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) \(\mathrm{NH}_{3}+\mathrm{HNO}_{3} \longrightarrow\)

Short answer

(a) Net ionic: \( \mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) \). (b) Net ionic: \( 2\mathrm{H}^{+}(aq) + 2\mathrm{OH}^{-}(aq) \rightarrow 2\mathrm{H}_{2}\mathrm{O}(l) \). (c) Net ionic: \( 2\mathrm{H}^{+}(aq) + 2\mathrm{OH}^{-}(aq) \rightarrow 2\mathrm{H}_{2}\mathrm{O}(l) \). (d) Net ionic: \( \mathrm{NH}_{3}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{NH}_{4}^{+}(aq) \).

Step-by-step solution

Complete and Balance Equation (a)

The reaction involves sodium hydroxide (NaOH) reacting with nitric acid (HNO₃). In aqueous solutions, this is a typical neutralization reaction. The complete molecular equation is:\[ \mathrm{NaOH}(aq) + \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{NaNO}_{3}(aq) + \mathrm{H}_{2}\mathrm{O}(l) \]Since there is one atom of each element on each side of the equation, it is already balanced.

Net Ionic Equation (a)

In a net ionic equation, we only include the ions that participate in the reaction. The complete reaction equation is:\[ \mathrm{Na}^{+}(aq) + \mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) + \mathrm{NO}_{3}^{-}(aq) \rightarrow \mathrm{Na}^{+}(aq) + \mathrm{NO}_{3}^{-}(aq) + \mathrm{H}_{2}\mathrm{O}(l) \]Remove the spectator ions (which do not change during the reaction):\[ \mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) \]

Complete and Balance Equation (b)

The reactants, HCl and Ba(OH)₂, undergo a neutralization reaction:\[ \mathrm{2HCl}(aq) + \mathrm{Ba(OH)}_{2}(aq) \rightarrow \mathrm{BaCl}_{2}(aq) + \mathrm{2H}_{2}\mathrm{O}(l) \]This equation is balanced by ensuring two Cl atoms and four H atoms on each side.

Net Ionic Equation (b)

For the net ionic equation, focus on the ions involved:\[ \mathrm{2H}^{+}(aq) + 2\mathrm{Cl}^{-}(aq) + \mathrm{Ba}^{2+}(aq) + 2\mathrm{OH}^{-}(aq) \rightarrow \mathrm{Ba}^{2+}(aq) + 2\mathrm{Cl}^{-}(aq) + 2\mathrm{H}_{2}\mathrm{O}(l) \]Remove the spectator ions:\[ 2\mathrm{H}^{+}(aq) + 2\mathrm{OH}^{-}(aq) \rightarrow 2\mathrm{H}_{2}\mathrm{O}(l) \]

Complete and Balance Equation (c)

The reaction between acetic acid and calcium hydroxide:\[ 2\mathrm{HC}_{2}\mathrm{H}_{3}\mathrm{O}_{2}(aq) + \mathrm{Ca(OH)}_{2}(aq) \rightarrow \mathrm{Ca(C}_{2}\mathrm{H}_{3}\mathrm{O}_{2})_{2}(aq) + 2\mathrm{H}_{2}\mathrm{O}(l) \]Ensure all atoms are balanced, particularly 2 acetic acid molecules needed for 1 calcium hydroxide.

Net Ionic Equation (c)

Acetic acid is weak and partially ionizes, thus the net ionic equation focuses on participating ions from calcium hydroxide:\[ 2\mathrm{H}^{+}(aq) + 2\mathrm{OH}^{-}(aq) \rightarrow 2\mathrm{H}_{2}\mathrm{O}(l) \]

Complete and Balance Equation (d)

Ammonia reacting with nitric acid forms ammonium nitrate:\[ \mathrm{NH}_{3}(aq) + \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{NH}_{4}\mathrm{NO}_{3}(aq) \]This reaction is straightforward and balanced as written.

Net Ionic Equation (d)

The reaction simplified in ionic terms:\[ \mathrm{NH}_{3}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{NH}_{4}^{+}(aq) \]This equation highlights the transformation of ammonia to ammonium.

Key concepts

Molecular Equations

Molecular equations represent the overall chemical equation showing all the reactants and products as compounds with their respective phase labels. For example, when sodium hydroxide \((\text{NaOH})\) reacts with nitric acid \((\text{HNO}_3)\), it forms sodium nitrate \((\text{NaNO}_3)\) and water \((\text{H}_2\text{O})\), represented as: \[ \text{NaOH (aq) + HNO}_3\text{ (aq)} \rightarrow \text{NaNO}_3\text{ (aq) + H}_2\text{O (l)} \]. Each component of the reaction is shown in its original form, exactly as it appears in solution. Emphasis is placed on the full chemical species involved, rather than breaking them down into individual ions or simplified components. Key points to remember: - Molecular equations provide a complete representation of the chemical process. - They are often the initial step in approaching a reaction and lead to deeper analysis, such as balancing and net ionic equations.

Balancing Chemical Equations

Balancing chemical equations is crucial to reflect the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. This means the number of each type of atom must be the same on both sides of the equation. Here’s how you can balance equations effectively:

• Identify each reactant and product.
• List all the different atoms of each element present.
• Use coefficients to ensure the same number of each atom appears on both sides. For example, in the reaction between hydrochloric acid \((\text{HCl})\) and barium hydroxide \((\text{Ba(OH)}_2)\): \[ 2\text{HCl (aq) + Ba(OH)}_2\text{ (aq)} \rightarrow \text{BaCl}_2\text{ (aq) + 2H}_2\text{O (l)} \].
• The coefficients "2" in front of \(\text{HCl}\) and \(\text{H}_2\text{O}\) ensure a balanced equation.

Remember, coefficients adjust quantities but never change the actual formula of compounds or elements. Balancing not only interprets the stoichiometric relationship but also aids in predicting the amounts of substances consumed and produced in reactions.

Neutralization Reactions

Neutralization reactions are a type of chemical reaction where an acid and a base react to form water and a salt. This is a special case of double displacement reactions, typically occurring in aqueous solutions. Key characteristics include: - **Basic Reaction**: The general formula for neutralization is \(\text{Acid + Base} \rightarrow \text{Salt + Water}\). - **Example Reaction**: \(\text{NH}_3\) (a base) reacts with \(\text{HNO}_3\) (an acid) to form ammonium nitrate, \(\text{NH}_4\text{NO}_3\): \[ \text{NH}_3\text{ (aq) + HNO}_3\text{ (aq)} \rightarrow \text{NH}_4\text{NO}_3\text{ (aq)} \]. Here, the product, ammonium nitrate, is a salt resulting from this neutralization process. - **Ionic Perspective**: It often involves the transfer of protons, as demonstrated in ionic equations where the ions \(\text{H}^+\) and \(\text{OH}^-\) form \(\text{H}_2\text{O}\). These reactions are essential in various applications, from industrial processes to everyday products like antacids that neutralize stomach acidity. Understanding neutralization helps in many fields, especially chemistry and biology.