Problem 43 - General Chemistry

Question

Complete and balance each of the following molecular equations (in aqueous solution); include phase labels. Then, for each, write the net ionic equation. a. \(\mathrm{NaOH}+\mathrm{HNO}_{3} \longrightarrow\) b. \(\mathrm{HCl}+\mathrm{Ba}(\mathrm{OH})_{2} \longrightarrow\) c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}+\mathrm{Ca}(\mathrm{OH})_{2} \longrightarrow\) d. \(\mathrm{NH}_{3}+\mathrm{HNO}_{3} \longrightarrow\)

Step-by-Step Solution

Answer

Each molecular equation is balanced and has a net ionic equation, removing spectator ions.

Step 1a: Write the Complete Molecular Equation

For the reaction between NaOH and HNO₃, write the complete balanced molecular equation: \[ \text{NaOH} (aq) + \text{HNO}_3 (aq) \rightarrow \text{NaNO}_3 (aq) + \text{H}_2\text{O} (l) \] This reaction involves an acid-base neutralization reaction between sodium hydroxide and nitric acid.

Step 1b: Net Ionic Equation for Reaction a

Identify the ions in the complete molecular equation that are spectator ions (those that don't change). For NaOH and HNO₃, the net ionic equation is: \[ \text{OH}^- (aq) + \text{H}^+ (aq) \rightarrow \text{H}_2\text{O} (l) \] The sodium (Na⁺) and nitrate (NO₃⁻) ions are spectator ions and do not appear in the net ionic equation.

Step 2a: Write the Complete Molecular Equation

For the reaction between HCl and Ba(OH)₂, write the complete balanced molecular equation: \[ 2\text{HCl} (aq) + \text{Ba(OH)}_2 (aq) \rightarrow \text{BaCl}_2 (aq) + 2\text{H}_2\text{O} (l) \] This reaction involves hydrochloric acid and barium hydroxide.

Step 2b: Net Ionic Equation for Reaction b

Identify the ions in the complete molecular equation that are spectator ions. For HCl and Ba(OH)₂, the net ionic equation is: \[ 2\text{H}^+ (aq) + 2\text{OH}^- (aq) \rightarrow 2\text{H}_2\text{O} (l) \] The barium (Ba²⁺) and chloride (Cl⁻) ions are spectator ions and do not appear in the net ionic equation.

Step 3a: Write the Complete Molecular Equation

For the reaction between HC₂H₃O₂ and Ca(OH)₂, write the complete balanced molecular equation: \[ 2\text{HC}_2\text{H}_3\text{O}_2 (aq) + \text{Ca(OH)}_2 (aq) \rightarrow \text{Ca(C}_2\text{H}_3\text{O}_2)_2 (aq) + 2\text{H}_2\text{O} (l) \] This is a reaction between acetic acid and calcium hydroxide.

Step 3b: Net Ionic Equation for Reaction c

Identify the ions in the complete molecular equation that are spectator ions. For HC₂H₃O₂ and Ca(OH)₂, the net ionic equation is: \[ 2\text{CH}_3\text{COOH} (aq) + 2\text{OH}^- (aq) \rightarrow 2\text{CH}_3\text{COO}^- (aq) + 2\text{H}_2\text{O} (l) \] The calcium ion (Ca²⁺) is a spectator ion and does not appear in the net ionic equation.

Step 4a: Write the Complete Molecular Equation

For the reaction between NH₃ and HNO₃, write the complete balanced molecular equation: \[ \text{NH}_3 (aq) + \text{HNO}_3 (aq) \rightarrow \text{NH}_4\text{NO}_3 (aq) \] This reaction forms ammonium nitrate from ammonia and nitric acid.

Step 4b: Net Ionic Equation for Reaction d

Identify the ions in the complete molecular equation. For NH₃ and HNO₃, the net ionic equation is: \[ \text{NH}_3 (aq) + \text{H}^+ (aq) \rightarrow \text{NH}_4^+ (aq) \] In this reaction, no ions are spectator ions because ammonia reacts directly with hydrogen ions.

Key Concepts

Net Ionic Equations

In chemistry, a net ionic equation showcases only the particles that participate actively in a reaction. By focusing on the ions that undergo a chemical change, it helps us understand the essence of the reaction. For instance, in an acid-base reaction like that between NaOH and HNO₃:

• The complete equation is: \( \text{NaOH} (aq) + \text{HNO}_3 (aq) \rightarrow \text{NaNO}_3 (aq) + \text{H}_2\text{O} (l) \)
• The net ionic equation becomes: \( \text{OH}^- (aq) + \text{H}^+ (aq) \rightarrow \text{H}_2\text{O} (l) \)

Here, sodium (Na⁺) and nitrate (NO₃⁻) don't appear in the net ionic equation because they are spectator ions. The net ionic equation highlights only those ions that form the final product, water in this case.

Spectator Ions

Spectator ions are the ions present in a reaction mixture that do not undergo any chemical change. They remain in the solution throughout the reaction, simply "watching" the action without participating. In the reaction of hydrochloric acid with barium hydroxide:

• The complete molecular equation reads: \( 2\text{HCl} (aq) + \text{Ba(OH)}_2 (aq) \rightarrow \text{BaCl}_2 (aq) + 2\text{H}_2\text{O} (l) \)
• Here, barium (Ba²⁺) and chloride (Cl⁻) ions are spectator ions. They are present in the same form both before and after the reaction.

By identifying spectator ions, you can simplify the equation, focusing on the true chemical change.

Molecular Equations

Molecular equations represent the compounds involved in a chemical reaction as complete formulas. These equations give a clear picture of the substances’ state—whether they are in aqueous or solid form, for example. Consider the balanced molecular equation for the reaction of HC₂H₃O₂ (acetic acid) with Ca(OH)₂ (calcium hydroxide):

• The balanced equation is: \( 2\text{HC}_2\text{H}_3\text{O}_2 (aq) + \text{Ca(OH)}_2 (aq) \rightarrow \text{Ca(C}_2\text{H}_3\text{O}_2)_2 (aq) + 2\text{H}_2\text{O} (l) \)
• Molecular equations do not break down compounds into ions, instead offering an overview of the reactants and the products in their neutral forms.

This approach simplifies the study of reactions, especially when understanding what each molecule contributes to the overall chemical process.