What Is The Role Of A Solvent In A Chemical Reaction?

Chemical reactions involve the breaking and the joining of atomic bonds (ionic, covalent, polar, and hydrogen bonds) in which the role of a solvent is crucial. 

About Atomic Bonds

  • Ionic bond – using the transfer of an electron between atoms
  • Covalent bond – sharing electrons between atoms (the most common type of atomic bond)
  • Polar bond – where different atoms exert different attractions for the electrons
  • Hydrogen bond – where a hydrogen atom is situated between two other atoms that have a high affinity for electrons

The process of chemical reactions produces new compounds and releases or absorbs heat. It may also liberate some elements. For instance, the chemical reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) is an exothermic reaction. It produces two by-products, namely, water (H2O) and table salt (NaCl). In scientific experiments, you will need specific molar concentrations of the two chemicals in water as a solvent to balance the reaction.

What Is A Solvent In Chemistry? 

A solvent can be an organic or inorganic liquid, gas or solid that dissolves a solute, or minor component, in a solution. It is proportionally greater in amount than the solute.

Similar to catalysts, some solvents do not participate in chemical reactions. They simply serve as the reaction medium to enable chemical reactions to occur more rapidly.

A solution is formed when a solute dissolves in a solvent

The Main Types Of Solvents

The role of a solvent in a chemical reaction can either be non-participatory or participatory. It all depends on the type of solvent and its strength. Solvents are classified as either inorganic or organic.

Inorganic solvents

Inorganic solvents are solvents that do not have carbon in their chemical compositions. Water is the most common example of an inorganic solvent.

Common acids such as hydrochloric acid and sulphuric acid are also examples of inorganic solvents. These are polar solvents that dissolve substances by breaking the molecular bonds of polar or ionic molecules of solutes. They may also directly react with solutes, forming new compounds.

Organic solvents

Organic solvents are those that contain carbon in their chemical makeup. Some are polar solvents but some are non-polar ones. Organic solvents are classified into three categories based on their chemical structure.

  • Hydrocarbon solvents – these contain only hydrogen and carbon chains or rings. Examples are kerosene and benzene.
  • Oxygenated solvents – these solvents have either double-bonded oxygen or an oxygen attached to a hydrogen and hydrocarbon chain. Examples include alcohols, ketones, aldehydes, glycol ethers, esters, glycol ether esters.
  • Halogenated solvents – these solvents have hydrocarbons attached to elements from the halogen group, namely, fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). Examples of these solvents include chlorinated and brominated hydrocarbons.

Why Is Water A Good Solvent?

Sometimes playfully referred to a dihydrogen monoxide, the most abundant and active solvent in the world is water, specifically the ocean. Ocean water covers about 71% of the earth’s surface area. About 97.5% of water on earth is saltwater; 2.5% is freshwater but only 0.3% is in liquid form on the surface.

Ocean water is a solvent that covers 71% of the earth

The ocean has a variety of dissolved salts. About 3.5% of seawater is salt by weight. Hence, a cubic kilometre of seawater has about 35 tonnes of salt.

Water can dissolve a wide range of substances, not only salts, because of its polar molecular structure. The hydrogen atoms in a water molecule have a bond angle of 104.5°. This means that one side of the molecule is slightly positive and the other is slightly negative.

Water can dissolve virtually all types of ionic and polar compounds. These include many organic molecules such as amino acids and DNA. Other organic molecules such as vitamin E are non-polar. Hence, they are not soluble in water but as a rule of thumb, an organic molecule is water soluble if the ratio of carbon atoms to oxygen atoms is equal or less than five, C/O≤5.

Water As The Solvent Of Life

Life as we know it will not exist without the polarity of water. The theory of abiogenesis – that pre-cellular life once existed on earth – put emphasis on the crucial role of water as solvent. For instance, it was experimentally demonstrated by the Urey-Miller experiment in 1952 that amino acids can be synthesised by simulating the pre-biotic conditions of ancient earth.

Water is essential to life on earth because it carries nutrients and minerals. It serves as a medium of chemical reactions and also as structural support for cells.

It has a central role in both metabolism and structural integrity of the cells. Most biochemical reactions in an organism will not occur without water as a solvent.

Therefore, it’s not surprising that organisms have high water content. The adult human body, for instance, is about 60% water.

On average, a human can survive for up to a month without food but will probably die in three days without water. Other factors such as age, health, and activity levels can affect the longevity of a person without drinking water.

What Are Non-Aqueous Solvents?

Aqueous solutions contain water as their solvent. When written as chemical equations, these solutions are appended with (aq) in their chemical formula to indicate that water is used as solvent. For example, a solution of table salt is written as Na+(aq) + Cl−(aq). Vice versa, a non-aqueous solution is a liquid solution that does not have water as a solvent.

Non-aqueous solutions can either be polar or non-polar, organic or inorganic. Non-aqueous solutions include alcohol solutions, ether solutions, and hydrocarbon solutions. Liquid ammonia is one of the most widely studied non-aqueous ionising solvents. It can dissolve metals, resulting in coloured and electrically conductive solutions.

Many non-aqueous solutions have industrial, household, and medical applications. Tincture of iodine, for instance, is a non-aqueous solution with alcohol as its solvent. Meanwhile, some paint products are oil-based, which can be dissolved in thinners like acetone.

Other non-aqueous solutions use aromatic hydrocarbons such as toluene in the manufacture of inks, insecticides, and agricultural chemicals.

Is Nail Polish Remover A Solvent?

One of the most common non-aqueous solvents used for cosmetic and beauty purposes is nail polish remover. Acetone is the most common type of nail polish remover. It is the simplest and smallest type of ketone with the chemical formula (CH3)2CO.

Nail polish remover contains acetone - a strong solvent

All beauty salons that offer manicures and pedicures have them. It is also easy to buy from chemist’s shops or pharmacies. Many households have acetones in their medicine or cosmetic cabinets. 

How To Choose A Solvent

Different types of substances have different properties as solutes and will only dissolve in solvents that have similar properties.

For example, a hydrophobic substance – one which repels or doesn’t mix with water – such as oil and fats will only dissolve in non-polar solvents. This is the reason why you should drink milk to relieve the burning sensation when eating spicy dishes. Milk has hydrophobic fatty components that can wash away the capsaicin oil from spices and chilli.

Choosing a solvent to use will largely depend on the following:

  • The substance you intend to dissolve
  • The type of chemical reaction you want to initiate
  • The quantity of solvent you need

Off-the-shelf solvents are commonly available from supermarkets, such as alkaline cleaning solvents and acids.

The quantity of solvent you need will depend on your intended application. Is it for industrial manufacturing purposes or you simply want to degrease your driveway?

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