What are Weak Electrolytes, and Why are they called so?

The conduction of electricity lays a foundation in many phenomena we see in our daily lives. Without the conduction of electricity, we would be living in the stone age even today. The conduction of electricity is primarily observed in solids, but the transfer of electricity through liquids is an important field too.

The transfer of electricity through liquids is usually done with the help of electrolytes. Electrolytes are special substances that can be dissolved in a liquid to conduct electricity. They are either strong or weak electrolytes.

Electrolytes

A special substance that, when dissolved in liquid, typically water, and then undergoes a physical or chemical change to yield ions is called an electrolyte. Most of the compounds in nature are formed of two parts, one positive and one negative. A compound is called an ionic compound if it can produce a positive and negative component when it dissociates.

When an electrolyte is dissolved in a liquid, for example, water, the bonds in the electrolyte break to release a positively charged ion called the cation and a negatively charged ion called the anion. The presence of these ions is important as it permits electricity to be transferred through the liquid.

The transfer of electricity relies on the presence of charged species that are mobile. Therefore, when an electrolyte dissolves, it releases charged ions that are free to move. When electricity is passed through an electrolytic solution, the ions move from one side to another, which results in the conductance of electricity by the solution.

The identification of an electrolyte can be done through a simple example. In a beaker, take some amount of water. Add to it an electrolytic substance like table salt, NaCl. Now connect two bits of aluminium foil to the end of two wires connected to a plug. Add a bulb in series to one of the wires. Drop the aluminium foil in the beaker.

When the switch is turned on, the bulb will start glowing. This means that electricity is passing through the water. Now repeat the experiment, but this time replace water with ethanol and do not add any substance to it. Once the switch is turned on, the bulb does not glow.

Therefore, ethanol is not an electrolytic solution, but a saltwater solution is an electrolytic solution since it conducts electricity. The electrolyte in the solution is NaCl, which breaks to give Na+ and Cl- ions.

Classification of Electrolytes

Two important quantities are taken into consideration to classify an electrolyte into the category of strong and weak electrolytes.

Dissociation Constant

The dissociation constant is a special equilibrium constant that gives a measure of how easily an electrolyte can dissociate into its constituents. By using the Kohlrausch law, this constant value can be found out, which in turn can help in the understanding of the bonds in an electrolyte. 

A small constant value implies a stronger bond, while a large constant value implies vice versa. If an electrolyte has a larger value for its dissociation constant, then the electrolyte is assumed to dissociate very easily into its constituent ions when dissolved. However, an electrolyte with a small dissociation constant value will not readily produce ions when dissolved in a solvent.

Degree of Dissociation

An electrolyte must be subjected to an electric field to start dissociating. When an electric current is passed through an electrolytic solution, the current causes the molecules to split, resulting in the formation of ions. The degree of dissociation gives a measure of the degree to which a weak electrolyte will dissociate when an electric field of a certain strength is applied to it.

For strong electrolytes, the degree of dissociation changes slightly when the electric field is increased or decreased. However, the degree of dissociation changes drastically when the electric field strength is changed for weak electrolytes.

What are weak electrolytes and their properties?

Now that we know what the two bases of classifying electrolytes as strong or weak are, let us look at what these bases mean for weak electrolytes.

An electrolyte is termed a weak electrolyte if only a fraction of the electrolyte gets dissociated when the electrolyte is dissolved in a solution. This means that weak electrolytes do not produce a large number of ions when they are dissolved.

For a weak electrolyte, the dissociation constant value is less. The reason behind this is that weak electrolytes do not readily undergo the dissociation process, and therefore, they do not produce many ions in the solution. Since the dissociation constant gives an idea of the number of ions that an electrolyte will produce, its value is small for weak electrolytes.

Weak electrolytes do not produce many ions on their own. That is, they need some external energy to produce more ions. This means that if external energy like an electric field is applied to a weak electrolytic solution, then it will produce more ions, which can lead to better conductivity. When a weak electric field is applied, the degree of dissociation of the electrolytes is very less. 

However, when the strength of this electric field is increased, more ions are produced as the molecules receive more energy to break down. Therefore it can be said that with an increase in the strength of the external electric field, the degree of dissociation of a weak electrolyte increases.

Conclusion

The transfer of electricity through liquids is usually done with the help of electrolytes. Electrolytes are special substances that can be dissolved in a liquid to conduct electricity. They are either strong or weak electrolytes.

When an electrolyte is dissolved in a liquid, for example, water, the bonds in the electrolyte break to release a positively charged ion called the cation and a negatively charged ion called the anion. The presence of these ions is important as it permits electricity to be transferred through the liquid.

An electrolyte is termed a weak electrolyte if only a fraction of the electrolyte gets dissociated when the electrolyte is dissolved in a solution. This means that weak electrolytes do not produce a large number of ions when they are dissolved.