Question

Write the balanced molecular, complete ionic, and net ionic equations for the reaction of ammonium sulfide with iron(III) chloride.

Short answer

Balanced molecular equation: \((NH_4)_2S + 6FeCl_3 \rightarrow 6NH_4Cl + 2Fe_2S_3\) Complete ionic equation: \(2NH_4^+ + S^{2-} + 6Fe^{3+} + 18Cl^- \rightarrow 12NH_4^+ + 18Cl^- + 2Fe_2S_3\downarrow\) Net ionic equation: \(S^{2-} + 6Fe^{3+} \rightarrow 2Fe_2S_3\downarrow\)

Step-by-step solution

Write the balanced molecular equation

First, we need to write the balanced molecular equation for the reaction of ammonium sulfide with iron(III) chloride. The reactants are ammonium sulfide \((NH_4)_2S\) and iron(III) chloride \(FeCl_3\). The products formed will be ammonium chloride \(NH_4Cl\) and iron(III) sulfide \(Fe_2S_3\). Now, we can write the balanced molecular equation: \((NH_4)_2S + 6FeCl_3 \rightarrow 6NH_4Cl + 2Fe_2S_3\)

Write the complete ionic equation

Next, we need to write the complete ionic equation by breaking down each soluble compound into its individual ions. The solubility rules state that all compounds containing ammonium ions and halides (except Ag, Hg, and Pb) are soluble. Therefore, we can separate ammonium sulfide and iron(III) chloride into their respective ions: \(2NH_4^+ + S^{2-} + 6Fe^{3+} + 18Cl^- \rightarrow 12NH_4^+ + 18Cl^- + 4Fe_2S_3\) However, we need to rewrite the equation without the iron(III) sulfide in ionic form because it is an insoluble compound: \(2NH_4^+ + S^{2-} + 6Fe^{3+} + 18Cl^- \rightarrow 12NH_4^+ + 18Cl^- + 4Fe_2S_3\downarrow\) Here, the down arrow indicates that the iron(III) sulfide formed is a precipitate (insoluble solid).

Write the net ionic equation

Finally, we will write the net ionic equation by removing spectator ions (ions that remain unchanged during the chemical reaction) from the complete ionic equation. In this case, the spectator ions are the ammonium ions \((NH_4^+)\) and the chloride ions \((Cl^-)\). After removing the spectator ions, our net ionic equation will be: \(S^{2-} + 6Fe^{3+} \rightarrow 2Fe_2S_3\downarrow\) This is the net ionic equation for the reaction of ammonium sulfide with iron(III) chloride.

Key concepts

Molecular Equation

A molecular equation represents the complete chemical formulas of the reactants and products in a chemical reaction. In the case of ammonium sulfide reacting with iron(III) chloride, each compound is written as a complete molecule.

For example, the balanced molecular equation for this reaction is:

• Ammonium sulfide: \((NH_4)_2S\)
• Iron(III) chloride: \(FeCl_3\)
• Ammonium chloride: \(NH_4Cl\)
• Iron(III) sulfide: \(Fe_2S_3\)

The balanced equation is written as:
\[(NH_4)_2S + 6FeCl_3 \rightarrow 6NH_4Cl + 2Fe_2S_3\]
This equation shows the overall transformation but does not provide details about the ions involved.

Ionic Equation

The ionic equation breaks down all the soluble ionic compounds into their respective ions. This helps us see what actually occurs at the ionic level during the reaction.

Using solubility rules, we identify which compounds dissociate in water.

• Ammonium sulfide dissociates into \(2NH_4^+\) and \(S^{2-}\)
• Iron(III) chloride dissociates into \(6Fe^{3+}\) and \(18Cl^-\)

The ionic equation includes these ions as they participate in the reaction, highlighting the changes in bonding and structure that occur in solution. However, insoluble compounds like \(Fe_2S_3\) remain intact in their original form.

Net Ionic Equation

The net ionic equation simplifies the reaction by removing spectator ions, which are ions that do not participate in the reaction. This equation shows only the ions and compounds directly involved.

In the reaction between ammonium sulfide and iron(III) chloride, the net ionic equation is:

• \(S^{2-} + 6Fe^{3+} \rightarrow 2Fe_2S_3\downarrow\)

By removing the spectator ions, like \(2NH_4^+\) and \(18Cl^-\), we focus only on the essentials. This helps to emphasize the formation of the precipitate \(Fe_2S_3\), which is the key change in the reaction.

Solubility Rules

Solubility rules are guidelines that help us predict whether a compound will dissolve in water. These rules are essential when working with ionic equations because they determine which compounds break into ions.

Key solubility rules include:

• Compounds with ammonium \((NH_4^+)\) or alkali metal ions are generally soluble.
• Halides are soluble except when paired with silver, mercury, or lead.
• Sulfides are generally insoluble except when combined with alkali metals or ammonium.

In our example, ammonium sulfide \((NH_4)_2S\) is soluble, while iron(III) sulfide \(Fe_2S_3\) forms an insoluble precipitate. These rules are essential for identifying which substances dissociate into ions and participate in chemical reactions.