Problem 41 - Chemistry: The Central Science

Question

Write balanced molecular and net ionic equations for the following reactions, and identify the gas formed in each: (a) solid cadmium sulfide reacts with an aqueous solution of sulfuric acid; (b) solid magnesium carbonate reacts with an aqueous solution of perchloric acid.

Step-by-Step Solution

Answer

The balanced net ionic equations for the given reactions are: (a) \(CdS_{(s)} + 2H^+_{(aq)} \rightarrow Cd^{2+}_{(aq)} + H_2S_{(g)}\) with hydrogen sulfide (H2S) gas formed. (b) \(MgCO_3_{(s)} + 2H^+_{(aq)} \rightarrow Mg^{2+}_{(aq)} + CO_2_{(g)}\) with carbon dioxide (CO2) gas formed.

Step 1: Write the unbalanced molecular equation

The given reaction can be represented as: \(CdS_{(s)} + H_2SO_4_{(aq)} \rightarrow\) products

Step 2: Identify the products

Cadmium sulfide reacts with sulfuric acid to form cadmium sulfate and hydrogen sulfide gas: \(CdS_{(s)} + H_2SO_4_{(aq)} \rightarrow CdSO_4_{(aq)} + H_2S_{(g)}\)

Step 3: Balance the molecular equation

The equation is already balanced: \(CdS_{(s)} + H_2SO_4_{(aq)} \rightarrow CdSO_4_{(aq)} + H_2S_{(g)}\)

Step 4: Write the complete ionic equation

As the reaction occurs in aqueous solution, dissociate the strong electrolytes: \(CdS_{(s)} + 2H^+_{(aq)} + SO_4^{2-}_{(aq)} \rightarrow Cd^{2+}_{(aq)} + SO_4^{2-}_{(aq)} + H_2S_{(g)}\)

Step 5: Write the net ionic equation

Remove spectator ions, which are the same on both sides of the equation: \(CdS_{(s)} + 2H^+_{(aq)} \rightarrow Cd^{2+}_{(aq)} + H_2S_{(g)}\) The balanced net ionic equation is: \(CdS_{(s)} + 2H^+_{(aq)} \rightarrow Cd^{2+}_{(aq)} + H_2S_{(g)}\) The gas formed is hydrogen sulfide (H2S). (b) Solid magnesium carbonate reacts with an aqueous solution of perchloric acid:

Step 1: Write the unbalanced molecular equation

The given reaction can be represented as: \(MgCO_3_{(s)} + HClO_4_{(aq)} \rightarrow\) products

Step 2: Identify the products

Magnesium carbonate reacts with perchloric acid to form magnesium perchlorate and carbon dioxide gas: \(MgCO_3_{(s)} + HClO_4_{(aq)} \rightarrow Mg(ClO_4)_2_{(aq)} + CO_2_{(g)}\)

Step 3: Balance the molecular equation

Balance the equation by adding coefficients: \(MgCO_3_{(s)} + 2HClO_4_{(aq)} \rightarrow Mg(ClO_4)_2_{(aq)} + CO_2_{(g)}\)

Step 4: Write the complete ionic equation

As the reaction occurs in aqueous solution, dissociate the strong electrolytes: \(MgCO_3_{(s)} + 2H^+_{(aq)} + 2ClO_4^-_{(aq)} \rightarrow Mg^{2+}_{(aq)} + 2ClO_4^-_{(aq)} + CO_2_{(g)}\)

Step 5: Write the net ionic equation

Remove spectator ions, which are the same on both sides of the equation: \(MgCO_3_{(s)} + 2H^+_{(aq)} \rightarrow Mg^{2+}_{(aq)} + CO_2_{(g)}\) The balanced net ionic equation is: \(MgCO_3_{(s)} + 2H^+_{(aq)} \rightarrow Mg^{2+}_{(aq)} + CO_2_{(g)}\) The gas formed is carbon dioxide (CO2).