Features and significance of hydration in chemistry

The nature of the process and its main features

[Deposit Photos]

Hy­dra­tion in chem­istry has sig­nif­i­cance for many pro­cess­es. Hy­dra­tion in chem­istry is the at­tach­ment of wa­ter mol­e­cules to the mol­e­cule of an­oth­er sub­stance, if we’re talk­ing in gen­er­al terms. It is one of the main top­ics of study, as oth­er top­ics in chem­istry are based on this knowl­edge.

The main rea­son for this is that many re­ac­tions and pro­cess­es take place with wa­ter. In or­der to get a de­tailed un­der­stand­ing of hy­dra­tion, we should not only un­der­stand the na­ture of the process, but also its sig­nif­i­cance.

The na­ture of the process

In ex­am­in­ing the ques­tion “what is hy­dra­tion?”, we may sin­gle out a gen­er­al con­cept – it is the join­ing of par­ti­cles of a sub­stance dis­solved in wa­ter with wa­ter mol­e­cules. Sol­va­tion is also clas­si­fied as a type of hy­dra­tion.

The main dif­fer­ence of hy­dra­tion from hy­drol­y­sis is that this phe­nom­e­non does not lead to the de­struc­tion of the struc­ture of a wa­ter mol­e­cule, un­like hy­drol­y­sis.

As a re­sult of the process, hy­drates form – com­pounds which have a com­po­si­tion that is per­ma­nent or vari­able.


Crys­tal hy­drates are of­ten salts. They are char­ac­ter­ized by the fol­low­ing in­ter­ac­tions:

  • donor-ac­cep­tor;
  • dipole-dipole;
  • ion-dipole.

If a sol­id sub­stance is dis­solved in wa­ter, the crys­tal lat­tice dis­in­te­grates, and the mol­e­cules or ions sub­se­quent­ly go through the sol­va­tion process.

As a re­sult of hy­dra­tion, acids, al­ka­lis or am­pho­ter­ic com­pounds may form. Hy­dra­tion is pos­si­ble when the mol­e­cules of a sub­stance which have ex­cess en­er­gy are present in wa­ter. In this case they can at­tach to a wa­ter mol­e­cule with­out de­stroy­ing it.

The most in­ter­est­ing prop­er­ty of crys­tal hy­drates which form as a re­sult of hy­dra­tion is that de­pend­ing on the quan­ti­ty of at­tached wa­ter mol­e­cules, sub­stances with dif­fer­ent prop­er­ties may form. Prop­er­ties that may vary be­cause of this are:

  • wa­ter va­por pres­sure
  • form of crys­tal lat­tice
  • sol­u­bil­i­ty

If the same sub­stance is at­tached to a vary­ing quan­ti­ties of wa­ter mol­e­cules, com­pounds with dif­fer­ent char­ac­ter­is­tics may be ob­tained.

The re­versible process of hy­dra­tion is de­hy­dra­tion. It is usu­al­ly ap­plied to sol­id sub­stances and car­ried out by:

  • evap­o­ra­tion (usu­al­ly in a vac­u­um space);
  • heat­ing in an open space.


In cas­es with or­gan­ic sub­stances for re­mov­ing wa­ter mol­e­cules from a sub­stance, hy­dro­scop­ic agents may be used – for ex­am­ple sul­fu­ric acid.

The sig­nif­i­cance of hy­dra­tion

The hy­dra­tion process has enor­mous sig­nif­i­cance for chem­i­cal re­ac­tions. This is pri­mar­i­ly be­cause in many re­ac­tions wa­ter is present to on ex­tent or an­oth­er, as wa­ter is the main and most pop­u­lar sol­vent among all sub­stances. Click here to learn these pro­cess­es mak­ing amaz­ing chem­istry ex­per­i­ments.

Not ev­ery­one knows that the hy­dra­tion process is used in in­dus­try for the man­u­fac­ture of im­por­tant sub­stances:

  • acids;
  • al­co­hols;
  • alde­hy­des;
  • slaked lime.

Pro­cess­es of hy­dra­tion and de­hy­dra­tion con­stant­ly take place in the hu­man body. The me­tab­o­lism process takes place thanks to them. The cells of the or­gan­ism con­stant­ly ab­sorb and re­lease wa­ter. At the same time wa­ter ac­tive­ly bonds with oth­er sub­stances in the hu­man body.

Ex­am­ples of re­ac­tions

If we are ex­am­in­ing hy­dra­tion, it is im­por­tant to re­al­ize this is a process that can take place with the most var­ied sub­stances, and also lead to the for­ma­tion of sub­stances with dif­fer­ent prop­er­ties (salts form most of­ten).

As an ex­am­ple, we may ex­am­ine the fol­low­ing re­ac­tions.

The re­lease of var­i­ous crys­tals from a wa­ter so­lu­tion: Na₂­SO₄•10H₂O; Cu­SO₄•5H₂0; ВаС1•2Н₂0. These com­pounds are called crys­tal hy­drates, and the wa­ter in them is wa­ter of crys­tal­liza­tion. One of these com­pounds (Na₂­SO₄•10H₂O) may eas­i­ly give up wa­ter sim­ply on con­tact with air.

CuSO₄·5H₂O is bright blue and has a rather different structure from its colourless anhydrous derivative [Deposit Photos]

But Cu­SO₄•5H₂O may give up wa­ter if heat­ed.

At­tach­ment of wa­ter mol­e­cules:

СаО + Н₂O = Са(ОН)₂ or SO₃ + H₂O = H₂­SO₄

These re­ac­tions are ac­com­pa­nied by the grad­u­al re­lease of heat. Liq­uids are usu­al­ly formed. These com­pounds are called hy­drox­ides, and the wa­ter in them is wa­ter of con­sti­tu­tion;

At­tach­ment of wa­ter mol­e­cules to or­gan­ic com­pounds

When wa­ter bonds with eth­yl­ene in the pres­ence of bi­va­lent pal­la­di­um, acetic alde­hyde forms.

Hy­dra­tion of ions

By Taxman - http://bio.winona.edu/berg/ILLUST/Na+H2O.gif, Public Domain, Link

Hy­dra­tion of sodi­um-ion

In al­most all wa­ter so­lu­tions each ion is sur­round­ed by a shell of wa­ter. These com­pounds are known as ion hy­drates. If you run an elec­tric cur­rent through this so­lu­tion, the ions will not move sep­a­rate­ly, but rather the ion hy­drates will move to­geth­er. An im­por­tant prop­er­ty of these com­pounds is that the hy­dra­tion of ions de­creas­es as the con­cen­tra­tion of the so­lu­tion in­creas­es.

Swelling of col­loids

An ob­vi­ous ex­am­ple is gelatin. These chem­i­cal pro­cess­es have great im­por­tance for study­ing hu­man bi­ol­o­gy, as they ex­plain the process of mus­cle con­trac­tions, and how swelling forms. In some sources, one may also find the hy­dra­tion process cat­e­go­rized as a type of hy­drol­y­sis. But this is not quite cor­rect, as in the hy­drol­y­sis process the mol­e­cule of sub­stance breaks down, while in the hy­dra­tion process the struc­tural fea­tures of the wa­ter mol­e­cule do not change. This is­sue still re­mains un­der dis­cus­sion, as some sci­en­tists are in­clined to be­lieve this the­o­ry, while oth­ers see hy­dra­tion as a sep­a­rate in­de­pen­dent chem­i­cal process.

The study of hy­dra­tion con­tin­ues. Sci­en­tists of­ten use Monte Car­lo cal­cu­la­tions, and also molec­u­lar dy­nam­ics. These meth­ods are promis­ing for ex­pand­ing our knowl­edge about the hy­dra­tion of ions. Com­bin­ing re­search meth­ods is con­sid­ered to be most ef­fec­tive. Mod­ern the­o­ries are also based on meth­ods of com­pu­ta­tion­al ex­per­i­ments.

These stud­ies are im­por­tant for in­dus­tri­al dis­cov­er­ies, but also for a de­tailed study of me­tab­o­lism pro­cess­es in the hu­man body.