Water Chemical Properties

We all know how vital water is for the survival of living beings. Scientists have been probing Mars for decades together, just to find the slightest presence of water. Just last November, NASA stated that it found water on the moon, thereby paving a new path for development of lunar space station.

Why are scientists diligently carrying out all kinds of experiments to find water on other planets or satellites? Water is inevitable for the existence of life, simply because it makes a large part of an organism's body. In a way, it acts as a liquid skeleton, and prevents the body constituents from falling apart.

The chemical description of water is H₂O, which means that it is formed by the combination of two hydrogen atoms and one oxygen atom. The hydrogen atom weighs one-sixteenth of an oxygen atom. Thus, in water molecule, 88.8% of weight is from oxygen, while 11.2% belongs to hydrogen.

Though overall, water has a neutral charge, it tends to be slightly positive on the hydrogen side and slightly negative on oxygen side. The electrostatic bond formed between the slightly positive hydrogen ion of water molecule and other negative ions or polar molecules is termed as hydrogen bond.

Water has the capacity to dissolve more substances than any other liquid, and hence, is called a universal solvent. This enables this compound for transportation of valuable minerals, nutrients, or chemicals with them wherever they go. The polar bonds in water molecule make it a universal solvent.

Substances dissolving readily in water are called hydrophilic compounds. They consist of ions or polar molecules that attract water molecules due to their charge. The water molecules surround these ions and carry them into the solution, thereby resulting in their dissolution.

For example, ionic substances like sodium chloride dissolve in water, as the positive sodium ions and negative chlorine ions of sodium chloride get attracted to the polar water molecules.

Molecules with prevailing nonpolar bonds are the ones that are mostly insoluble in water, and are called hydrophobic compounds (for example, Hydrocarbons containing C-H bonds).

This is because the intensity by which water molecules are attracted to C-H bonds is far lesser than the intensity towards other water molecules. Hence, water does not carry these hydrocarbons into the solution.

The pH scale runs from 1 to 14, wherein a reading between 1-6 refers to acidic pH, while the one between 8-14 refers to basic pH. At pH 7, a compound is known to be neutral. The pH of a chemical substance is determined by the amount of hydrogen atoms in it.

Thus, a chemical compound with high pH has higher number of hydrogen atoms in its chemical composition and are called acids. Compounds with lower pH contains lower number of hydrogen atoms and are called bases. The pH of water is neutral.

Water has the ability to act as both an acid (proton donor) as well as a base (proton acceptor). It acts as a base to acids stronger than itself, and acts as an acid to bases stronger than itself. This amphoteric nature is clearly visible in the reaction given below, wherein water molecule reacts with acid as a base.

H₂O (l) + HCl (aq) ⇌ H₃O⁺⁺ Cl^-

Water molecule also reacts with a strong base as an acid.

H₂O (l) + NH₃ (aq) ⇌ NH₄⁺ + OH^-

Another interesting property is that metals such as gold, silver, copper, tin, etc. do not react with water. Moreover, although the chemical properties of salt water differ from that of regular water, due to the different dissolved salts present in them, the chemical properties of distilled water (DW) are the same as those of normal water. DW will only differ in its physical properties.