Electrochemistry- Electrolytes and Non electrolytes

Electrolytes and Non-electrolytes:

Electrolytes: 

1)Electrolytes are chemical compounds that can break down into ions when dissolved in water.

2)Electrolytes can conduct electricity through their aqueous solutions.

3)Electrolytes are composed of ionic bonds.

4)Electrolytes are ionic compounds. Acids, base and salts are electrolytes.

5)Electrolytes can be found as strong electrolytes and weak electrolytes.

Non-electrolytes:

1)Nonelectrolytes are chemical compounds whose aqueous solutions cannot conduct electricity through the solution.

2)Nonelectrolytes cannot conduct electricity through their aqueous solutions.

3)Nonelectrolytes are composed of covalent bonds.

4)Nonelectrolytes are covalent compounds. Carbon-containing compounds, fat and sugar are nonelectrolytes.

5)Nonelectrolytes cannot be found as water-soluble compounds and water-insoluble compounds.

Lowry and Bronsted  concept of acids and  bases:

• According to Brønsted-Lowry theory acid is a proton (hydrogen ion) donor.
• According to Brønsted-Lowry theory base is a proton (hydrogen ion) acceptor.

For exmapl, consider the following chemical equation:

HCl(aq)+NH3(aq)---->NH+4(aq)+Cl−

Here, hydrochloric acid (HCl) "donates" a proton (H+) to ammonia (NH3) which "accepts" it , forming a positively charged ammonium ion (NH4+) and a negatively charged chloride ion (Cl-).

 Therefore, HCl is a Brønsted-Lowry acid (donates a proton) while the ammonia is a Brønsted-Lowry base (accepts a proton). Also, Cl- is called the conjugate base of the acid HCl and NH4+ is called the conjugate acid of the base NH3.

 Arrhenius theory of electrolytic dissociation (Ionic theory):

Postulates of the theory are : 

1) When an electrolyte is dissolved in water, its molecules spontaneously split into positively and negatively charged particles called ions. This process is called `dissociation or 'ionisation'. 

2) In a solution, the total positive charges on all the cations (+ve ions) and negative charges on all the anions (--ve ions) are exactly equal. Hence, the whole solution is electrically neutral. 

3) Ions are responsible for the passage of electric current through electrolytes.

4) Ionisation is a reversible process

5) The degree of ionisation of an electrolyte increases with dilution.

6) The properties of electrolytes are the properties of ions present in them.

 Evidences (merits) for Arrhenius theory:

 1) The theory satisfactorily explains the phenomenon of electrolysis and Faraday's laws of electrolysis.

2) Experimental observation shows that the conductance of a solution increases upon dilution. This is in agreement with the theory as more ions are formed during dilution.

3) The solutions of copper sulphate, cupric nitrate, cupric chloride are all blue because they all contain Cu2+ ions. This confirms that properties of electrolytes are properties of ions present in them.

4) Silver nitrate solution reacts with solutions of sodium chloride, potassium chloride, barium chloride etc. to develop a curdy white precipitate. This is possible because all these solutions contain chloride ions which combine with Ag+ ions of silver nitrate. 

        Ag+ + Cl-    - - - - - - - - >  Agcl

5) Ionic theory explains the constancy in enthalpy of neutralisation of any strong acid with any strong base.

6) Arrhenius theory explains the abnormality in the colligative properties (Eg.: osmotic pressure, elevation in boiling point etc.

Limitations (demerits) of Arrhenius theory:

1) The x-ray analysis of crystals like sodium chloride shows the existence of ions even in the solid state. Ions are also present in the molten state. However, according to the theory, ions are formed only in solution. 

2)The theory does not explain why ionisation takes place at all when an electrolyte is dissolved in water.

3)This theory not explain where the required energy for ionisation comes from.

4)The theory does not explain distinguish between the two types of electrolytes.

pH of a solution:

It is defined as 'negative logarithm to the base ten of molar concentration of hydrogen ions in the solution'. 

 pH = - log [H+]

pOH of a solution:

pOH of a solution is defined as 'negative logarithm to the base ten of molar concentration of hydroxyl ions in a solution'. 


pOH= - log[OH-]

pH scale: 

pH of a solution varies between 0 and 14. For neutral solution, pH is 7. For acidic solution, pH is between 0 and 7. For basic solution, pH is between 7 and 14.