Ionization of Electrolytes or Dissociation of Electrolytes

Before discussing the ionization or dissociation of electrolytes let us know what are electrolytes.

What are electrolytes?

There are some substances which can not exist in the molecular form in water. When we dissolve this type of substances in water, their molecules spontaneously break up into positive and negative ions. In other words, the molecules break up into two opposite charges. We call water dilute such substances as electrolytes.

Sodium Chloride as Electrolyte

To understand ionization or dissociation of electrolyte let us take an example of sodium chloride (NaCl) molecule. The atomic number of sodium (Na) is 11. Whereas the atomic number of chlorine (Cl) is 17. Let us draw the electronic arrangement in sodium (Na) atom and chlorine(Cl) atom.

sodium and chlorine atom

We know that each atom has various orbits. Each orbit consists of a specific number of electrons. The maximum number of electrons that can occupy an orbit we are 2n2. Where n is the serial number of the orbit. We count n from the orbit nearest to the nucleus. In other words, we number the orbit nearest to the nucleus as one. That means n = 1. Then, the next orbit is two (n = 2) and so on.

According to this principle, the maximum number of electrons in the first orbit is 2×12 = 2.

Then the maximum number of electrons in the second orbit is 2×22=8.

Similarly, the maximum number of electrons in the third orbit is 2×32 = 18.

Electronic Configuration of Sodium Atom

Since sodium (Na) has 11 electrons, the electronic configuration will be 2,8,1. Therefore the sodium(Na) only one electron in its outer orbit.

sodium atom

Electronic Configuration of Chlorine Atom

Then we come to the chlorine(Cl) atom. It has 17 electrons. So, the electronic configuration of the chlorine atom is 2,8,7.

chlorine atom

Ionic Bonds in Sodium Chloride

Hence, the outer most orbit of both sodium and chlorine do not have eight electrons. Due to this incompleteness of outer most orbit of both sodium and chlorine atoms, they become chemically active. So, when these two atoms come close to each other, sodium loses its outer most only electron. At the same time, the nearby chlorine atom accepts this electron to complete its outer most orbit with eight electrons. Consequently, the sodium becomes positively charged and the chlorine becomes negatively charged. Obviously, there is an electrostatic attraction force acting between them. And this force brings the sodium and the chlorine atoms together. In this way sodium chloride molecule forms.

attraction force of atom

 

Ionic Bond in Hydrochloric Acid

In a similar way the molecule of hydrochloric acid (HCl) forms. Likewise, we can explain the association of hydrogen with chlorine atoms. Here hydrogen loses its only electron then chlorine gains the same. Therefore positive hydrogen ion and negative chlorine ion form. Due to the electrostatic attraction between these two opposite ions, they associate each other.

Di-ionization of Sodium Chloride in Water

Let us dissolve sodium chloride in water. In water, the sodium chloride can not exist in its molecular form. In spite of it dissociate in Na+ and Cl ions.

Why does Sodium Chloride Dissociate in Water?

To answer this question we have to recall our knowledge about the expression of the electrostatic force between two electrical charges. According to Coulomb’s law, the expression of the electrostatic force is

In this expression suppose all quantities are constant except permittivity of the medium( ). That means we can change the electrostatic force between two charges by changing the surrounding medium. To put it another way, we can change the attraction force between Na+ and Cl by changing the medium. The permittivity of water is 80 times greater than that of air. Again the electrostatic force is inversely proportional to the permittivity. So, when we dissolve NaCl in water the electrostatic force acting between Na+ and Cl reduces to 80 times. Therefore the bonding  (ionic bond) between Na+ and Cl becomes quite weak. As a result, the molecule breaks up in the influence of normal thermal agitation. Finally, NaCl does not exist in its molecular form. We call this phenomenal as ionization or dissociation.

Dissociation of Dilute Hydrochloric Acid (HCl)

Similarly, ionization or dissociation of diluted HCl takes place. HCl exists into the water as H+ ions and Cl ions.

Dissociation of Dilute Copper Sulfate (CuSO4)

In a similar way copper sulfate (CuSO4) exists in its water solution as Cu++ ions and SO4– – ions.

Dissociation of Dilute Sulfuric Acid (H2SO4)

Likewise, H2SO4(sulfuric acid) exists as H+ ions and SO4– –  ions.

Example of Ionization of Dissociation

Ionization of acid always creates positive hydrogen ion and negative acid radical ion. The base always dissociates into positive metal and negative hydroxide ion (OH). In the case of salt, when we dissolve it in water it breaks up in metallic positive ions and non-metallic negative ions. For example, the ionization of sodium chloride gives Na+ and Cl ions. Similarly, copper sulfate gives Cu++ and SO42- ions. In the same fashion, AgNO3,  AgCl gives positive Ag+ and negative NO3, Cl ions respectively.

 

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