Question

Write net ionic equations for the following reactions: (a) \(2 \mathrm{AuCl}_{3}(a q)+3 \mathrm{Sn}(s) \longrightarrow 3 \mathrm{SnCl}_{2}(a q)+2 \mathrm{Au}(s)\) (b) \(2 \operatorname{Nal}(a q)+\mathrm{Br}_{2}(l) \longrightarrow 2 \mathrm{NaBr}(a q)+\mathrm{I}_{2}(s)\) (c) \(2 \mathrm{AgNO}_{3}(a q)+\mathrm{Fe}(s) \longrightarrow$$\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Ag}(s)\)

Short answer

(a) \(2\mathrm{Au^{3+}} + 3\mathrm{Sn} \rightarrow 3\mathrm{Sn^{2+}} + 2\mathrm{Au}\); (b) \(2\mathrm{I^{-}} + \mathrm{Br}_{2} \rightarrow 2\mathrm{Br^{-}} + \mathrm{I}_{2}\); (c) \(2\mathrm{Ag^{+}} + \mathrm{Fe} \rightarrow \mathrm{Fe^{2+}} + 2\mathrm{Ag}\)."

Step-by-step solution

Write the Balanced Molecular Equation (a)

The given reaction is already balanced: \[2 \mathrm{AuCl}_{3}(aq) + 3 \mathrm{Sn}(s) \longrightarrow 3 \mathrm{SnCl}_{2}(aq) + 2 \mathrm{Au}(s)\] Identify the states of each compound: `aq` for aqueous and `s` for solid.

Write Complete Ionic Equation (a)

Separate all aqueous compounds into their constituent ions: \[2 \mathrm{Au^{3+}}(aq) + 6 \mathrm{Cl^{-}}(aq) + 3 \mathrm{Sn}(s) \longrightarrow 3 \mathrm{Sn^{2+}}(aq) + 6 \mathrm{Cl^{-}}(aq) + 2 \mathrm{Au}(s)\] Notice that solids do not split into ions.

Prepare Net Ionic Equation (a)

Cancel out spectator ions that appear on both sides of the equation: - The chloride ions \(\mathrm{Cl^{-}}\) are present on both sides.Resulting net ionic equation: \[2 \mathrm{Au^{3+}}(aq) + 3 \mathrm{Sn}(s) \longrightarrow 3 \mathrm{Sn^{2+}}(aq) + 2 \mathrm{Au}(s)\]

Write the Balanced Molecular Equation (b)

The given reaction is balanced as: \[2 \mathrm{NaI}(aq) + \mathrm{Br}_{2}(l) \longrightarrow 2 \mathrm{NaBr}(aq) + \mathrm{I}_{2}(s)\] Identify the states for each species: `aq` for aqueous, `l` for liquid, and `s` for solid.

Write Complete Ionic Equation (b)

Break down aqueous compounds into ions: \[2 \mathrm{Na^{+}}(aq) + 2 \mathrm{I^{-}}(aq) + \mathrm{Br}_{2}(l) \longrightarrow 2 \mathrm{Na^{+}}(aq) + 2 \mathrm{Br^{-}}(aq) + \mathrm{I}_{2}(s)\] Keep liquid and solid compounds as they are.

Prepare Net Ionic Equation (b)

Eliminate spectator ions (\(\mathrm{Na^{+}}\) appear on both sides):Resulting net ionic equation: \[2 \mathrm{I^{-}}(aq) + \mathrm{Br}_{2}(l) \longrightarrow 2 \mathrm{Br^{-}}(aq) + \mathrm{I}_{2}(s)\]

Write the Balanced Molecular Equation (c)

The given reaction balanced: \[2 \mathrm{AgNO}_{3}(aq) + \mathrm{Fe}(s) \longrightarrow \mathrm{Fe}(\mathrm{NO}_{3})_{2}(aq) + 2 \mathrm{Ag}(s)\] State identification is the same: `aq` for aqueous and `s` for solid.

Write Complete Ionic Equation (c)

Split the aqueous compounds into ions:\[2 \mathrm{Ag^{+}}(aq) + 2 \mathrm{NO3^{-}}(aq) + \mathrm{Fe}(s) \longrightarrow \mathrm{Fe^{2+}}(aq) + 2 \mathrm{NO3^{-}}(aq) + 2 \mathrm{Ag}(s)\] Fe remains as a solid and intact.

Prepare Net Ionic Equation (c)

Eliminate the \(\mathrm{NO3^{-}}\) ions that appear on both sides of the equation:Resulting net ionic equation: \[2 \mathrm{Ag^{+}}(aq) + \mathrm{Fe}(s) \longrightarrow \mathrm{Fe^{2+}}(aq) + 2 \mathrm{Ag}(s)\]

Key concepts

Ionic Compounds

Ionic compounds are substances formed by the chemical combination of positively charged ions (cations) and negatively charged ions (anions). These ions are held together by strong electrostatic forces known as ionic bonds. Ionic compounds typically form between metals and non-metals.

For example, in the reaction of gold(III) chloride with tin, the ionic compound \(\mathrm{AuCl_{3}}\) is made of gold cations \(\mathrm{Au^{3+}}\) and chloride anions \(\mathrm{Cl^{-}}\). When dissolved in water, these ionic compounds dissociate into their constituent ions, which is why you see them separated in ionic equations.

Ionic compounds have certain properties:

• They are usually solid at room temperature.
• They have high melting points due to strong ionic bonds.
• They conduct electricity when dissolved in water, as the ions are free to move.
• They form crystalline structures.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. These are represented using chemical equations, showing the reactants and products of the reaction.

A simple equation might look like:
\(2 \mathrm{NaI}(aq) + \mathrm{Br}_{2}(l) \longrightarrow 2 \mathrm{NaBr}(aq) + \mathrm{I}_{2}(s)\)

During a chemical reaction,

• Atoms rearrange to form new substances.
• Mass is conserved, as shown in balanced equations.
• The reaction can be exothermic (releasing energy) or endothermic (absorbing energy).
• Reactions can occur in different phases, such as solid, liquid, gas, or aqueous.

Chemical reactions are key in forming new products and releasing energy that can be harnessed in various applications.

Spectator Ions

Spectator ions are ions present in a solution that do not participate directly in a chemical reaction. They remain unchanged and can be found on both sides of a complete ionic equation.

For example, in the equation:
\(2 \mathrm{Ag^{+}}(aq) + 2 \mathrm{NO_{3}^{-}}(aq) + \mathrm{Fe}(s) \rightarrow \mathrm{Fe^{2+}}(aq) + 2 \mathrm{NO_{3}^{-}}(aq) + 2 \mathrm{Ag}(s)\)

The nitrate ions \(\mathrm{NO_{3}^{-}}\) are spectator ions.

They make no contribution to the formation of the product and can be eliminated to simplify the equation into the net ionic equation. Removing spectator ions helps focus on the chemistry occurring between the reacting ions.

• The presence of spectator ions does not affect the outcome of the reaction.
• They arise from dissolved ionic compounds.
• Simplifying reactions by omitting these ions aids in understanding reaction mechanics.

Balanced Equations

Balanced equations represent chemical reactions with the same number of each type of atom on both sides of the equation. This is a reflection of the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

For example, the balanced equation:
\(2 \mathrm{AgNO_{3}}(aq) + \mathrm{Fe}(s) \rightarrow \mathrm{Fe(\mathrm{NO_{3}})_{2}}(aq) + 2 \mathrm{Ag}(s)\)

Balances are necessary because they ensure:

• All atoms present in the reactants are accounted for in the products.
• Charge is balanced, especially important in ionic equations.
• Stoichiometry reflects the correct proportions needed for the reaction to occur.

Balancing equations often involves adjusting coefficients to ensure that all elements are equal on both sides, preserving the integrity of the actual reaction occurring.