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Water (H 2 O) is an essential substance for the survival of living beings. It is made up of two hydrogen atoms and one oxygen atom. In nature it abounds in a liquid state but it can also be found in a solid state, in the form of ice and snow, or in a gaseous state, as water vapor.
The water is characterized by being colorless and odorless. 97% of the planet’s water is salty, such as the water of the seas and oceans. The rest is fresh water and is in aquifers, permafrost, lakes, rivers, soil moisture, atmospheric vapor, and living things. Much of the water is also in glaciers and ice caps.
Water also goes through a process known as the “hydrological cycle” through which it goes through different states: solid, liquid, and gas.
Water is of vital importance for natural ecosystems, climate regulation and human activities. Likewise, it forms 80% of most organisms, allowing the functioning of organs and tissues, as well as other vital processes.
Apart from these qualities, water is also considered as a natural and universal solvent. To better understand the reasons behind this statement it is necessary to understand the definition and characteristics of a solvent.
what is a solvent
A solvent is a substance in which a solute can be dissolved, resulting in the formation of a solution. Generally, the solvent is the most abundant component in a solution.
Solvents have different applications, both in the manufacture of adhesives, paints, and synthetic materials, as well as in pharmaceutical, cleaning and other products.
Taking into account the definition of a solvent, it can be said that a universal solvent is a substance that is capable of dissolving any other substance. However, there is no substance that can dissolve all the others; therefore, there is no real universal solvent. Instead, there are substances that can dissolve several similar substances. For example, if a solvent is polar, it may dissolve other polar solutes well, but it will not dissolve nonpolar solutes such as fats and oils. Conversely, if the solvent is nonpolar, it will be able to dissolve nonpolar solutes well, but not polar solutes.
Why is water considered a “universal solvent”?
Although there is no such thing as a universal solvent per se, water is called a universal solvent because, in addition to being the most common solvent there is, it dissolves more substances than any other known element. Being a polar solvent, water can dissolve organic and inorganic, ionic or neutral compounds.
The properties that make water an excellent solvent are the polarity of its molecules and its ability to form hydrogen bonds. The hydrogen side of each water molecule has a slight positive electrical charge, while the oxygen side carries a slight negative electrical charge.
This allows water to dissociate ionic compounds into positive and negative ions. The oxygen side attracts the positive part of the ionic compound and the positive hydrogen side attracts its negative part.
What makes a compound soluble in water?
The solubility of a molecule or ion depends on its ability to interact with water molecules. That is, it is determined according to the balance of forces between the molecules of the solvent and the solute. Temperature and pressure also influence the solubility of a substance.
Examples of substances that dissolve in water
Why does salt dissolve in water?
One of the most common examples of compounds that dissolve in water are salts. In particular, table salt, the one we use at home for cooking. In chemistry, this compound is called sodium chloride (NaCl).
As mentioned above, the solubility will depend on the polarity of the water and the solute. In this case, the sodium (Na) part has a positive charge, while the chlorine (Cl) part has a negative charge, and both ions are connected by an ionic bond.
On the other hand, hydrogen (H) and oxygen (O) that make up water are connected to each other by covalent bonds. Likewise, the hydrogen and oxygen atoms of the different water molecules are also linked by means of hydrogen bonds.
When salt is mixed with water, different attractive forces are produced between the ions of both compounds. Negatively charged oxygen anions are located near the sodium ion, while positively charged hydrogen ions are near the negatively charged chloride ion.
Although the ionic bonds are strong, the effect of the polarity of the water molecules is enough to separate the sodium and chlorine atoms. When salt separates, its ions disperse evenly, creating a homogeneous solution.
However, if too much salt is mixed in, it will not dissolve completely. Dissolution will occur until there are too many sodium and chlorine ions in the mixture. In that case, the force of the water molecules will not be enough to separate the ions. However, if the temperature is increased, this will increase the kinetic energy of the particles and more salt can be dissolved in the water.
Other substances that are soluble in water
Compounds that are soluble in water also include:
- Strong and weak acids and bases
- Some acidic and basic oxides
- Polar gases such as hydrogen chloride (HCL) or carbon dioxide (CO 2 ).
- alcohols
- Carboxylic acids
- Phenols, amines and amides
Examples of substances that do not dissolve in water
As mentioned above, water can easily dissolve polar substances. However, nonpolar substances, that is, substances that do not have any poles or do not have an unequal distribution of electrons, are not soluble in water.
In the case of nonpolar chemical compounds, they share electrons evenly and do not interact well with water molecules. Substances that are not soluble in water include:
- the oils
- The fats
- the waxes
- The oil
- The gas
- The ether
- acetone
- Some gases like methane (CH 4 )
- Insoluble vitamins, such as vitamins A, E, and D
Bibliography
- Chang, R. Chemistry . (2020). Spain. McGraw-Hill.
- Donelly, B. Organic Chemistry . (2020, audiobook). Audible. Northern Press.
- Oddone, S. Water: The Center of the Chemical Universe. (2021). Argentina. Editorial Authors of Argentina.
- Khan Academy. Solvent properties of water . Available at https://es.khanacademy.org/science/biology/water-acids-and-bases/hydrogen-bonding-in-water/a/water-as-a-solvent .
