Electrolytic dissociation - how to understand it?

You never thought about why somesolutions conduct electricity, and others - not? For example, everyone knows that it is better not to take a bath while putting hair with a hairdryer. After all, water is a good conductor of electric current, and if a working hair dryer falls into water, then a short circuit can not be avoided. In fact, water is not such a good conductor of current. There are solutions that conduct electricity much better. Such substances are called electrolytes. These include acids, alkalis and water-soluble salts.

Electrolytes - who are they?

The question arises: why solutions of some substances let electricity through, and others - not? It's all about charged particles - cations and anions. When dissolved in water, electrolytes break down into ions, which move under a given direction in the presence of an electric current. Positively charged cations move to the negative pole-the cathode, and the negatively charged anions move to the positive pole-the anode. The process of the decomposition of matter into ions during melting or dissolution in water has a proud name - electrolytic dissociation.

This term was put into circulation by the Swedish scientist S.Arrhenius, when he studied the properties of solutions to let electricity through. To do this, he closed the electrical circuit through a solution of any substance and watched the light comes on, or not. If the incandescent lamp lights up - the solution conducts electricity, which implies that this substance is an electrolyte. If the bulb remains extinct - then the solution does not conduct electricity, hence this substance - non-electrolyte. Non-electrolytes include solutions of sugar, alcohol, glucose. But the rastorov table salt, sulfuric acid and sodium hydroxide perfectly conduct electric current, hence they are electrolytic dissociation.

How is dissociation going on?

Subsequently, the theory of electrolytic dissociation was developed and supplemented by Russian scientists IA. Kablukov and V.A. Kistyakovskii, applying to its substantiation the chemical theory of solutions of D.I. Mendeleev University.

These scientists have found that electrolyticdissociation of acids, alkalis and salts occurs as a result of hydration of the electrolyte, that is, its interaction with water molecules. The ions, cations and anions formed as a result of this process will be hydrated, that is, connected with water molecules, which surround them with a dense ring. Their properties are significantly different from the non-hydrated ions.

Thus, in the solution of strontium nitrate Sr (NO3) 2, as well as in solutions of cesium hydroxide CsOH, electrolytic dissociation proceeds. Examples of this process can be expressed by the following reaction equations:

Sr (NO3) 2 = Sr2 + + 2NO3 -,

those. when one strontium nitrate molecule dissociates, one strontium cation and two nitrate anions are formed;

CsOH = Cs + OH-,

those. with the dissociation of one molecule of cesium hydroxide, one cesium cesium and one hydroxide anion are formed.

Electrolytic dissociation of acids occurs similarly. For hydroiodic acid, this process can be expressed by the following equation:

HJ = H + + CJ-,

those. when one molecule of hydroiodic acid dissociates, one hydrogen cation and one anion of iodine are formed.

Mechanism of dissociation.

The electrolytic dissociation of electrolyte substances proceeds in several stages. For substances with an ionic bond type, such as NaCl, NaOH, this process involves three successive processes:

Initially, water molecules having 2 unlike water moleculespoles (positive and negative) and representing a dipole, are oriented at the crystal ions. They attach a positive pole to the negative ion of the crystal, and vice versa, a negative pole to the positive ion of the crystal;
then the hydration of the crystal ions occurs with water dipoles,
and only after this as the hydrated ions to diverge in different directions and start to move in a solution or melt randomly as long as they will not work in the electric field.
For substances with a covalent polar bond, suchsuch as HCl and other acids, the process of dissociation is similar, except that at the initial stage, the covalent bond becomes ionic due to the action of water dipoles. These are the main points of the theory of dissociation of substances.