts evaporating and over a period of time, like in hours, the container gets empty.
If the liquid has an aroma, it can be felt all over the room if the lid is kept open.
Examples: Diethyl ether (B.P= 34.5 degree centigrade)
b) Non-Volatile type: Most of the solvents come under this category. They have high boiling points and hence are stable at room temperature. They get evaporated when heated to higher temperatures depending on their boiling points.
Examples: Water (B.P= 100 degrees), ethanol (B.P=78 degrees).
c) High-density type: These liquids have high density and can be called as heavy liquids. Due to this, their weight per volume is higher than those with low density.
Examples: Chloroform has a density of 1.49 g/cm³.
d) Low-density type: These liquids have low density due to which their weight per volume is lower.
Examples: petroleum ether has a density of 0.64 g/cm3.