Dissolving one substance into another and observing the consequent physical or chemical changes is one of the most common practices in chemistry. These changes are a result of interactions of forces among the molecules of different substances. Sometimes these interactions can result in the ionization of a solute when dissolved in a particular solvent. The substances that can dissociate into ions on dissolving in a polar solvent are known as electrolytes; however, the substances that do not yield ions on dissolution are known as non-electrolytes. Whether a solution contains a non-electrolyte or an electrolyte solute can be determined by immersing two electrodes in the solution and applying an electric potential across them. To conduct electricity, a substance must contain freely mobile, charged species. Due to the presence of ions in an electrolyte solution, it can conduct electricity, whereas, in the case of non-electrolytes, conduction is not possible due to the absence of any charge carriers. Let’s discuss a few of the examples that form non-electrolytes that one can come across in daily life.
1. Sugar
Sugar is the generic name given to a sweet-tasting carbohydrate that adds flavor to our food and can be commonly found in our kitchens. In chemistry, sugars are classified into two types: simple sugars, also known as monosaccharides, which include glucose, fructose, and galactose, and compound sugars, also known as disaccharides, which include two monosaccharides joined by a glycosidic bond. When we dissolve sugar in a polar solvent such as water, it completely dissolves, just like salt; however, unlike saltwater, a sugar solution can not conduct electricity through it and is thus classified as a nonelectrolyte.
2. Alcohol
Ethanol, also known as ethyl alcohol, is an organic covalent hydrocarbon compound with the chemical formula {CH}_{3}{CH}_{2}{OH}. Most of us are familiar with a diluted solution of ethyl alcohol commonly sold by the name “liquor” in the market. When diluted with water, ethyl alcohol molecules get evenly surrounded by the water molecules; however, they do not dissociate into ions like salt because of covalent bonding. It is important to note that this is the case with most but not all covalent compounds. Organic acids such as carboxylic acid ({CH}_{3}{COOH}), formic acid ({HCOOH}), etc., can dissociate into corresponding ions, and therefore, these are classified as electrolytes.
3. Benzene
Benzene is a cyclic and aromatic hydrocarbon chemical with the chemical formula {C}_{6}{H}_{6}. We might not encounter pure benzene in our daily life experiences, but it is one of the most common ingredients in several polymer materials, such as plastics, resins, nylon, and synthetic fibers. Benzene is also used to make some types of lubricants, rubbers, dyes, detergents, drugs, and pesticides. The basic chemistry of benzene tells us that it is a nonpolar compound, and therefore, it does not dissolve in polar solvents. Nonetheless, several studies have shown that water, at supercritical temperature and pressure conditions, can effectively dissolve up to few grams of benzene. During the dissolution of benzene in supercritical water, the intermolecular bonds break and the benzene molecules get dissociated; however, the intramolecular bonds between hydrogen and carbon atoms of benzene remain intact, and hence, no ionization takes place. In other words, benzene is also a non-electrolyte that does not conduct electricity when dissolved in water.
4. Cholorform
Chloroform, also known as trichloromethane, is a colorless and pungent-smelling liquid organic compound with the chemical formula {CHCl}_{3}. Most of us are familiar with this chemical due to its dramatic representation as a chemical used to instantly knock out a person; however, in reality, it takes at least 5-7 minutes of inhaling chloroform to show any anesthetic effects. Chloroform is the main ingredient in the preparation of PTFE (Teflon), a chemical that can commonly be found as an integument on non-stick pans. The molecular structure of trichloromethane implies that the electric charge is unevenly distributed over the molecule, and therefore, it acts as a non-polar compound and does not separate in polar solvents like hydrochloric acid (HCL). When dissolved in water, chloroform slightly dissociates into individual molecules rather than dissociating into ions; therefore, it is also a non-electrolyte.
5. Naphthalene
Naphthalene is a white crystalline volatile solid with the chemical formula {C}_{10}{H}_{8} and a distinctively strong odor. It is best known for being the main ingredient in mothballs. At room temperature, it sublimes directly from solid to vapor state, which is why the mothballs we put in our clothes get shrunk in size over time without leaving any residue. The chemical structure of naphthalene is composed of ten carbon atoms and eight hydrogen atoms, and it can be viewed as two benzene rings fused together, sharing two of the eight carbon atoms. This structure allows naphthalene to have three resonance structures; however, all these structures have zero dipole moment. The nonpolar nature of naphthalene does not allow it to dissolve in polar solvents like water; and therefore, like benzene, naphthalene is also a nonelectrolyte as it cannot dissociate into ions when dissolved in water.
6. Toluene
Toluene is an aromatic hydrocarbon compound with the chemical formula {C}_{6}{H}_{5}{CH}_{3}. The chemical structure of toluene comprises a methyl group ({—CH}_{3}) attached to a benzene ring, replacing one of the six hydrogen atoms. It is a major ingredient in the production of paint thinners, white-board/permanent markers, contact cement. and certain types of glues. Toluene does not dissolve in water. It forms an emulsion with water because of its nonpolar nature, which makes it inefficient in breaking the polar bonds between hydrogen and oxygen atoms of the water molecules. For the same reason, toluene falls under the category of non-electrolytes as it can not dissolve or dissociate into ions when dissolved in polar solvents like water.
7. Acetone
Acetone, a common name for propanone, is an organic compound, belonging to the category ketones, with the chemical formula ({CH}_{3})_{2}{CO}. It is a colorless, highly volatile, and flammable liquid with a characteristic pungent odor. Unlike previously discussed examples, acetone is a polar substance due to the presence of the carbonyl group that provides it with the dipole moment; and therefore, it can dissolve in water, a polar solvent. The negative charge present on the oxygen atom of acetone can attract the partially positive hydrogen atom of the water molecule, forming a hydrogen bond. It is important to note that when we dissolve acetone in water, molecules of acetone do not dissociate into ions; however, they get thoroughly mixed to form a heterogeneous mixture. Acetone can commonly be found in several household items such as nail polish removers, wet wipes, hair colors, paint thinners, etc.
8. Carbon tetrachloride
Carbon tetrachloride, also known as tetrachloromethane, is an organic compound with the chemical formula {CCl}_{4}. Since it contains a carbon atom that is connected to more than one halide functional group, it is often known as a polyhalogenated organic compound. {CCl}_{4} is a colorless liquid with a very sweet odor under normal temperature and pressure conditions. It can commonly be found in several household items, such as propellant in aerosol cans (perfumes and insecticides), cleaning agents, a refrigerant, and in lava lamps. Although a bond between carbon and the chlorine atom is polar in nature, the molecule {CCl}_{4}is non-polar because the polarities of all the C-Cl bonds are in opposite direction, which cancels out and results in zero dipole moment of the molecule. Being non-polar, carbon tetrachloride does not dissolve in polar solvents, and therefore, it is a non-electrolyte.