Question

Write the net ionic equation for the reaction of \(\mathrm{FeCl}_{2}(\mathrm{aq})\) and \(\mathrm{AgNO}_{3}(\mathrm{aq})\). You may have to consult the solubility rules.

Short answer

\(\mathrm{Ag}^{+}(\mathrm{aq}) + \mathrm{Cl}^{-}(\mathrm{aq}) \rightarrow \mathrm{AgCl}(\mathrm{s})\)

Step-by-step solution

Write the balanced molecular equation

Identify the reactants and products. When \(\mathrm{FeCl}_{2}\) and \(\mathrm{AgNO}_{3}\) react, the products are \(\mathrm{Fe(NO}_{3})_{2}\) and \(\mathrm{AgCl}\). The balanced molecular equation is as follows: \[ \mathrm{FeCl}_{2}(\mathrm{aq}) + 2 \mathrm{AgNO}_{3}(\mathrm{aq}) \rightarrow \mathrm{Fe(NO}_{3})_{2}(\mathrm{aq}) + 2 \mathrm{AgCl}(\mathrm{s}) \]

Split aqueous compounds into ions

Write all aqueous compounds as dissociated ions. Solids remain intact (do not dissociate). \[ \mathrm{Fe}^{2+}(\mathrm{aq}) + 2 \mathrm{Cl}^{-}(\mathrm{aq}) + 2 \mathrm{Ag}^{+}(\mathrm{aq}) + 2 \mathrm{NO}_{3}^{-}(\mathrm{aq}) \rightarrow \mathrm{Fe}^{2+}(\mathrm{aq}) + 2 \mathrm{NO}_{3}^{-}(\mathrm{aq}) + 2 \mathrm{AgCl}(\mathrm{s}) \]

Identify and remove spectator ions

Spectator ions are ions that remain unchanged on both sides of the equation. In this case, \(\mathrm{Fe}^{2+}\) and \(\mathrm{NO}_{3}^{-}\) are spectators. Remove them to focus on the ions that change: The net ionic equation is: \[ 2 \mathrm{Ag}^{+}(\mathrm{aq}) + 2 \mathrm{Cl}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{AgCl}(\mathrm{s}) \]

Simplify the net ionic equation

The net ionic equation can be simplified by dividing all coefficients by 2, resulting in the simplest form: \[ \mathrm{Ag}^{+}(\mathrm{aq}) + \mathrm{Cl}^{-}(\mathrm{aq}) \rightarrow \mathrm{AgCl}(\mathrm{s}) \]

Key concepts

Solubility Rules

When dealing with chemical reactions in an aqueous solution, understanding solubility rules is crucial. Solubility rules help predict whether a compound will dissolve in water, forming aqueous ions, or remain undissolved as a solid. These rules can determine the state of compounds in reactions, thus influencing whether they participate in forming a precipitate.
The key solubility rules to remember include:

• Salts containing alkali metal ions (such as Li⁺, Na⁺) and ammonium ion ( NH₄⁺) are generally soluble.
• Nitrates ( NO₃⁻), acetates ( CH₃COO⁻), and perchlorates ( ClO₄⁻) are usually soluble.
• Most chloride ( Cl⁻), bromide ( Br⁻), and iodide ( I⁻) salts are soluble, except for those of silver, lead, and mercury.
• Sulfates ( SO₄²⁻) are generally soluble, with exceptions such as barium sulfate ( BaSO₄), lead sulfate ( PbSO₄), and strontium sulfate ( SrSO₄).

Applying solubility rules lets us conclude that when FeCl₂, reacts with AgNO₃, the AgCl produced is insoluble and thus forms a solid precipitate.

Molecular Equations

A molecular equation is the balanced chemical equation that represents the complete form of all the reactants and products in a chemical reaction. It shows the chemical formulas as compounds rather than their ionic forms present in solutions.
Molecular equations are straightforward to write and useful for recognizing the initial substances involved in the reaction.

• Begin by writing down all the compounds involved in the reaction at their start and end.
• Balance the equation by ensuring the number of atoms of each element is the same on both sides.

For instance, in the reaction between FeCl₂ and AgNO₃, the balanced molecular equation is FeCl₂(aq) + 2 AgNO₃(aq) → Fe(NO₃)₂(aq) + 2 AgCl(s). This process is simpler and emphasizes the relationship between reactants and products.

Spectator Ions

In a chemical reaction occurring in aqueous solutions, spectator ions are ions that appear in the same form on both the reactant and product sides of a chemical equation. These ions do not participate in the actual chemical change but remain dissolved in the solution.
To identify spectator ions, first, write down the complete ionic equation for the reaction.

• List all ions present in the reactants and products.
• Compare both sides and spot ions that remain unchanged in charge and composition.

In the example reaction, Fe^{2+} and NO₃^{-} appear unchanged on both sides and are thus spectator ions. Once identified, removing them from the ionic equation leaves the net ionic equation, which highlights only the ions actively participating in forming the solid precipitate, such as Ag⁺ and Cl⁻ in this case. Removing spectators simplifies understanding the reaction by focusing only on components that undergo actual change.