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.

Short answer

(a) Balanced molecular equation: \(CdS (s) + H₂SO₄ (aq) \rightarrow CdSO₄ (aq) + H₂S (g)\) Net ionic equation: \(CdS (s) + 2 H⁺ (aq) \rightarrow Cd²⁺ (aq) + H₂S (g)\) Gas formed: Hydrogen sulfide (H₂S) (b) Balanced molecular equation: \(MgCO₃ (s) + 2 HClO₄ (aq) \rightarrow Mg(ClO₄)₂ (aq) + CO₂ (g)\) Net ionic equation: \(MgCO₃ (s) + 2 H⁺ (aq) \rightarrow Mg²⁺ (aq) + CO₂ (g)\) Gas formed: Carbon dioxide (CO₂)

Step-by-step solution

Write the unbalanced molecular equation

Cadmium sulfide (CdS) reacts with sulfuric acid (H₂SO₄) to form cadmium sulfate (CdSO₄) and hydrogen sulfide (H₂S) gas. Unbalanced molecular equation: CdS (s) + H₂SO₄ (aq) → CdSO₄ (aq) + H₂S (g)

Balance the equation

The equation is already balanced as written: CdS (s) + H₂SO₄ (aq) → CdSO₄ (aq) + H₂S (g)

Write the net ionic equation

First, split the aqueous compounds into their respective ions: CdS (s) + 2 H⁺ (aq) + SO₄²⁻ (aq) → Cd²⁺ (aq) + SO₄²⁻ (aq) + H₂S (g) Next, remove the spectator ion (SO₄²⁻), and write the net ionic equation: CdS (s) + 2 H⁺ (aq) → Cd²⁺ (aq) + H₂S (g) (b) Solid magnesium carbonate reacts with an aqueous solution of perchloric acid

Write the unbalanced molecular equation

Magnesium carbonate (MgCO₃) reacts with perchloric acid (HClO₄) to form magnesium perchlorate (Mg(ClO₄)₂) and carbon dioxide (CO₂) gas. Unbalanced molecular equation: MgCO₃ (s) + HClO₄ (aq) → Mg(ClO₄)₂ (aq) + CO₂ (g)

Balance the equation

To balance the equation, we need 2 moles of perchloric acid for every mole of magnesium carbonate: MgCO₃ (s) + 2 HClO₄ (aq) → Mg(ClO₄)₂ (aq) + CO₂ (g)

Write the net ionic equation

First, split the aqueous compounds into their respective ions: MgCO₃ (s) + 2 H⁺ (aq) + 2 ClO₄⁻ (aq) → Mg²⁺ (aq) + 2 ClO₄⁻ (aq) + CO₂ (g) Next, remove the spectator ion (ClO₄⁻), and write the net ionic equation: MgCO₃ (s) + 2 H⁺ (aq) → Mg²⁺ (aq) + CO₂ (g)