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Solvent

What is a solvent?

A solvent in chemistry is a chemical substance in which other types of materials dissolve to form a solution. It is the major component of a chemical solution. Commonly, solvents are liquid but they may also exist as a solid, gas, or supercritical fluid.

Solvent definition and types in chemistry, examples of common solvents solute and chemical solution

The solvent is broadly classified into two types polar and non-polar. Most common examples of liquid solvents may include water, ammonia, benzene, ethanol, methanol, acetone, etc. These inorganic and organic solvents are used to dissolve the solutes to form a homogeneous mixture.

Water is the most common polar solvent which we used for dissolving various types of chemical substances and organic molecules such as ions and proteins present in a cell.

The solvent may be toxic or non-toxic in nature. Water and benzene are commonly used solvents in many industrial and household products due to their low toxicity.  In recent years, the green chemistry movement used to design, develop, and implementation of non-toxic and sustainable chemical solvents.

Non aqueous solution

A non-aqueous solution is a solution in which the solvent is any liquid other than water. Ammonia, hydrogen fluoride, sulfuric acid, and hydrogen cyanide are common examples of protic nonaqueous solvents. Prominent members of aprotic nonaqueous solvents are sulfur dioxide, sulfuryl chloride, dinitrogen tetroxide, antimony trichloride, and bromine trifluoride.

Types of solvent

Different types of solvents may be classified in a number of ways depending on their physical and chemical properties. Commonly, solvents are classified into two categories,

  1. Ionizing (polar or ionic) solvents
  2. Non-ionizing (non-polar or non-ionic) solvents

The dielectric constant of the solvent provides the rough measurement of solvent polarity.

  • For example, strong polar solvents like water, ammonia, hydrogen fluoride, and sulfur dioxide have very high dielectric constant.
  • While non-polar solvents like benzene and carbon tetrachloride have a very low dielectric constant (less than 15).

Polar solvents

Ionizing solvents are polar or ionic in nature. Hence, they can dissolve ionic compounds and initiate ionic reactions. Polar solvents exist as ions in their pure state. Therefore, they are the weak conductors of electricity. These types of solvents have a high value of dielectric constants and a strong tendency to form associated structures.

Many polar solvents like water, alcohols, and other hydroxyl-containing substances such as acetic acid have the ability to form hydrogen bonding with solute molecules.

A polar solvent has a tendency to participate in self-ionization reactions. The self-ionization reaction of water, ammonia, and sulfur dioxide are,
H2O + H2O → H3O+ + OH
NH3 + NH3 → NH4+ + NH2
SO2 + SO2 → SO+2 + SO3−2

Non-polar solvents

Non-polar solvents are non-ionic in nature. Therefore, they can dissolve only natural or non-polar compounds and do not initiate ionic reactions.

Non-polar solvents have low dielectric constants. They have very little associating and solvating tendency between solvents and solute. Common examples of non-polar solvents are organic hydrocarbons, benzene, toluene, carbon tetrachloride, etc.

On the basis of proton donner and proton acceptor properties, the solvents may be classified in three ways,

  1. Protic solvent
  2. Aprotic or non-protic solvent
  3. Amphoteric solvent

Protic solvent

A protic solvent has a hydrogen atom in its formula. In other words, it is a solvent that contains a labile H+ ion. They have the ability to form hydrogen bonding. These solvents are of two types, acidic or photogenic and basic or protophilic solvents.

  • Acidic or protogenic solvents have a strong tendency to donate protons. Examples of such solvents are sulfuric acid, hydrogen fluoride, hydrogen cyanide, etc.
  • Basic or protophilic solvents have a strong tendency to accept protons. Ammonia, amines, and hydrazine are belongs to such classes.

Aprotic solvent

The solvent that neither donate nor accept protons is called an aprotic solvent. They may or may not have hydrogen atoms in their formula. Benzene, chloroform, sulfur dioxide, and carbon tetrachloride are examples of aprotic solvents.

Amphoteric solvent

An amphoteric solvent contains hydrogen in its formula and it donates or accepts protons depending on the nature of reacting species. It acts as an acid and base. Therefore, it is amphoteric in nature.

These types of solvents dissociate freely into protons and anions. Common examples of amphoteric solvents are acetic acid and water.

Properties

The general properties of solvents depend mainly on

  • Dipole moment: Solvent having a higher value of dipole moment dissolve polar substances more readily. The greater polarity of a solvent molecule releases greater solvation energy on the dissociation of a solute.
  • Dielectric constant: The dielectric constant provides a rough measurement of solvent polarity. The strong polarity of water may be indicated by its high dielectric constant of 88.
  • Electrical conductance: Electrical conductance gives an idea about the self-ionizing properties of a solvent.
  • Viscosity: Viscosity is an important property of a liquid solvent. Some solvents like water, low molecular weight alcohols, and liquid ammonia are highly fluid while anhydrous sulfuric acid and high molecular weight alcohols are highly viscous. Liquid with low viscosity can handle more easily than high viscous liquid.
  • Proton affinity: It is applicable for a protonic solvent only. It greatly affects the behavior of a solute in a given solvent system. Ammonia has a greater proton affinity than water molecules. Acetamide behaves as a very weak base in an aqueous solution but it shows acid properties in liquid ammonia.

Examples of solvent

Some common examples of solvents with their properties are listed below the table,

Solvent Chemical formula Boiling point (°C) Density (g/mL) Dielectric constant
Dipole moment (D)
Nonpolar solvent
Pentane CH3CH2CH2CH2CH3 36.1 0.626 1.84 0.00
Hexane CH3CH2CH2CH2CH2CH3 69 0.655 1.88 0.00
Benzene C6H6 80.1 0.879 2.30 0.00
Toluene C6H5-CH3 111 0.867 2.38 0.36
1,4-Dioxane C4H8O2 101.1 1.033 2.30 0.45
Diethyl ether CH3CH2-O-CH2CH3 34.6 0.713 4.30 1.15
Tetrahydrofuran C4H8O 66 0.886 7.5 1.75
Chloroform CHCl3 61.2 1.498 4.81 1.04
Polar protic solvent
Ammonia NH3 -33.3 0.674 17 1.42
Formic acid H-C(=O)OH 100.8 1.21 58 1.41
n-Butanol CH3CH2CH2CH2OH 117.7 0.810 18 1.63
Isopropyl alcohol (IPA) CH3-CH(-OH)-CH3 97 0.803 18 1.68
n-Propanol CH3CH2CH2OH 97 0.803 20 1.68
Ethanol CH3CH2OH 78.2 0.789 24.55 1.69
Methanol CH3OH 64.7 0.791 33 1.70
Acetic acid CH3COOH 118 1.049 6.2 1.74
Water H2O 100 1.00 80 1.85
Polar aprotic solvent
Dichloromethane (DCM) CH2Cl2 39.6 1.3266 9.1 1.60
Ethyl acetate CH3-C(=O)-O-CH2-CH3 77.1 0.894 6.02 1.78
Acetone CH3COCH3 56.1 0.786 21 2.88
Dimethylformamide (DMF) H-C(=O)N(CH3)2 153 0.944 38 3.82
Acetonitrile CH3-C≡N 82 0.786 37.5 3.92
Dimethyl sulfoxide (DMSO) CH3-S(=O)-CH3 189 1.092 46.7 3.96
Nitromethane CH3-NO2 100 1.1371 35.87 3.56
Propylene carbonate C4H6O3 240 1.205 64.0 4.9

A solvent is a chemical that uses,

  • For dissolving paint, oil, and gases.
  • Mix or thin pigments, pesticides, glues, epoxy resins, and paints.
  • To clean automotive parts, tools, and electronics.
  • To make other chemicals.

Therefore, a solvent is broadly defined as a liquid or gas which uses for dissolving or extracting other substances in chemical industries.