A solvent is one which helps other substances (solutes) to get dissolved in it.
Solvents find many applications in formulation of drugs, cosmetics (lipsticks) and also in science and research.
Common solvents include
In science, solvents are useful for chemical analysis by titration, chromatography, spectrometry.
In industry solvents are useful in extraction, purification and also molding of substances into shapes.
There are different type of solvents available and used based upon the need.
Examples of Solvents:
There are many solvents but universal solvent is water. It is least expensive, most commonly used and helps dissolve many substances.
Besides water based on need one can opt for ethanol, oils and petroleum oils like kerosene and petrol.
But for research and industry the list of solvents used include
- Carbon disulphide
- Carbon tetrachloride
- Formic acid
- Acetic Acid
- Trifluoroacetic acid
- Dimethyl sulfoxide
- Dibutyl pthalate
Different types of solvents
Solvents can be briefly classified based on their chemical nature and behavior.
A. Based upon Polarity:
In general most solvents have polarity due to their internal chemistry.
This polarity is due to concentration of charges on one of the element inside a solvent molecule.
It imparts changes on the molecule such that they can dissolve solutes having polarity or able to ionize them.
When a solute is mixed in a solvent, the solvent molecules dissolve the solute by separating apart the solute molecules using forces like hydrogen bonding, vanderwals forces etc.
1. Polar solvents: These are solvents having dielectric constant more than 15. They can dissolve salts and other ionizable solutes. 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 inter-molecular bonds by use of hydrogen bonding, vanderval forces etc. Hence they cannot dissolve polar compounds.Ex: Benzene, CCl4.
Fats and oils are soluble in non-polar solvents. Hence to remove lipids from an extract, petroleum ether is used in industry.
B. Based on Chemical nature:
1. Aprotic solvents: (No protons). These solvents are non reactive and chemically inert. They neither take protons nor give protons. Ex: benzene (C6H6). chloroform (CHCl3).
2. Amphiprotic solvents: Theses solvents which can give and take up protons on reaction. They have neutral pH. Ex: Water, alcohol.
3. Protogenic solvents (proton+genesis = give): These are the solvents acidic in nature. They can donate a proton and hence called “protogenic”. Ex: HCL, H2SO4, perchloric acid.
4. Protophyllic solvents: These are the solvents which take up protons. They are basic in nature and are mostly alkalies. Ex: NaOH, KOH etc.
These protogenic and protphyllic solvents can be again classified as leveling agents and differentiating agents.
A strong acid or base is levelling agents as it can donate or accept protons to even weak base or acid respectively.
While weak acids and weak bases cannot do so and can only give proton to strong base or take up proton from 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 presence of some special elements. Theses special elements bring total change in their physical and chemical properties.
Inorganic solvents: Solvents without carbon are called inorganic solvents. Ex: water, NaOH, HCl
Organic solvents. Solvents having carbon are called organic solvents. Ex: Alcohols (CH3OH), hydrocarbons solvents like Benzene.
Halogenated solvents: Solvents having halogens are called halogenated solvents. Halogens are elements found in 17th group of periodic table.
Based on their behavior and properties, solvents are selected for purposes like acid base titration, complexometry, extraction procedures, solubilisation, chromatography, spectrophotometry etc.
The above nature seems highly specific. Because sugars (C12H22O12) molecules appear to be organic in nature due to 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 also polarity.