An aqueous solution allows an electric current to pass through it when it contains mobile ions. These ions are obtained from the dissociation of an electrolyte in water. The more mobile ions there are, the more conductive the solution.

In the following diagram, the aqueous solution of sodium chloride |(\text{NaCl}),| an electrolyte, contains mobile ions |\text{Na}^{+}| and |\text{Cl}^{-}.| This solution conducts an electric current, as evidenced by the light emitted by the light bulb.

An aqueous solution of NaCl contains mobile ions: Na+ and Cl-.

How Does Water Separate Electrolytes Into Ions?

Writing the Chemical Equation for Electrolytic Dissociation

Electrolytic dissociation is the separation of an electrolyte into a positive ion, called a cation, and a negative ion, called an anion in solutions.
An electrolyte is a substance that allows the passage of an electric current when it is in an aqueous solution.

The dissociation of an electrolyte can be represented by a chemical equation where:

The electrolyte is the reactant.
The cation and the anion are the products and are found in the aqueous phase (aq).
The cation and anion carry their respective charges.
The sum of charges of the cation and anion must be |0| (zero).

Water |(\text{H}_2\text{O})| is not usually represented in the chemical equation. It is the aqueous state (aq) of the products that indicates that they are dissolved in water.

Here is the chemical equation for the electrolytic dissociation of sodium chloride |(\text{NaCl}).|

||\begin{align}\text{NaCl}_{\text{(s)}}\ \rightarrow \ \text{Na}^{+}{_{\text{(aq)}}}\ +\ \text{Cl}^{-}{_{\text{(aq)}}}\end{align}||

|\text{NaCl}_{\text{(s)}}| is the electrolyte in solid state.
|\text{Na}{^+}{_{\text{(aq)}}}| is the cation in aqueous state with the charge |+1|.
|\text{Cl}{^-}{_{\text{(aq)}}}| is the anion in aqueous state with the charge |-1|.
The sum of charges is |+1+(-1)=0.|

The following procedure can be used to write the chemical equation for electrolytic dissociation.

Write the chemical formula of the electrolyte with its state as a subscript |\text{(s)}| on the reactant side, then an arrow to the right.
Separate the electrolyte into its cation and its anion and write them on the product side.
Using the periodic table, determine the respective charges of the cation and the anion and write them as superscripts.
Indicate the aqueous phase |\text{(aq)}| of the ions as a subscript.
If the chemical formula of the electrolyte includes subscripts, they become the coefficients of the ions.
Calculate the sum of charges to confirm that it is |0.|

Here is the chemical equation for the electrolytic dissociation of solid magnesium chloride |(\text{MgCl}{_2}{_{\text{(s)}}}).|

Write the chemical formula |\text{MgCl}{_2}| and the solid state subscript on the reactant side, then an arrow to the right.
|\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow|
Separate |\text{MgCl}{_2}| into the |\text{Mg}| cation and |\text{Cl}| anion and write the ions on the product side.
|\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow \ \text{Mg}\ +\ \text{Cl}|
Using the periodic table, determine that the |\text{Mg}| ion has a charge of |+2| and the |\text{Cl}| ion has a charge of |-1.| Write them as superscripts.
|\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow \ \text{Mg}^{2+}\ +\ \text{Cl}^{-}|
Indicate the aqueous phase of the ions.
|\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow \ \text{Mg}^{2+}{_{\text{(aq)}}}\ +\ \text{Cl}^{-}{_{\text{(aq)}}}|
The subscript |2| in |\text{Cl}_2| becomes the coefficient |2| in front of the |\text{Cl}^-| ion.
|\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow \ \text{Mg}^{2+}{_{\text{(aq)}}}\ +\ 2\ \text{Cl}^{-}{_{\text{(aq)}}}|
Calculate the sum of charges to confirm that it is |0.|
|\begin{alignat}{1}&\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow \ &\text{Mg}^{2+}{_{\text{(aq)}}}&\ +\ &2\ \text{Cl}^{-}{_{\text{(aq)}}}\\&&+2&\ +\ &2\times(-1)&\\&&+2&\ +\ &-2&=0\end{alignat}|

The chemical equation for the electrolytic dissociation of |\text{MgCl}{_2}{_{\text{(s)}}}| is |\text{Mg}\text{Cl}{_{2}}{_{\text{(s)}}}\ \rightarrow \ \text{Mg}^{2+}{_{\text{(aq)}}}\ +\ 2\ \text{Cl}^{-}{_{\text{(aq)}}}.|

Writing the Chemical Equation for Electrolytic Dissociation - Example 1

Determine the chemical equation for the electrolytic dissociation of solid calcium nitride |(\text{Ca}_{3}\text{N}{_{2}}{_{\text{(s)}}}).|

Writing the Chemical Equation for Electrolytic Dissociation - Example 2

See solution

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