What does it do to stay hydrated

Under Hydration - often with Hydration or Hydration called - one understands

  • the accumulation of water molecules on dissolved ions. This creates a Hydrate shell (also as Hydrate sphere designated).
  • the accumulation of water molecules in solids (minerals) as crystal water
  • Hydration (but not hydration) is also called the reaction of water with alkenes (e.g. ethene), which creates an alcohol.

Accumulation of water molecules on ions in solution

The products formed during hydration are called hydrates. In other solvents, e.g. ammonia, similar effects occur, which are commonly referred to as solvation.

The hydration takes place due to the electrostatic forces between the charged ions and the water dipoles (ion-dipole interaction). With the formation of hydrogen bridges to the first hydrate shell, further water molecules can accumulate and thus form another hydrate sphere.

The hydration energy serves as a measure of the tendency of the ions to combine with water molecules. This is the energy that is required to bring the ions from the aqueous solution into the vacuum.

The number of bound water molecules and the strength of the bond depend on the size and charge of the ions. With the same charge, the smaller ions build up a larger hydrate shell than the larger ones. An "aq" on the ion indicates that the ion is hydrated:

In the case of small and / or multiply charged cations, the bound water molecules can give off protons, one speaks of Cation acids (see Lewis acids). In some cases, the solvent water cannot be removed from solutions containing cation acids:

Anions are generally much larger than cations and therefore less hydrated.

Addition of water to a C = C double bond (reaction)

This reaction is usually carried out in a strongly acidic aqueous solution. While the non-water component is broken down into two components during hydrolysis, it remains as one molecule during hydration.

The general formula of the reaction is:

RRC = CH2 in H2O (sour) → RRC-CH2-OH

In the first step, the acidic proton binds to the less substituted carbon atom of the double bond according to Markovnikov's rule. In the second step, an H.2O molecule to the more highly substituted carbon atom. At this point, the oxygen atom has three bonds and one positive charge. The proton is then taken over by another water molecule.

In laboratory practice, this reaction often leads to unwanted by-products and, in the simple form described here, is hardly suitable for the production of an alcohol. Oxymercuration is an alternative.

Here as an example the reaction of 1-methylcyclohexene to 1-methylcyclohexanol, with sulfuric acid as a catalyst.

Categories: Chemical Bond | Chemical reaction